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PDBsum entry 2qxg
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References listed in PDB file
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Key reference
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Title
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Chymotryptic specificity determinants in the 1.0 a structure of the zinc-Inhibited human tissue kallikrein 7.
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Authors
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M.Debela,
P.Hess,
V.Magdolen,
N.M.Schechter,
T.Steiner,
R.Huber,
W.Bode,
P.Goettig.
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Ref.
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Proc Natl Acad Sci U S A, 2007,
104,
16086-16091.
[DOI no: ]
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PubMed id
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Abstract
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hK7 or human stratum corneum chymotryptic enzyme belongs to the human tissue
kallikrein (hKs) serine proteinase family and is strongly expressed in the upper
layers of the epidermis. It participates in skin desquamation but is also
implicated in diverse skin diseases and is a potential biomarker of ovarian
cancer. We have solved x-ray structures of recombinant active hK7 at medium and
atomic resolution in the presence of the inhibitors
succinyl-Ala-Ala-Pro-Phe-chloromethyl ketone and Ala-Ala-Phe-chloromethyl
ketone. The most distinguishing features of hK7 are the short 70-80 loop and the
unique S1 pocket, which prefers P1 Tyr residues, as shown by kinetic data.
Similar to several other kallikreins, the enzyme activity is inhibited by Zn(2+)
and Cu(2+) at low micromolar concentrations. Biochemical analyses of the mutants
H99A and H41F confirm that only the metal-binding site at His(99) close to the
catalytic triad accounts for the noncompetitive Zn(2+) inhibition type.
Additionally, hK7 exhibits large positively charged surface patches,
representing putative exosites for prime side substrate recognition.
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Figure 4.
Fig. 4. Stick model of the modeled substrate
Glu-Ala-Leu-Tyr-Leu-Val, the catalytic triad and the backbone of
Gly^193, Ser^195, and Gly^216 of hK7[I] in stereo, including
hydrogen bonds as dotted lines. The S1 pocket is depicted as
transparent green surface according to volume calculations with
VOIDOO (41). The specificity for P1 Tyr is most likely conferred
by Asn^189 via hydrogen bonds from the carboxamide side chain to
an interconnecting water molecule and to the Tyr OH group,
respectively.
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Figure 5.
Fig. 5. The copper ions bound at His^99 and His^41
displayed as blue spheres surrounded by electron density of the
anomalous Fourier map in red (contour 5  ) in stereo. His^57 has
the capacity for liganding Cu1 and Cu2 by a side chain rotation
(His57*), requiring shifts of the ions, whereas the mutant H99A
proves that only the His^99 site is the structural basis for the
Zn^2+ and Cu^2+ inhibition of hK7.
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