title: Changes in protein structure at the interface accompanying complex formation.
abstract: Protein interactions are essential in all biological processes. The changes brought about in the structure when a free component forms a complex with another molecule need to be characterized for a proper understanding of molecular recognition as well as for the successful implementation of docking algorithms. Here, unbound (U) and bound (B) forms of protein structures from the Protein-Protein Interaction Affinity Database are compared in order to enumerate the changes that occur at the interface atoms/residues in terms of the solvent-accessible surface area (ASA), secondary structure, temperature factors (B factors) and disorder-to-order transitions. It is found that the interface atoms optimize contacts with the atoms in the partner protein, which leads to an increase in their ASA in the bound interface in the majority (69%) of the proteins when compared with the unbound interface, and this is independent of the root-mean-square deviation between the U and B forms. Changes in secondary structure during the transition indicate a likely extension of helices and strands at the expense of turns and coils. A reduction in flexibility during complex formation is reflected in the decrease in B factors of the interface residues on going from the U form to the B form. There is, however, no distinction in flexibility between the interface and the surface in the monomeric structure, thereby highlighting the potential problem of using B factors for the prediction of binding sites in the unbound form for docking another protein. 16% of the proteins have missing (disordered) residues in the U form which are observed (ordered) in the B form, mostly with an irregular conformation; the data set also shows differences in the composition of interface and non-interface residues in the disordered polypeptide segments as well as differences in their surface burial.
authors.affiliation: Department of Biochemistry, Bose Institute , P-1/12 CIT Scheme VIIM, Kolkata 700 054, India.
authors.forename: Devlina
authors.initials: D
authors.lastname: Chakravarty
authors.affiliation: IBBMC, CNRS UMR 8619, Universite Paris-Sud 11 , Orsay, France.
authors.forename: Joël
authors.initials: J
authors.lastname: Janin
authors.affiliation: CNRS Laboratoire de Biochimie Theorique, Institut de Biologie Physico-Chimique (IBPC), Universite Paris Diderot, Sorbonne Paris Cité , 13 Rue Pierre et Marie Curie, 75005 Paris, France.
authors.forename: Charles H
authors.initials: CH
authors.lastname: Robert
authors.affiliation: Department of Biochemistry, Bose Institute , P-1/12 CIT Scheme VIIM, Kolkata 700 054, India.
authors.forename: Pinak
authors.initials: P
authors.lastname: Chakrabarti
keywords: bioinformatics; bound and unbound protein forms; crystallographic temperature factor; disorder–order transition; interface area; molecular recognition; protein flexibility; protein–protein interactions; secondary structure