Structure and regulation of Kit protein-tyrosine kinase--the stem cell factor receptor.

Abstract

Signaling by stem cell factor and Kit, its receptor, play important roles in gametogenesis, hematopoiesis, mast cell development and function, and melanogenesis. Moreover, human and mouse embryonic stem cells express Kit transcripts. Stem cell factor exists as both a soluble and a membrane-bound glycoprotein while Kit is a glycoprotein receptor protein-tyrosine kinase. The complete absence of stem cell factor or Kit is lethal. Gain-of-function mutations of Kit are associated with several human neoplasms including acute myelogenous leukemia, gastrointestinal stromal tumors, mastocytomas, and nasal T-cell lymphomas. Binding of stem cell factor to Kit results in receptor dimerization and activation of protein kinase activity. The activated receptor becomes autophosphorylated at tyrosine residues that serve as docking sites for signal transduction molecules containing SH2 domains. Kit activates Akt, Src family kinases, phosphatidylinositol 3-kinase, phospholipase Cgamma, and Ras/mitogen-activated protein kinases. Kit exists in active and inactive conformations as determined by X-ray crystallography. Kit consists of an extracellular domain, a transmembrane segment, a juxtamembrane domain, and a protein kinase domain that contains an insert of about 80 amino acid residues. The juxtamembrane domain inhibits enzyme activity in cis by maintaining the control alphaC-helix and the activation loop in their inactive conformations. The juxtamembrane domain also inhibits receptor dimerization. STI-571, a clinically effective targeted protein-tyrosine kinase inhibitor, binds to an inactive conformation of Kit. The majority of human gastrointestinal stromal tumors have Kit gain-of-function mutations in the juxtamembrane domain, and most people with these tumors respond to STI-571. STI-571 binds to Kit and Bcr-Abl (the oncoprotein of chronic myelogenous leukemia) at their ATP-binding sites.

Full text

Page 1

Breakthroughs and Views
Structure and regulation of Kit protein-tyrosine kinase—The stem
cell factor receptorq
Robert Roskoski Jr.*
Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, 1100 Florida Avenue, New Orleans, LA 70119, USA
Received 17 September 2005
Available online 4 October 2005
Abstract
Signaling by stem cell factor and Kit, its receptor, play important roles in gametogenesis, hematopoiesis, mast cell development and
function, and melanogenesis. Moreover, human and mouse embryonic stem cells express Kit transcripts. Stem cell factor exists as both a
soluble and a membrane-bound glycoprotein while Kit is a glycoprotein receptor protein-tyrosine kinase. The complete absence of stem
cell factor or Kit is lethal. Gain-of-function mutations of Kit are associated with several human neoplasms including acute myelogenous
leukemia, gastrointestinal stromal tumors, mastocytomas, and nasal T-cell lymphomas. Binding of stem cell factor to Kit results in recep-
tor dimerization and activation of protein kinase activity. The activated receptor becomes autophosphorylated at tyrosine residues that
serve as docking sites for signal transduction molecules containing SH2 domains. Kit activates Akt, Src family kinases, phosphatidyl-
inositol 3-kinase, phospholipase Cc, and Ras/mitogen-activated protein kinases. Kit exists in active and inactive conformations as deter-
mined by X-ray crystallography. Kit consists of an extracellular domain, a transmembrane segment, a juxtamembrane domain, and a
protein kinase domain that contains an insert of about 80 amino acid residues. The juxtamembrane domain inhibits enzyme activity
in cis by maintaining the control aC-helix and the activation loop in their inactive conformations. The juxtamembrane domain also
inhibits receptor dimerization. STI-571, a clinically effective targeted protein-tyrosine kinase inhibitor, binds to an inactive conformation
of Kit. The majority of human gastrointestinal stromal tumors have Kit gain-of-function mutations in the juxtamembrane domain, and
most people with these tumors respond to STI-571. STI-571 binds to Kit and Bcr-Abl (the oncoprotein of chronic myelogenous leuke-
mia) at their ATP-binding sites.
? 2005 Elsevier Inc. All rights reserved.
Keywords: Abl; Activation loop; Acute myelogenous leukemia; Bcr-Abl; Cell signaling; Chronic myelogenous leukemia; Flt3; Dysgerminoma; Germ cells;
Gleevec; Mast cells; Nasal T-cell lymphoma; Oncogene; Proto-oncogene; Seminoma; STI-571, Targeted cancer therapy
Protein kinases are enzymes that play a key regulatory
role in nearly every aspect of cell biology [1]. They regu-
late apoptosis, cell cycle progression and proliferation,
cytoskeletal rearrangement, differentiation, development,
the immune response, motility, nervous system function,
and transcription. Owing to the myriad actions of protein
kinases, it is imperative that they be stringently regulated
because aberrant activity of these enzymes leads to a vari-
ety of diseases including cancer, diabetes, and autoim-
mune,cardiovascular,inflammatory,
disorders. Considerable effort has been expended to deter-
mine the physiological and pathological functions of pro-
teinkinasesignal transduction
mutations and dysregulation of protein kinases play caus-
al roles in human disease, these enzymes represent attrac-
tive drug targets [2].
Protein kinases catalyze the following reaction:
and nervous
pathways. Because
MgATP1?þ protein-OH ! protein-OPO2?
3þ MgADP þ Hþ
Based upon the nature of the phosphorylated –OH group,
these enzymes are classified as protein-serine/threonine
kinases and protein-tyrosine kinases. Manning et al. [3]
0006-291X/$ - see front matter ? 2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.bbrc.2005.09.150
qAbbreviations: GIST, gastrointestinal stromal tumors; JM, juxtamem-
brane; PDGF, platelet-derived growth factor; pTyr, phosphotyrosine;
PTB, phosphotyrosine binding; SCF, stem cell factor; SH2, Src homology
2; SH3, Src homology 3.
*Fax: +1 504 619 8775.
E-mail address: biocrr@lsuhsc.edu.
www.elsevier.com/locate/ybbrc
Biochemical and Biophysical Research Communications 338 (2005) 1307–1315
BBRC

Page 2

identified 478 typical and 40 atypical protein kinase genes
in humans (total 518) that correspond to about 2% of all
human genes. The family includes 385 protein-serine/thre-
onine kinases, 90 protein-tyrosine kinases, and 43 protein-
tyrosine kinase-like molecules. Of the 90 protein-tyrosine
kinases, a total of 58 are receptor and 32 are non-receptor
in nature. The protein kinase family is the second largest
enzyme family (after proteases) and the fifth largest gene
family in humans [4].
Kit—the stem cell factor receptor
Kit is a type III receptor protein-tyrosine kinase [5] (see
[6] for a description of type I through IX receptor protein-
tyrosine kinases). The type III class also includes the plate-
let-derived growth factor (PDGF) receptor (a- and
b-chains), the macrophage colony-stimulating-factor recep-
tor (CSF-1), and the Fl cytokine receptor (Flt3). Receptor
protein-tyrosine kinases all share the same topology: an
extracellular ligand-binding domain, a single transmem-
brane segment, and a cytoplasmic kinase domain. The class
III receptors are characterized by the presence of five
immunoglobulin-like domains in their extracellular por-
tion. Stem cell factor (SCF) binds to the second and third
immunoglobulin domains while the fourth domain plays
a role in receptor dimerization [7]. The structure of the
class III receptors differs from that of other receptor tyrosyl
kinases by the insertion of 70–100 amino acids near the
middle of the kinase domain. In human Kit, the kinase in-
sert is about 80 residues in length (Fig. 1); this domain
undergoes phosphorylation and serves as a docking site
for a few pivotal signal transduction proteins. The vascular
endothelial growth factor receptor family contains seven
immunoglobulin-like extracellular domains and a kinase
insert like the PDGF receptor family [6].
Kit signaling is important in erythropoiesis, lymphopoi-
esis, mast cell development and function, megakaryopoie-
sis, gametogenesis, and melanogenesis [8]. Stem cells in
both embryos and adults have the unique ability to balance
self-renewal and differentiation such that mature cells nec-
essary for the function of specific organ systems can be
generated and replaced without depletion of the stem cell
pool. The origin of the term stem cell factor referred ini-
tially to its role in survival, self-renewal, and differentiation
of hematopoietic stem cells. However, recent work indi-
cates that the pluripotent R1 mouse embryonic stem cell
line expresses Kit transcripts and functional protein [9].
Using gene arrays and reverse-transcriptase polymerase
chain reactions, Palmqvist et al. [9] found that Kit tran-
scripts decrease to 20% of their initial value 72 h after the
removal of leukemia inhibitory factor (LIF) as mouse
embryonic stem cells lose their pluripotency and become
differentiated. The authors suggest that differentiated cell
types emerge later that re-express Kit. The R1 embryonic
stem cell line does not express SCF, but irradiated mouse
embryo fibroblasts that nourish the cell line in culture ex-
press SCF transcripts.
Stem cell factor and Kit signaling pathways
Binding of SCF to Kit leads to receptor dimerization
and activation of protein kinase activity [10]. The receptor
becomes autophosphorylated at tyrosine residues during
activation; the resulting phosphotyrosine residues serve as
docking sites for signal transduction molecules containing
SH2 and phosphotyrosine-binding (PTB) domains. Acti-
vated Kit also catalyzes the phosphorylation of substrate
proteins.
Kit has the potential to participate in multiple signal
transduction pathways as a result of interacting with sev-
eral enzymes and adaptor proteins [11]. The adaptor pro-
teinAPS, Srcfamilykinases,
phosphatase bind to phosphotyrosine 568. Shp1 tyrosyl
phosphatase and the adaptor protein Shc bind to phos-
photyrosine 570. C-terminal Src kinase homologous ki-
nase (Chk)andthe adaptor
phosphotyrosines 568 and 570. These residues occur in
the juxtamembrane domain of Kit. Three residues in
the kinase insert domain are phosphorylated and attract:
(a) the adaptor protein Grb2 (Tyr703), (b) phosphatidyl-
inositol 3-kinase (Tyr721), and (c) phospholipase Cc
(Tyr730). Phosphotyrosine 900 in the distal kinase do-
main binds phosphatidylinositol 3-kinase that in turn
binds the adaptor protein Crk. Phosphotyrosine 936, also
in the distal kinase domain, binds the adaptor proteins
APS, Grb2, and Grb7 [11].
and Shp2tyrosyl
Shcbind to both
Fig. 1. Organization of Kit. The relative length of the domains is to scale.
The location of Kit gain-of-function mutations is indicated by the residue
numbers on the right hand side of the figure. Ig, immunoglobulin; AL,
activation loop.
1308
R. Roskoski Jr. / Biochemical and Biophysical Research Communications 338 (2005) 1307–1315

Page 3

The numerous Kit interactions cited above lead to acti-
vation of several signal transduction pathways. For exam-
ple, phosphatidylinositol 3-kinase leads to the activation of
Akt. Akt (protein kinase B), a protein-serine/threonine ki-
nase, promotes cell survival [12]. One substrate of Akt is
Bad (Bcl2 antagonist of cell death), a pro-apoptotic protein
that promotes cell death. Following phosphorylation, Bad
no longer promotes apoptosis. Activation of the phospha-
tidylinositol 3-kinase/Akt pathway may explain in part
how activating mutations of Kit participate in neoplastic
transformation. Other downstream effectors of Kit include
the Ras/mitogen-activated protein kinases and the Janus
kinase/signal transducers and activators of transcription
(Jak/STAT) pathways [13].
Overview of Kit protein kinase structure
The Kit protein-tyrosine kinase domain has the charac-
teristic bilobed architecture observed in all protein kinases
(Fig. 2) [14,15]. Residues 582–671 make up the small N-ter-
minal lobe of the kinase, and residues 678-953 make up the
large C-terminal lobe with a hinge segment between them.
The small lobe has a predominantly antiparallel b-sheet
structure and is involved in anchoring and orienting
ATP. It contains a glycine-rich (GAGAFG) ATP-phos-
phate-binding loop composed of residues 596–601. The
large lobe is predominantly a-helical in nature. The large
lobe is responsible for binding the peptide or protein sub-
strate. Furthermore, part of the ATP-binding site occurs
in the large lobe. As described for other protein kinases,
the catalytic site of Kit kinase lies in the cleft between the
small and large lobes [14,15].
The two lobes of protein kinases move relative to each
other and can open or close the cleft [16,17]. The open form
is necessary to allow access of ATP and release of ADP
from the active site; the closed form is necessary to bring
residues into the catalytically active state. Any process that
blocks the interconversion of the open and closed forms of
the cleft will be inhibitory. The juxtamembrane (JM) region
consists of residues 544–581, which lies between the trans-
membrane helix (521–543) and the protein kinase domain
(582–937). As noted below, the JM domain of Kit inhibits
kinase activity, in part, by blocking the relative movement
of the two lobes.
Hanks et al. [18] identified 12 subdomains with con-
served amino acid residue signatures that constitute the
catalytic core of protein kinases. Of these, the following
three amino acids, which define a K/D/D (Lys/Asp/Asp)
motif, illustrate the catalytic properties of Kit. Lys623 is
an invariant residue of protein kinases that forms salt
bridges with the b- and c-phosphates of ATP. Asp792,
the catalytic base, orients the tyrosyl group of the sub-
strate protein in a catalytically competent state and
may abstract a proton from tyrosine thereby facilitating
its nucleophilic attack of the c-phosphorus atom of
MgATP. Asp810 is the first residue of the activation
loop found in the large lobe. The activation loop of
nearly all protein kinases, including Kit, begins with
DFG (810–812) and ends with APE (837–839). Asp810
binds Mg2+, which in turn coordinates the b- and
c-phosphate groups of ATP.
The two kinase lobes can adopt a range of relative
orientations, opening or closing the active-site cleft [16].
Within each lobe is a polypeptide segment that has active
and inactive conformations [16]. In the small lobe, this
segment is the major a-helix. It is designated as the C
a-helix or the aC-helix (where C refers to control). The
aC-helix in some kinases rotates and translates with
Fig. 2. Ribbon diagrams of the activated and autoinhibited forms of Kit showing the N- and C-termini. (A) The C (aC)-helix is in its productive
conformation, and the A (activation) loop is in an extended conformation. The nucleotide is shown as the ball and stick model. (B) The autoinhibitory JM
segment (red) inserts between the N- and C-lobes. The C (aC)-helix is in a dormant conformation, and the A (activation) loop is in a non-extended
conformation. KID, kinase insert domain. The figure is reproduced from [15] with copyright permission from the Journal of Biological Chemistry.
R. Roskoski Jr. / Biochemical and Biophysical Research Communications 338 (2005) 1307–1305
1309

Page 4

respect to the rest of the lobe, making or breaking part
of the catalytic site. In the large lobe, the activation loop
adjusts to make or break part of the protein–substrate-
binding site. In most kinases, including Kit, phosphoryla-
tionoftheactivationloop
conformation.
The catalytic loop surrounding the actual site of
phosphotransfer is different for the protein-serine/threo-
nine and protein-tyrosine kinases [19]. This loop is made
up of RYDLKPEN in protein-serine/threonine kinases
and HRDLAARN in protein-tyrosine kinases including
Kit (His790-Asn797). Asp792 of Kit, which occurs in
the catalytic loop, is the first D of the K/D/D signature
sequence. The AAR sequence in the catalytic loop rep-
resents a receptor protein-tyrosine kinase signature, and
RAA represents a non-receptor protein-tyrosine kinase
signature. Important catalytic and regulatory human
Kit residues are listed in Table 1.
stabilizestheactive
Kit activation by stem cell factor
In the absence of SCF, which is the stimulatory Kit li-
gand, Kit exists in a monomeric dormant state. The general
mechanism for activation of dormant receptor protein-ty-
rosine kinases involves binding of the appropriate ligand
to the extracellular domain of two receptor monomers,
bringing them together, and producing a receptor dimer.
SCF exists as a non-covalent dimer, and this dimer binds
to two Kit monomers thereby promoting Kit dimer forma-
tion [7]. For most receptor protein-tyrosine kinases, dimer
formation is followed by transphosphorylation of 1–3 tyro-
sine residues that occur in the activation loop [16,17]. Such
reactions stabilize the most active enzyme form.
Activation of Kit and the type III receptor protein-
tyrosine kinases is more intricate than that of many
other receptor kinases [20]. The JM segment of Kit is
autoinhibitory, and this additional mechanism for main-
taining a dormant enzyme state must be overcome.
After dimerization, transphosphorylation of two tyrosine
residues (568 and 570) in the autoinhibitory JM segment
occurs [15]. As a result, the JM segment no longer
immobilizes the small and large lobes in a static config-
uration. The activation loop is converted from a com-
pactinactiveconformation
conformation. Transphosphorylation of Tyr823 in the
activation loop stabilizes the active form of the enzyme.
toanextended active
Structure of active Kit
Mol et al. [14,15] determined the structure of an active
and inactive conformation of the human Kit intracellular
domain. The construct contained a truncated kinase in-
sert. The active form of Kit was obtained by incubating
the enzyme with MgATP to initiate the transphosphoryl-
ation reaction. Mass spectrographic analysis of the prod-
ucts revealed that Tyr568 and Tyr570 were the first
residues to be phosphorylated. Thus, autophosphoryla-
tion of residues in the JM domain occurs before that
of the activation loop Tyr823 [15]. This contrasts with
the insulin and insulin-like growth factor receptors where
activation loop phosphorylation occurs first [21]. Howev-
er, it is unclear whether the initial transphosphorylation
of the JM domain of Kit occurs in vivo. Mol et al.
[15] found that Kit transphosphorylation occurs initially
in the JM domain in vitro in a protein lacking the extra-
cellular domain. Perhaps, a different result would be ob-
tained with the complete protein or the complete protein
in a cellular context.
The structure of Kit with ADP, Mg2+, and the side
chain of pTyr568 from an adjacent molecule bound at
the active site is consistent with those of other active
protein kinases [14]. The aC-helix and the activation
loop are in active conformations. A glutamate residue
from the aC-helix (Glu640) forms a salt bridge with
Lys623 (the K of K/D/D) that bridges the a- and b-
phosphates of ADP. Mg2+binds to Asp810 (of the
DFG sequence), Asn797, the phosphate of the phospho-
tyrosine residue that is a product of the transphosphoryl-
ation reaction, and the two phosphates of the ADP
reaction product. Phe811 (of the DFG segment) exists
in its active ‘‘on’’ [15] or ‘‘in’’ [22] conformation that al-
lows the binding of the adenine of ADP. Most of the
residues of the JM segment and the truncated kinase in-
sert domain are disordered.
The activation loop of Kit is in its extended, or active,
conformation even though Tyr823 is unphosphorylated.
When the activation loop is in an extended conforma-
tion, the tyrosine residue is accessible and can be phos-
phorylated in trans by its dimer partner. The R group
of Tyr823 is directed toward arginine 815 and 791. Phos-
phorylation of Tyr823 would further stabilize the extend-
ed conformation of the activation loop and maintain the
enzyme in its active form [14,15].
Table 1
Important amino acid residues in human Kita
Residue or motif
Signal sequence
Extracellular domain
Transmembrane segment
Juxtamembrane domain
JM phosphorylation sites
Protein kinase domain
Glycine-rich nucleotide-binding loop
Phosphate-binding lysine
aC-Helix glutamate
Kinase insert domain
Kinase insert domain phosphorylation sites
Catalytic aspartate
Catalytic loop (HRDLAARN)
Activation loop beginning: DFG
Activation loop end: APE
Activation loop pTyr
C-terminal phosphorylation site
Number of encoded amino acids
1–22
23–520
521–543
544–581
568, 570
582–937
596–601
623
640
685–761
703, 721, 730
792
790–797
810–812
837–839
823
900, 936
976
aSwiss-Prot Accession No. P10721.
1310
R. Roskoski Jr. / Biochemical and Biophysical Research Communications 338 (2005) 1307–1315

Page 5

Structure of inactive Kit
The Kit juxtamembrane domain inhibits kinase activity
in cis. The JM segment of inactive Kit forms a V-shaped
loop that inserts directly into the interface between the
small and large lobes of the kinase (Figs. 2B and 3) [15].
This snapshot of the enzyme suggests that the JM domain
has the potential to inhibit Kit by displacing the aC-helix,
preventing the activation loop from assuming its extended
and active conformation, and preventing the movement of
the small and large lobes necessary for the binding and re-
lease of substrates.
Griffith et al. [24] determined the structure of Flt3, a
type III protein-tyrosine kinase related to Kit. Flt3 is auto-
inhibited by the JM segment by a mechanism which is com-
parable to that observed for Kit. These investigators
divided the JM segment into three topological components:
from the N- to C-direction these are the JM-binding motif
(JM-B), the JM switch (JM-S), and the JM zipper (JM-Z).
The residues in human Kit that correspond to these com-
ponents are 553–559 (JM-B), 560–571 (JM-S), and 572–
581 (JM-Z); these are preceded by residues 544–552, the
JM proximal segment (JM-P). These four components
form a V-shaped structure that lies on the surface of the
Kit kinase domain (Fig. 3).
The JM-B segment, which is nearly buried in Kit, inter-
acts with nearly all structural components implicated in the
activation–inactivation transitions of this enzyme. JM-B
makes contacts with the glycine-rich nucleotide-binding
loop, the activation loop, and the aC-helix. The JM-B seg-
ment constitutes a wedge that stabilizes the inactive kinase
conformation by preventing the small lobe from rotating
toward the large lobe to generate the activated kinase con-
formation. Moreover, JM-B prevents the extension of the
compact, or non-extended, form of the activation loop
from assuming its extended active state. The JM-S segment
contains the two conserved tyrosine residues (568 and 570)
that are the first to be transphosphorylated. The JM-Z is
zippered up against the side of the N-lobe. This segment
has the potential to move away (become unzippered) from
the small lobe; in the active enzyme, the JM-Z segment as-
sumes a disordered state.
Several residues of the JM domain of inactive Kit form
hydrophobic bonds with residues in both the small and
large lobes. Moreover, Tyr553 of the JM segment forms
hydrogen bonds with the side chains of buried and con-
served Asp810 of the DFG segment and Glu640 of the
aC-helix. In the inactive conformation, Phe811 (of the
DFG segment) occurs in its inactive ‘‘off’’ [15] or ‘‘out’’
[22] conformation that prevents the binding of the adenine
of ADP.
The JM domain of inactive Kit sterically blocks the acti-
vation loop from assuming an active conformation. In the
autoinhibited state, the hydroxyl group of non-phosphory-
lated tyrosine 823 forms a hydrogen bond with the catalytic
aspartate (Asp792) thereby preventing the binding of pro-
tein substrates to the active site. In addition, Asp810 of
the DFG segment binds to the positively charged guanidi-
nium group of Arg815 and not to Mg2+.
Kit mutations and human neoplasms
Gain-of-function mutations occur in a percentage of
human neoplasms including mastocytomas (>90%), gas-
trointestinal stromal tumors (>70%), sinonasal T-cell lym-
phomas (17%), seminomas/dysgerminomas (9%), and
acute myelogenous leukemia (1%) [25]. Furthermore,
autocrine or paracrine activation of Kit has been postu-
lated in numerous other human malignancies including
ovarian neoplasms and small-cell lung cancer [25,26]. Fur-
thermore, a large number of human cancers express Kit.
Activating Kit mutations occur in the extracellular, the
JM, and the proximal and distal protein kinase domains
(Fig. 1, Table 2).
Mastocytosis represents a spectrum of rare disorders
that is characterized by mast cell hyperplasia that can in-
volve the skin or a combination of organ systems [28].
Treatment, which includes histamine antagonists, is symp-
tomatic. Mast cell leukemia is a uncommon disorder that is
treated by various non-targeted chemotherapeutic regi-
mens. Seminomas are neoplasms of male germ cells. Local-
ized tumors are treated by surgical resection. Neoplasms
that have spread to other organs are sensitive to radiation
and to a combination of cisplatin and other chemothera-
peutic agents. Most men with advanced cases can be cured
[29]. Dysgerminomas are rare ovarian cancers. Surgical
resection is the mainstay of treatment. In the case of recur-
rence or spread, dysgerminomas are sensitive to radiation
therapy and combination chemotherapy [30]. Nasal T-cell
lymphomas, which are rare, usually affect men in Asia.
Treatment involves surgery, radiation therapy, and con-
Fig. 3. A space-filling diagram of autoinhibited Kit. AL, activation loop;
JM-B, juxtamembrane buried; JM-P, juxtamembrane proximal; JM-S,
juxtamembrane switch; JM-Z, juxtamembrane zipper. Y570-C@O is the
carbonyl oxygen of tyrosine 570. Y570-OH is the phenolic oxygen of
tyrosine 570. In this view, tyrosine 568 is buried. Prepared from protein
database file 1T45. pdb using Protein Explorer [23].
R. Roskoski Jr. / Biochemical and Biophysical Research Communications 338 (2005) 1307–1305
1311