PDBsum entry 1jc6

Toxin

PDB id: 1jc6

Contents

Protein chain

65 a.a. *

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Solution structure of a kunitz-Type chymotrypsin inhibitor isolated from the elapid snake bungarus fasciatus.

Authors

C.Chen, C.H.Hsu, N.Y.Su, Y.C.Lin, S.H.Chiou, S.H.Wu.

Ref.

J Biol Chem, 2001, 276, 45079-45087. [DOI no: 10.1074/jbc.M106182200]

PubMed id

11562364

Abstract

Bungarus fasciatus fraction IX (BF9), a chymotrypsin inhibitor, consists of 65 amino acid residues with three disulfide bridges. It was isolated from the snake venom of B. fasciatus by ion-exchange chromatography and belongs to the bovine pancreatic trypsin inhibitor (BPTI)-like superfamily. It showed a dissociation constant of 5.8 x 10(-8) m with alpha-chymotrypsin as measured by a BIAcore binding assay system. The isothermal titration calorimetry revealed a 1:1 binding stoichiometry between this inhibitor and chymotrypsin and apparently no binding with trypsin. We further used CD and NMR to determine the solution structure of this venom-derived chymotrypsin inhibitor. The three-dimensional NMR solution structures of BF9 were determined on the basis of 582 restraints by simulated annealing and energy minimization calculations. The final set of 10 NMR structures was well defined, with average root mean square deviations of 0.47 A for the backbone atoms in the secondary structure regions and 0.86 A for residues The side chains of Phe(23), Tyr(24), Tyr(25), Phe(35), and Phe(47) exhibited many long-range nuclear Overhauser effects and were the principal components of the hydrophobic core in BF9. To gain insight into the structure-function relationships among proteins in the BPTI-like superfamily, we compared the three-dimensional structure of BF9 with three BPTI-like proteins that possess distinct biological functions. These proteins possessed similar secondary structure elements, but the loop regions and beta-turn were different from one another. Based on residues at the functional site of each protein, we suggest that the flexibility, rigidity, and variations of the amino acid residues in both the loop and beta-turn regions are related to their biological functions.

Figure 2.
Fig. 2. Representative overlaid sensorgram for kinetic study of -chymotrypsin binding to BF9 measured by a BIAcore X system. BF9 was immobilized on a CM5 sensor chip by amine coupling. The -chymotrypsin was injected over the sensor chip at concentrations ranging from 10 to 500 nM: trace a, 10 nM; trace b, 30 nM; trace c, 50 nM; trace d, 100 nM; trace e, 200 nM; trace f, 300 nM; trace g, 400 nM; trace h, 500 nM. Raw binding data were analyzed by BIAevaluation Version 3.0 Software and fit to a 1:1 Langmuir binding model. RU, response units.

Figure 9.
Fig. 9. Ramachandran plot of and dihedral angles for the ensemble of 10 NMR structures of BF9 generated using the PROCHECK-NMR program. Triangles in the plots represent the angles for glycine residues.

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2001, 276, 45079-45087) copyright 2001.

Secondary reference #1

Title

Complete amino acid sequences of two protease inhibitors in the venom of bungarus fasciatus.

Authors

C.S.Liu, T.C.Wu, T.B.Lo.

Ref.

Int J Pept Protein Res, 1983, 21, 209-215.

PubMed id

6832893