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PDBsum entry 1bzx
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Hydrolase/hydrolase inhibitor
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PDB id
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1bzx
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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The crystal structure of anionic salmon trypsin in complex with bovine pancreatic trypsin inhibitor.
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Authors
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R.Helland,
I.Leiros,
G.I.Berglund,
N.P.Willassen,
A.O.Smalås.
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Ref.
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Eur J Biochem, 1998,
256,
317-324.
[DOI no: ]
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PubMed id
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Abstract
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The complex formed between anionic salmon trypsin (ST) and bovine pancreatic
trypsin inhibitor (BPTI) has been crystallised, and the X-ray structure has been
solved using the molecular replacement method. The crystals are hexagonal and
belong to space group P6(1)22 with lattice parameters of a = b = 83.12 A and c =
222.15 A. Data have been collected to 2.1 A and the structure has been refined
to a crystallographic R-factor of 20.6%. Catalysis by salmon trypsin is
distinguished by a Km value 20-fold lower than that for mammalian trypsins, and
a k(cat) twice as high. The present ST-BPTI complex serves as a model for the
Michaelis-Menten complex, and has been compared with corresponding bovine and
rat trypsin (RT) complexes. The binding of BPTI to salmon trypsin is
characterised by stronger primary interactions in the active site, and a
somewhat looser secondary binding.
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Figure 3.
Fig. 3. Primary and secondary binding. Stereo plot of the primary and secondary binding of the BPTI (blue) to anionic salmon trypsin (red). The
N
#
atom of P1 lysine contacts the carboxylate group of Asp189 through one direct hydrogen bond to O
#2
and through a water molecule to O
#1
. Five
hydrogen bonds, which all contact the inhibitor main chain, are conserved in the secondary binding sites of all three complexes. Two are on the N
terminal side of the scissile bond, and three on the Cterminal side. Additional hydrogen bonds are formed between inhibitor side chains and the
enyme (see Table 4 for further details). The figure was prepared using BOBSCRIPT [33, 34].
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Figure 5.
Fig. 5. Electrostatic surface potentials of trypsins. Electrostatic potential of the surfaces of salmon (left), bovine (middle) and rat (right) trypsins.
Potentials are taken from the PDB files. The P3P4˘ binding loops of BPTI illustrates the binding of Lys15I in the specificity pockets and the
different orientations of the Arg17I side chain (to the right). The figure also shows that the binding cleft of salmon trypsin is more open than for
the mammalian enzymes due to the different fold of the autolysis loop. The figure was prepared using GRASP [37].
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The above figures are
reprinted
by permission from the Federation of European Biochemical Societies:
Eur J Biochem
(1998,
256,
317-324)
copyright 1998.
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