Parallel Declines in Pollinators and Insect-Pollinated Plants in Britain and the Netherlands

Abstract

Despite widespread concern about declines in pollination services, little is known about the patterns of change in most pollinator
assemblages. By studying bee and hoverfly assemblages in Britain and the Netherlands, we found evidence of declines (pre-versus
post-1980) in local bee diversity in both countries; however, divergent trends were observed in hoverflies. Depending on the
assemblage and location, pollinator declines were most frequent in habitat and flower specialists, in univoltine species,
and/or in nonmigrants. In conjunction with this evidence, outcrossing plant species that are reliant on the declining pollinators
have themselves declined relative to other plant species. Taken together, these findings strongly suggest a causal connection
between local extinctions of functionally linked plant and pollinator species.

Full text

domain substituted by the hydrophobic tail of
H-Ras was not (Fig. 4D). Ra c1 is of parti c ul ar
importance to Fc receptor-mediated phagocytosis
and accumulates at the base of forming phago-
somes, detaching rapidly upon sealing (Fig. 4, E
and F, and fig. S7A) (10). Rac1(Q61L) also de-
tached from sealing phagosomes with kinetics
indistinguishable from those of wild-type Rac1
(Fig. 4, G and H, and movie S7). Because
Rac1(Q61L) is constitutively bound to guanosine
triphosphate (GTP), its dissociation from phago-
somes was not due to nucleotide hydrolysis or
cessation of nucleotide exchange. Instead, release
waslikelymediatedbytermination of its electro-
static association with the plasmalemma. Accord-
ingly, the C-terminal tail of Rac1 containing the
polybasic domain behaved similarly (fig. S7B).
Our data indicate that the surface potential of
the inner leaflet of the membrane decreases locally
during phagosome formation. The change is at-
tributable primarily to depletion of PIP
2
and PS,
but depletion of phosphatidylinositol 4-phosphate
was also observed (fig. S3 and movie S5). Activa-
tion of inositide lipases, kinases, and phosphatases
occurs during phagocytosis and bacterial invasion
(3), readily accounting for the changes in PIP
2
.PS
could be converted to PE by decarboxylation or
could be externalized during phagocytosis by
scramblases and/or efflux pumps.
Our results also indicate that the anchor-
age of important signaling molecules, includ-
ing K-Ras and Rac1, can be modulated focally
by localized changes in surface potential. Other
proteins anchored electrostatically to the mem-
brane, such as MARCKS, are equally suscepti-
ble to the charge alterations that accompany
lipid remodeling. Indeed, we also obtained
evidence for localized detachment of the
tyrosine kinase c-Src (fig. S5, B and C).
The consequences of altered surface charge in
other important biological phenomena must be
considered. Activation of phosphoinositide metab-
olism, elevation in cytosolic calcium, and PS
flipping occur after stimulation of multiple
receptors and channels as well as during apoptosis.
The effect of such responses on inner surface
potential may be measurable with the use of
approaches like the one described here. Cycles of
membrane dissociation/reassociation may add a
layer of functional control to complement the
traditional biochemical mode of regulation of sig-
naling proteins.
References and Notes
1. M. Olivotto, A. Arcangeli, M. Carla, E. Wanke, Bioessays
18, 495 (1996).
2. S. McLaughlin, A. Aderem, Trends Biochem. Sci. 20, 272
(1995).
3. R. J. Botelho, C. C. Scott, S. Grinstein, Curr. Top.
Microbiol. Immunol. 282, 1 (2004).
4. R. Leventis, J. R. Silvius, Biochemistry 37, 7640 (1998).
5. See supporting material on Science Online.
6. M. O. Roy, R. Leventis, J. R. Silvius, Biochemistry 39,
8298 (2000).
7. J. B. McCabe, L. G. Berthiaume, Mol. Biol. Cell 12, 3601
(2001).
8. J. F. Hancock, H. Paterson, C. J. Marshall, Cell 63, 133
(1990).
9. D. Michaelson et al., J. Cell Biol. 152, 111 (2001).
10. A. D. Hoppe, J. A. Swanson, Mol. Biol. Cell 15, 3509
(2004).
11. We thank E. Pick for providing Rac1 and D. Russell for
providing Nucleosil beads. Supported by the Canadian
Institutes for Health Research and an NIH grant, by a
Canadian Institutes of Health Research studentship (T.Y.),
and by the Pitblado Chair in Cell Biology (S.G.).
Supporting Online Material
www.sciencemag.org/cgi/content/full/313/5785/347/DC1
Materials and Methods
Figs. S1 to S7
Movies S1 to S7
4 May 2006; accepted 5 June 2006
10.1126/science.1129551
Parallel Declines in Pollinators and
Insect-Pollinated Plants in
Britain and the Netherlands
J. C. Biesmeijer,
1
*
S. P. M. Roberts,
2
M. Reemer,
3
R. Ohlemu¨ ller,
4
M. Edwards,
5
T. Peeters,
3,6
A. P. Schaffers,
7
S. G. Potts,
2
R. Kleukers,
3
C. D. Thomas,
4
J. Settele,
8
W. E. Kunin
1
Despite widespread concern about declines in pollination services, little is known about the
patterns of change in most pollinator assemblages. By studying bee and hoverfly assemblages in
Britain and the Netherlands, we found evidence of declines (pre- versus post-1980) in local bee
diversity in both countries; however, divergent trends were observed in hoverflies. Depending on
the assemblage and location, pollinator declines were most frequent in habitat and flower
specialists, in univoltine species, and/or in nonmigrants. In conjunction with this evidence,
outcrossing plant species that are reliant on the declining pollinators have themselves declined
relative to other plant species. Taken together, these findings strongly suggest a causal connection
between local extinctions of functionally linked plant and pollinator species.
A
nthropogenic changes in habitats and
climates have resulted in substantial re-
ductions in biodiversity among many
vertebrate taxa (1), and evidence has been ac-
cumulating that insect biodiversity is at risk as
well (2). Of particular concern is the possibility
of community-level cascades of decline and
extinction (3), whereby decline of some ele-
ments of the biota lead to the subsequent loss of
other species that directly or indirectly rely upon
them. Here we examine sets of pollinators and
the plants that they pollinate to test (i) whether
species that are linked to one another within
communities show coincident declines and (ii)
whether species with more links within com-
munities are more robust to change because of
the availability of alternative links, if an inter-
acting species is lost.
Any loss in biodiversity is a matter of public
concern, but losses of pollinating insects may
be particularly troubling because of the poten-
tial effects on plant reproduction. Many agricul-
tural crops and natural plant populations are
dependent on pollination and often on the ser-
vices provided by wild, unmanaged, pollinator
communities. Substantial concerns have been
raised about the decline or loss of these services
E(4) but see (5)^, culminating in formal rec-
ognition within the Convention on Biological
Diversity (6)intheS,o Paulo Declaration (7)
and the International Initiative for the Conser-
vation and Sustainable Use of Pollinators (8).
However, the evidence for such declines re-
mains scanty (5).
To adequately demonstrate a decline in pol-
linator services, one would need to document
(i) overall declines in pollinator density; and/or
(ii) reductions in species diversity or substantial
shifts in the species composition of pollinator
communities, combined with changes in the
distribution of traits represented in those com-
munities (thus indicating that the loss of some
pollinators has not been compensated by the
rise of functionally equivalent species); and (iii)
declines in either the reproductive success or
abundance of plant species dependent on these
pollinators. No suitable data are available to
address overall pollinator density, but here we
provide evidence for the remaining points,
using data for bees, hoverflies, and plants from
Britain and the Netherlands.
We compiled almost 1 million records for
bee (all native species except the largely
1
Institute of Integrative and Comparative Biology and Earth
and Biosphere Institute, University of Leeds, Leeds, LS2 9JT,
UK.
2
Centre for Agri-Environmental Research, University of
Reading, Reading, RG6 6AR, UK.
3
European Invertebrate
Survey–Netherlands/National Museum of Natural History
Naturalis, Postbus 9517, 2300 RA Leiden, Netherlands.
4
Department of Biology, University of York, York, YO10 5YW,
UK.
5
Lea-side, Carron Lane, Midhurst, GU29 9LB, West
Sussex, UK.
6
Department of Animal Ecology, Bargerveen
Foundation, Radboud University of Nijmegen, Postbox 9010,
6500 GL Nijmegen, Netherlands.
7
Nature Conservation and
Plant Ecology Group, Wageningen University and Research
Centre, Bornesteeg 69, 6708 PD Wageningen, Netherlands.
8
Umweltforschungszentrum–Centre for Environmental Re-
search Leipzig-Halle, Community Ecology (Biozo
¨
nosefor-
schung), Theodor-Lieser-Strasse 4, 06120 Halle, Germany.
*To whom correspondence should be addressed. E-mail:
j.c.biesmeijer@leeds.ac.uk
www.sciencemag.org SCIENCE VOL 313 21 JULY 2006
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REPORTS

domesticated honeybee Apis mellifera)and
hoverfly observations for both countries from
national entomological databases (9), focusing
on areas with extensive sets of observations
before and after 1980. We then applied
rarefaction methods to compare species rich-
ness of focal areas over each period (10). This
approach allows valid comparisons between
time periods, despite unequal sample sizes and
the incorporation of records collected by many
recorders who used different collecting tech-
niques over long time spans (10).
Bee diversity declined in large fractions
of the 10 km by 10 km cells analyzed in both
countries (Fig. 1). Bee richness was measured
as the number of distinct species; significant de-
creases in richness were observed in 52% and
È67% of British and Dutch cells, respectively, as
compared with richness increases in 10% and 4%
of cells in the two countries (table S1). Shifts in
hoverfly diversity were less consistent (Fig. 1),
with no significant directional change in richness
for the UK (increases in 25% and decreases in
33% of British cells); however, increases in
hoverfly richness were reported in 34%, versus
decreases in 17%, of Dutch cells (table S1).
These shifts in species richness reflect
shifts in the distributions of many species in
both groups. Our data set does not allow di-
rect measurement of population densities of
the species involved; nonetheless, shifts over
time in the relative number of records for dif-
ferent species can be used as an indicator of
their relative frequency and ubiquity (10).
There has been an increase in the domination of
the pollinator communities of both countries by
a smaller number of species. For both taxa in
both countries, about 30% fewer species ac-
count for half of the post-1980 records (percent-
ages of fewer species: British bees, 29%;
British hoverflies, 29%; Netherlands bees,
32%; Netherlands hoverflies, 36%). In Britain,
the species that increased were dispropor-
tionately the ones that were already common
before 1980; however, in the Netherlands, this
wasnotthecase(11).
The functional diversity of pollination net-
works contributes to the maintenance of diver-
sity in plant communities (12), with different
groups of pollinators being complementary in
their pollination services and different groups
of plants being complementary in their roles as
food plants for pollinators. Consequently, a de-
cline in pollinator diversity might have little
effect on a community if the fluctuating species
were functionally similar. However, the traits
of increasing and declining species of solitary
bees and hoverflies differ in consistent ways
(Table 1). In both countries and in both groups,
species with narrow habitat requirements have
experienced greater relative declines. In solitary
bees, oligolectic species (those using few flower
taxa as food sources) have declined significant-
ly in Britain, and long-tongued taxa have
declined significantly in the Netherlands. Die-
tary specialization is important in hoverflies as
well, with both adult and larval diets being
strongly related to changes in hoverfly occur-
rence. Migratory hoverflies have fared better
than nonmigratory species in both countries. In
Britain, bee and hoverfly declines are greater
among species with only a single generation per
year; however, this pattern is not found in the
Netherlands. The significant trends indicate that
specialized species Ei.e., in habitat and dietary
requirements and, arguably, tongue length
(12, 13)^ and species characterized by slower
development and lower mobility (those having
fewer generations per year and being non-
migratory) tend to decline more than general-
ist, fast developing, and more mobile species.
Such shifts in pollinator traits suggest pos-
sible shifts in pollination services. Indeed,
recent experiments have shown that the func-
tional diversity of pollinators can affect diver-
sity in plant communities (12). We know of no
data that will allow us to assess directly
whether rates of pollinator visitation or pollen
depositiontoflowershave shifted appreciably
in Britain or the Netherlands. We can, however,
examine shifts in plant species distributions
using floral inventories from both countries
(10, 14, 15) to see whether shifts in plants are
consistent with the observed shifts in pollina-
tors. In Britain, obligately outcrossing plants
reliant on insect pollinators were declining on
average; species reliant on abiotic (wind or
water mediated) pollination were increasing;
and self-pollinating plant species showed an in-
termediate response (Table 2). In the Nether-
lands, changes were not significantly different
among these three groups; however, given the
observed decline in bees and increase in hov-
erflies in the Netherlands, divergent trends
between bee-pollinated plants and other insect-
pollinated plants may be expected there. After
reexamining the data on the insect taxa reported
as pollinators of outcrossing plants (15), we
found that, on average in the Netherlands, plants
that were exclusively pollinated by bees were
declining, but plants pollinated by flies and other
insects (including bees) were increasing. If the
changes among bee-pollinated outcrossers, out-
Fig. 1. Bee and hoverfly richness has changed in many of the 10 km by 10 km cells analyzed for
Britain and the Netherlands. Some British cells contained adequate data only on eusocial or only
on solitary bees (10). Changes in species richness were calculated from rarefaction analyses (10).
21 JULY 2006 VOL 313 SCIENCE www.sciencemag.org
352
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crossers with abiotic pollination, and predomi-
nantly self-pollinating plants are compared, the
trends observed in the Netherlands mirror those
for Britain: Bee-dependent plants have declined,
abiotically pollinated plants have increased, and
plants mainly relying on self-pollination have
shown an intermediate response (Table 2).
We cannot tell from these data whether the
decline of the plants precedes the loss of the
associated pollinators, whether the decline of
the pollinators leads to the loss of reproductive
function and then to the decline of the plants, or
indeed whether the plants and their pollinators
are both responding to some other factor. How-
ever, the results clearly show that linked ele-
ments in biological communities (i.e., specialist
pollinators and the obligately outcrossed plants
that they pollinate) are declining in tandem.
Furthermore, the difference between the two
countries implies that there is probably a causal
link, because it is the corresponding groups of
plants and pollinators in both countries that are
changing. The hypothesis that species that rely
on a broader range of other species within a
community are more robust in the face of change
is supported by the following evidence: Polli-
nators that rely on few plants for their resources
have declined the most, whereas generalists
have prospered Ecompare with (16)^. Moreover,
the decline of bees (specialized as pollinators)
relative to hoverflies (having broader feeding
habits) could be interpreted in this light.
Demonstrating that there are shifts in pol-
linator assemblages and associated changes in
wild plant communities in two countries does
not prove the existence of a global pollination
crisis. Britain and the Netherlands are not only
two of the countries with the best available data
but also two of the most densely populated and
anthropogenically modified landscapes on the
planet. Few British habitats can be thought of
as truly natural, and in the Netherlands the
landscape is largely artificial. Nonetheless, it
seems probable that shifts similar to those
documented for these countries will be found
in other parts of northwest Europe and, in-
creasingly, in other regions (17). Documenting
the geographical extent of the declines shown
here is a priority for future research. It is also
important to begin mechanistic studies of the
causes of these declines, with habitat alteration
(18), climate change (19–21), and agricultural
chemical usage (18, 22) being potential key drivers
of observed shifts (23).
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database of EIS-NL, the Dutch Youth Organisation for
Nature Study, and the Dutch Entomological Society.
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J.C.B. from data of the UK Bees, Wasps, and Ants
Recording Society. British hoverfly data were obtained
from the National Biodiversity Network
(www.searchnbn.net), largely based on the Hoverfly
Recording Scheme.
10. Materials and methods are available as supporting
material on Science Online.
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totals for significantly declining versus significantly
increasing species: British bees, P 0 0.005; British
Table 1. Trait-based patterns in pollinator declines. Proportions are based on species that showed
significant change in the number of cells (n) in which they were reported during the two time
periods (pre- and post-1980). Declining solitary bee and hoverfly species tend to be found more
among the specialists (characterized by narrow habitat ranges, limited dietary choice, slower
development, and greater residency) than among generalist species (characterized by wide habitat
ranges, broader dietary choice, multiple generations per year, and greater tendency toward
migration). Traits were assigned by using methodologies in (25)and(26). Bumblebees and
honeybees were excluded from the analysis (10). Oligo, oligolectic; Poly , polylectic; Uni, univoltine;
Multi, multivoltine; Macro, macroorganisms; Micr o, microorganisms; Res, resident; Mig, migran t.
Britain Netherlands
Solitary bees
Trait Trait category Pn Trait category Pn
(proportion declining) (proportion declining)
Habitat range Narrow Wide Narrow Wide
(0.90) (0.25) 0.0001 32 (0.83) (0.53) 0.090 29
Flower specificity Oligo Poly Oligo Poly
(0.86) (0.41) 0.034 34 (0.55) (0.76) 0.198 36
Tongue length Long Short Long Short
(0.70) (0.41) 0.099 56 (1.00) (0.51) 0.028 49
Generations Uni Multi Uni Multi
(0.60) (0.14) 0.042 44 (0.76) (0.55) 0.433 42
Hoverflies
Trait Trait category Pn Trait category Pn
(proportion declining) (proportion declining)
Habitat range Narrow Wide Narrow Wide
(0.96) (0.28) 0.0001 53 (0.52) (0.25) 0.025 67
Adult food Narrow Wide Narrow Wide
(0.63) (0.41) 0.095 60 (0.53) (0.16) 0.0001 86
Larval food Macro Micro Macro Micro
(0.74) (0.43) 0.009 59 (0.59) (0.20) 0.002 79
Generations Uni Multi Uni Multi
(0.80) (0.29) 0.0001 50 (0.43) (0.38) 0.63 88
Migration Res Mig Res Mig
(0.63) (0.20) 0.01 64 (0.46) (0.17) 0.025 88
Table 2. Mean relative change (TSE) in distribution of British (27) and Netherlands (28)plant
species according to their main pollen vector (10). Insect-pollinated outcrossing plants in Britain and
bee-pollinated outcrossing plants in the Netherlands have declined, whereas plants with abiotic
pollination have increased. Plant breeding systems were derived by combining the ECOFL OR (29)and
BIOLFL OR (30) databases (10). British data were tested with an analysis of variance and a post hoc
Tukey test. Netherlands data were tested with a Kruskal-Wallis test and a post hoc multiple comparison
test. Superscripts indicate group differences based on post hoc tests. n, number of plant species; NL,
Netherlands.
Obligatory outcrossing,
insect pollinated
Obligatory outcrossing,
wind or water pollinated
Predominantly
self pollinating
P
Britain –0.22 T 0.06* þ0.18 T 0.14
†
–0.003 T 0.70*
†
0.009
(n 0 75) (n 0 30) (n 0 116)
Netherlands þ0.10 T 0.08 þ0.18 T 0.08 –0.08 T 0.11 0.091
(n 0 182) (n 0 160) (n 0 143)
NL bee plants –0.12 T 0.13* þ0.18 T 0.08
†
–0.08 T 0.11*
†
0.036
(n 0 42) (n 0 160) (n 0 143)
www.sciencemag.org SCIENCE VOL 313 21 JULY 2006
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REPORTS

hoverflies, P G 0.0001; Netherlands bees, P 0 0.07 (the
reverse trend); Netherlands hoverflies, P 0 0.10.
12. C. Fontaine, I. Dajoz, J. Meriguet, M. Loreau, PLoS Biol. 4,
e1 (2006).
13. M. Stang, P. G. L. Klinkhamer, E. Van der Meijden, Oikos
112, 111 (2006).
14. C. D. Preston, D. A. Pearman, T. D. Dines, New Atlas of
the British and Irish Flora: An Atlas of the Vascular Plants
of Britain, Ireland, the Isle of Man, and the Channel
Islands (Oxford Univ. Press, Oxford, 2002).
15. Biobase 2003, Centraal Bureau voor de Statistiek,
Voorburg/Heerlen, The Netherlands (2003).
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London Ser. B 271, 2605 (2004).
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Europe (Pedagogical University, Bydgoszcz, Poland,
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23. A Europe-wide assessment of the risks associated with
pollinator loss and its drivers is currently being under-
taken within the 6th European Union Framework
Programme–Assessing Large-scale Environmental Risks
for Biodiversity with Tested Methods project [GOCE-CT-
2003-506675 (www.alarmproject.net)], of which this
study is a core element (24).
24. J. Settele et al., GAIA 14, 69 (2005).
25. S.P.M.R. compiled trait data of European bees from
published sources (see www.alarmproject.net).
26. M. Speight, E. Castella, J.-P. Sarthou, C. Monteil, Eds.,
Syrph the Net on CD, Issue 2. The Database of European
Syrphidae (Syrph the Net Publications, Dublin, 2004).
27. Change indices from (14) were calculated from occu-
pancy data in surveys conducted from 1930 to 1969 and
from 1987 to 1999.
28. Comparison of the number of 5 km by 5 km cells
occupied in 1940 and 1990. Data from Biobase (15)
were organized into frequency classes by A.P.S. (10).
29. The Ecological Flora of the British Isles at the University
of York (www.york.ac.uk/res/ecoflora/cfm/ecofl/index.cfm).
30. S. Klotz, I. Ku
¨
hn, W. Durka, Eds. BIOLFLOR: A Database
on Biological and Ecological Traits of the German Flora
(Bundesamt fu
¨
r Naturschutz, Bonn, 2002).
Supporting Online Material
www.sciencemag.org/cgi/content/full/313/5785/351/DC1
Materials and Methods
Figs. S1 and S2
Tables S1 and S2
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24 March 2006; accepted 6 June 2006
10.1126/science.1127863
Crystal Structure of a Divalent
Metal Ion Transporter CorA at
2.9 Angstrom Resolution
Said Eshaghi,
1
*
† Damian Niegowski,
1,2
*
Andreas Kohl,
1
Daniel Martinez Molina,
1,2
Scott A. Lesley,
3
Pa
¨
r Nordlund
1
†
CorA family members are ubiquitously distributed transporters of divalent metal cations and are
considered to be the primary Mg
2þ
transporter of Bacteria and Archaea. We have determined a
2.9 angstrom resolution structure of CorA from Thermotoga maritima that reveals a pentameric cone–
shaped protein. Two potential regulatory metal binding sites are found in the N-terminal domain that
bind both Mg
2þ
and Co
2þ
. The structure of CorA supports an efflux system involving dehydration and
rehydration of divalent metal ions potentially mediated by a ring of conserved aspartate residues at
the cytoplasmic entrance and a carbonyl funnel at the periplasmic side of the pore.
D
ivalent metal cations are essential co-
factors in many proteins. To provide
cells with appropriate concentrations
of divalent metal cations, highly regulated
transporters and channels have evolved to
translocate these ions across the hydrophobic
membranes. CorA is one of the best studied
families of divalent cation transporters (1–9).
It is considered to be the primary Mg
2þ
trans-
porter of both Bacteria and Archaea and is
ubiquitously distributed (8). Sequence homolo-
gies between members of this family are most
pronounced at the C termini; sequence conser-
vation in the N termini is less significant (fig.
S1). The overall sequence similarity between
eukaryotes and prokaryotes is weak, except for
the highly conserved Gly-Met-Asn (GMN)
motif close to the C termini (10, 11). Never-
theless, some eukaryotic CorA family members
show overlapping activities with the prokary-
otic members that suggests functional, as well
as structural, conservation (4, 10, 12, 13).
Studies of CorA from Salmonella typhimurium,
Escherichia coli, and the Archaeon Methano-
coccus jannaschii demonstrate that ions can be
transported in both directions (1–3, 5, 8, 9).
Kehres and Maguire recently reported two
classes of CorAs among Bacteria and Archaea
(8). The second class, CorA-II, which differs
from the extensively studied S. typhimurium
and E. coli CorAs, was suggested to contain
two transmembrane helices, with both termini
in the cytosol. In the same report, the CorA-II
proteins were suggested to be efflux systems.
Moreover, a novel CorA-related protein, ZntB,
was recently identified in S. typhimurium (14).
ZntB was shown to be a Zn
2þ
efflux system
with two predicted transmembrane helices and
both termini facing the cytosol (15). This is in
contrast with the predicted topology of S.
typhimurium and E. coli CorA, with three trans-
membrane helices and the N terminus facing
the periplasm.
Here, we report the crystal structure of a
full-length CorA homolog from Thermotoga
maritima,at2.9) resolution. The recently
reported structure of a pentameric full-length
CorA at 3.9 ) was used for molecular
replacement, revealing two pentamers in
the asymmetric unit (16). The structure has
been refined to an R of 27.6% and an R
free
of
29.5% with good stereochemistry (table S1).
The CorA structure reveals a pentamer with
the shape of a cone (Fig. 1). The tip of the cone
is formed by two transmembrane (TM) helical
segments from each monomer and the large
opening of the cone by the N-terminal region
of CorA. The fold of the CorA monomer is
composed of an N-terminal a/b domainwitha
central seven-stranded mixed b sheet lined by
three small helices. Two long a helices cover
one face of the a/b domain and form a bundle
together with a giant a helix 7 constituted by
È70 residues. The C-terminal end of helix 7
constitutes the first transmembrane segments
(residues 291 to 312). Following the large helix
7 is helix 8 (residues 327 to 349), which forms
the second TM helix and packs in a ring around
the TM segment of helix 7 (Fig. 1).
Thermotoga maritima CorA is most closely
related to the class II CorA with both N- and
C-terminal ends facing the cytosol and, there-
fore, is likely to be primarily involved in ion
efflux. The localization of the N termini in the
cytoplasm is also supported by the positive-
inside rule (17)andtheN
in
-C
in
topology of
Bhelical hairpin[ structures (18). Sequence
alignment of close homologs of T. maritima
CorA and those of S. typhimurium CorA sup-
port the proposal for two distinct classes of
CorA (fig. S1).
Our structure agrees in all general features
with the structure determined by Lunin et al.
(16) that was used for phasing. However, be-
cause of the higher resolution of 2.9 ), our
structure provides more details of functionally
important regions, including potential regulato-
ry metal binding sites beyond the metal in site 1
(M1) identified in the 3.9 ) structure. Two
putative metal-binding sites are found at each
interface between the N-terminal domains in
the pentamer (Fig. 2). An anomalous difference
map of Co
2þ
-soaked crystals shows that Co
2þ
1
Division of Biophysics, Department of Medical Bio-
chemistry and Biophysics, Karolinska Institute, SE-171 77
Stockholm, Sweden.
2
Department of Biochemistry and
Biophysics, Stockholm University, S-106 91 Stockholm,
Sweden.
3
Joint Center for Structural Genomics and
Genomics Institute of the Novartis Research Foundation,
San Diego, CA 92121, USA.
*These authors contributed equally to this work.
†To whom correspondence should be addressed. E-mail:
Par.Nordlund@ki.se (P.N.); Said.Eshaghi@ki.se (S.E.)
21 JULY 2006 VOL 313 SCIENCE www.sciencemag.org
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