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PDBsum entry 2zps
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References listed in PDB file
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Key reference
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Title
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A structural comparison of three isoforms of anionic trypsin from chum salmon (oncorhynchus keta).
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Authors
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E.Toyota,
D.Iyaguchi,
H.Sekizaki,
M.Tateyama,
K.K.Ng.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 2009,
65,
717-723.
[DOI no: ]
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PubMed id
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Abstract
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Three anionic salmon trypsin isoforms (CST-1, CST-2 and CST-3) were isolated
from the pyloric caeca of chum salmon (Oncorhynchus keta). The order of
catalytic efficiency (K(m)/k(cat)) of the isoforms during BAPA hydrolysis was
CST-2 > CST-1 > CST-3. In order to find a structural rationalization for
the observed difference in catalytic efficiency, the X-ray crystallographic
structures of the three isoforms were compared in detail. Some structural
differences were observed in the C-terminal alpha-helix, interdomain loop and
active-site region. From the results of the detailed comparison, it appears that
the structural flexibility of the C-terminal alpha-helix, which interacts with
the N-terminal domain, and the substrate-binding pocket in CST-3 are lower than
those in CST-1 and CST-2. In addition, the conformation of the catalytic triad
(His57, Asp102 and Ser195) differs among the three isoforms. The imidazole N
atom of His57 in CST-1 and CST-2 forms a hydrogen bond to the hydroxyl O atom of
Ser195, but the distance between the imidazole N atom of His57 and the hydroxyl
O atom of Ser195 in CST-3 is too great (3.8 A) for the formation of a hydrogen
bond. Thus, the nucleophilicity of the hydroxyl group of Ser195 in CST-3 is
weaker than that in CST-1 or CST-2. Furthermore, the electrostatic potential of
the substrate-binding pocket in CST-2 is markedly lower than those in CST-1 and
CST-3 owing to the negative charges of Asp150, Asp153 and Glu221B that arise
from the long-range effect. These results may explain the higher catalytic
efficiency of CST-2 compared with CST-1 and CST-3.
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Figure 1.
Figure 1 Superimposition of the C^  atoms
in CST-1, CST-2 and CST-3. The C^ traces
of CST-1, CST-2 and CST-3 are shown in blue, green and red,
respectively. The three catalytic residues (Asp102, His57 and
Ser195), benzamidine and calcium ions are included. The
autolysis loop is shown as a red dashed circle.
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Figure 3.
Figure 3 A comparison of the interactions of the C-terminal
-helix
with the N-terminal domain between the three isozymes. The
interactions of the extremity of the C-terminal -helix
with the N-terminal domain are shown for CST-1 (a), CST-2 (b)
and CST-3 (c). The red dashed lines indicate hydrogen bonds.
Residue numbers are labelled.
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The above figures are
reprinted
by permission from the IUCr:
Acta Crystallogr D Biol Crystallogr
(2009,
65,
717-723)
copyright 2009.
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