Pyroglutamate Amyloid-? (A?):
A Hatchet Man in Alzheimer
Published, JBC Papers in Press,September 29, 2011, DOI 10.1074/jbc.R111.288308
Sadim Jawhar, Oliver Wirths, and Thomas A. Bayer1
Göttingen,UniversityMedicineGöttingen,37075 Göttingen, Germany
Pyroglutamate-modified amyloid-? (A?pE3) peptides are
gaining considerable attention as potential key participants in
in AD brain, high aggregation propensity, stability, and cellular
toxicity. Transgenic mice that produce high levels of A?pE3–42
have proven that the enzyme glutaminyl cyclase catalyzes the
formation of A?pE3. In this minireview, we summarize the cur-
rent knowledge on A?pE3, discussing its discovery, biochemical
properties, molecular events determining formation, preva-
lence in the brains of AD patients, Alzheimer mouse models,
and potential as a target for therapy and as a diagnostic marker.
When Alois Alzheimer presented the case of his patient
Auguste Deter at the Tübingen meeting of the Southwest Ger-
man Psychiatrists in 1906, he did not attract much attention or
stimulate any discussion in the audience. The young doctor
likely would not have believed that, 100 years later, the disease
that now holds his name would be the most common cause of
dementia and a source of a critical medical and economical
problem. At this meeting, Alzheimer presented Auguste
Deter’s symptoms and reported the histopathological features
that are now associated with Alzheimer disease (AD)2: neuron
loss, extracellular amyloid plaques, and intracellular neurofi-
brillary tangles. For more than 2 decades, the amyloid hypoth-
of AD etiology. The amyloid hypothesis considers amyloid-?
(A?) deposition to be the causative event of AD pathology and
that neurofibrillary tangles, cell loss, vascular damage, and
recently suggested that the extracellular formation of A?
plaques and other AD pathological events are preceded by
intraneuronal A? accumulation, giving rise to a modified amy-
loid hypothesis (2).
The story of successful discoveries in modern AD research
using novel molecular biological tools started with the bio-
chemical analysis of ?-amyloid-containing blood vessels (con-
gophilic amyloid angiopathy) (3) and amyloid plaques consis-
ting of A? (4), which led to the isolation and sequencing of the
gene encoding the larger amyloid precursor protein (APP) (5,
In vitro and in vivo analyses of amyloid deposits in AD
revealed various N- and C-terminal variants (4, 7, 8). Increased
C-terminal length of A? (from A?x–40to A?x–42) in AD
enhanced aggregation and early deposition and promoted the
novel toxic peptide in AD (12).
acid (A?1–x), several N-terminally truncated and modified A?
species have been described (4, 13–15). Among A? species
a relatively abundant species in AD, aged control, and vascular
with mass spectrometry, Portelius et al. (17) showed that
A?1–40, A?1–42, A?pE3–42, and A?4–42are the dominant frac-
tions in AD hippocampus and cortex. Interestingly, it has been
demonstrated that N-terminal deletions enhance A? aggrega-
tion by comparing A?x–42with A?1–42(9).
In addition, biochemical studies showed that A? peptides
isolated from AD brains were post-translationally modified by
isomerization and racemization (18, 19). A? isomerized at the
seventh amino acid was suggested to compose a major fraction
of A? in neuritic plaques (20). Both modifications have been
shown to accelerate peptide aggregation and fibril formation
(18, 21, 22). Other modifications include metal-induced oxida-
tion (23) or phosphorylation (24, 25). In general, N-terminal
modifications significantly influence the Cu2?coordination of
sity, redox activity, and resistance to degradation (26). In addi-
tion, it has been shown that certain apolipoprotein E isoforms
ing isomerized and pyroglutamate-modified A? (A?pE3) (27).
The controversy among different studies regarding the pre-
might reflect differences in the brain regions analyzed, imbal-
ances in age and disease stages of the recruited cases, different
Discovery of Pyroglutamate A?
to develop approaches to extract and study the biochemical
nature of A?. Limited extraction and sequencing methods ren-
dered it impossible for a long time. Attempts to extract and
study the composition of A? plaques from brains of AD
patients started in the 1970s (28, 29). However, discrepancies
existed between different reports describing the amino acid
cedures. The first successful protocol to purify and study the
sequence of amino acids of A? was developed by Glenner and
* This work was supported by the Competence Network Degenerative
minireview will be reprinted in the 2011 Minireview Compendium, which
will be available in January, 2012.
1To whom correspondence should be addressed. E-mail: email@example.com.
2The abbreviations used are: AD, Alzheimer disease; A?, amyloid-?; APP,
amyloid precursor protein; A?pE3, pyroglutamate-modified A?; DS, Down
syndrome; QC, glutaminyl cyclase; PS1, presenilin-1; KO, knock-out; hQC,
human QC; PIB, Pittsburgh compound-B.
THE JOURNAL OF BIOLOGICAL CHEMISTRY VOL. 286, NO. 45, pp. 38825–38832, November 11, 2011
© 2011 by The American Society for Biochemistry and Molecular Biology, Inc.Printed in the U.S.A.
This paper is available online at www.jbc.org
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in A?, showing similarity between AD and DS patients. In a
et al. (4) reported the presence of ragged N termini of A?
extracted from the plaque cores of AD and DS patients.
According to them, 64% of the total A? peptides started with
phenylalanine at position 4. Soon after that, Selkoe et al. (31)
reported that they were not able to obtain N-terminal
sequences from plaques using purification with SDS-contain-
ing buffer without protease treatment. Thus, they suggested
that the N terminus of A? might be blocked (31). In line with
this, other teams did not succeed in obtaining interpretable
N-terminal sequences from plaque cores isolated by other
used in previous reports (33).
deposition of pyroglutamate A? has increased. Many tech-
niques and protocols were developed to increase the sensitivity
to different forms of A?, especially the A?pEpeptides (34, 35).
present in equivalent or larger amounts than full-length A? in
senile plaques. On the basis of analysis of brain tissue from DS
cases, the authors also suggested that A?pE3–xprecedes the
deposition of unmodified A? (A?1–x). However, a study on the
sequential deposition of heterogeneous forms of A? in the
brains of DS patients could not detect A?pE3in young patients.
Nevertheless, in agreement with the results of Saido et al.,
A?pE3always exceeded the deposition of A?1(36). This was
further confirmed by another study on water-soluble A? dem-
dominant fraction (37). In line with the previous findings, test-
ing extracts from AD and DS frontal cortex using ELISA
revealed that levels of A?pE3and isomerized A? species ending
(38, 39). This was further confirmed by the finding that
A?pE3–42constituted 25% of the total A?x–42in plaques of AD
can be modified into A?pE3after being injected into rat brain,
indicating that rat brains harbor the enzymes required for
N-terminal truncation and pyroglutamate formation (40).
N-terminal Truncation Is a Prerequisite of Pyroglutamate
Formation of pyroglutamate-modified A? is a multistep
process requiring the removal of the first two amino acids,
aspartate and alanine, to expose the N-terminal glutamate at
the third position of A? (Fig. 1). After cleavage of APP by the
major ?-site APP-cleaving enzyme (BACE1) and ?-secretase,
A?1–40/42is liberated. Data from our group suggest that the
levels of A?pE3–xare inversely linked to the levels of A?1–xin
plaques in APP/PS1KI transgenic mice (41). In line with this
can trigger the initial first amino acid (aspartate) cleavage of
A?. Interestingly, more than 15 years ago, Saido et al. (15) sug-
glutamate at position 3 of the N terminus of A?. Subsequently, glutamate is post-translationally modified to N-terminal pyroglutamate (pE) by dehydration
the higher aggregation propensity and the longer bioavailability of the A?pE3oligomers.
38826 JOURNALOFBIOLOGICALCHEMISTRY VOLUME286•NUMBER45•NOVEMBER11,2011
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J. Biol. Chem.
Sadim Jawhar, Oliver Wirths and Thomas A.
Man in Alzheimer Disease
): A Hatchet
doi: 10.1074/jbc.R111.288308 originally published online September 29, 2011
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