PDBsum entry 1xg6

Hydrolase inhibitor

PDB id: 1xg6

Contents

Protein chain

179 a.a. *

Waters ×190

* Residue conservation analysis

PDB id:

1xg6

Name:

Hydrolase inhibitor

Title:

The crystal structure of the p1 mutant (leu to arg)of a winged bean chymotrypsin inhibitor(kunitz)solved at 2.15a resolution

Structure:

Chymotrypsin inhibitor 3. Chain: a. Synonym: winged bean chymotrypsin inhibitor, wci-3. Engineered: yes. Mutation: yes

Source:

Psophocarpus tetragonolobus. Winged bean. Organism_taxid: 3891. Expressed in: escherichia coli. Expression_system_taxid: 562.

Resolution:

2.15Å R-factor: 0.199 R-free: 0.236

Authors:

U.Sen,J.K.Dattagupta,J.Dasgupta,S.Khamrui

Key ref:

S.Khamrui et al. (2005). Single mutation at P1 of a chymotrypsin inhibitor changes it to a trypsin inhibitor: X-ray structural (2.15 A) and biochemical basis. Biochim Biophys Acta, 1752, 65-72. PubMed id: 16081330

Date:

16-Sep-04 Release date: 30-Aug-05

Protein chain

P10822  (ICW3_PSOTE) -  Chymotrypsin inhibitor 3 from Psophocarpus tetragonolobus

Seq: 207 a.a.

Struc: 179 a.a.*

* PDB and UniProt seqs differ at 4 residue positions (black crosses)

Biochim Biophys Acta 1752:65-72 (2005)

PubMed id: 16081330

Single mutation at P1 of a chymotrypsin inhibitor changes it to a trypsin inhibitor: X-ray structural (2.15 A) and biochemical basis.

S.Khamrui, J.Dasgupta, J.K.Dattagupta, U.Sen.

ABSTRACT

Change in specificity, caused by the mutations at P1 site, of the serine protease inhibitors of different families is reported in the literature, but Kunitz (STI) family inhibitors are almost unexplored in this regard. In this paper, we present the crystal structure of a P1 variant of winged bean chymotrypsin inhibitor (WCI) belonging to Kunitz (STI) family, supplemented by biochemical, phylogenetic and docking studies on the mutant. A single mutation (Leu-->Arg) at P1 converted WCI to a strong inhibitor of trypsin with an association constant of 4.8x10(10) M(-1) which is comparable to other potent trypsin inhibitors of the family. The crystal structure (2.15 A) of this mutant (L65R) shows that its reactive site loop conformation deviates from that of WCI and adopts a structure similar to that of Erythrina caffra trypsin inhibitor (ETI) belonging to the same family. Mutation induced structural changes have also been propagated in a concerted manner to the neighboring conserved scaffolding residue Asn14, such that the side chain of this residue took an orientation similar to that of ETI and optimized the hydrogen bonds with the loop residues. While docking studies provide information about the accommodation of non-specific residues in the active site groove of trypsin, the basis of the directional alteration of the reactive site loop conformation has been understood through sequence analysis and related phylogenetic studies.