Redesigning the reactive site loop of the wheat subtilisin/chymotrypsin inhibitor (WSCI) by site-directed mutagenesis. A protein-protein interaction study by affinity chromatography and molecular modeling

Natalia Bruni, Antimo Di Maro, Susan Costantini, Angela Chambery, Angelo M. Facchiano, Anna Grazia Ficca, Augusto Parente, Elia Poerio

Research output: Contribution to journalArticle

Abstract

A site-directed mutagenesis strategy was employed to obtain four mutants of wheat subtilisin/chymotrypsin inhibitor (WSCI), with the aim to produce inactive forms of this protein. The mutants were expressed in Escherichia coli as fusion proteins and, after the tag removal, were purified to homogeneity. Three mutants, containing a single mutation at the sequence positions 49 or 50, were named E49S, E49P and Y50G, respectively. These mutants exhibited anti-subtilisin activities comparable to that of the wild type protein; instead, anti-chymotrypsin activity was detectable only for the mutant E49S. A fourth mutant (M48P-E49G), containing a double amino acid substitution at the inhibitor reactive site (P1-P1′), was inactive against both subtilisin and chymotrypsin. In order to investigate the interactions between the putative susceptible enzymes and the mutated forms of WSCI, we performed time-course hydrolysis experiments by incubating samples of the mutants with subtilisin-agarose and chymotrypsin-agarose, respectively. These experiments yielded information on the E/I complex formation, as well as on the timing of the cleavage pattern of some of these mutants. Molecular modeling studies were carried out with the 3D models of the mutants and of their putative complexes with subtilisin and chymotrypsin. In terms of inter- and intra-chain H-bond networks, the observations made for each theoretical E/I complex were found to be fully coherent with experimental data (kinetic and time-course hydrolysis) and supplied specific modalities of interaction of each mutant with the enzyme counterpart.

Original languageEnglish
Pages (from-to)1112-1122
Number of pages11
JournalBiochimie
Volume91
Issue number9
DOIs
Publication statusPublished - Sep 2009

Keywords

  • E/I complexes
  • ESI Q-TOF mass spectrometry
  • Time-course proteolysis
  • WSCI mutants

ASJC Scopus subject areas

  • Biochemistry

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