Biophysical characterization of SipA, an actin-binding protein from Salmonella enterica

An essential step in the pathogenesis of Salmonella enterica infections is bacterial entry into non-phagocytic cells of the intestinal epithelium. Pro teins injected by Salmonella into host cells stimulate cellular responses t hat lead to extensive actin cytoskeleton reorganization and subsequent bact erial uptake, One of these proteins, SipA, modulates actin dynamics by dire ctly binding to F-actin, We have biophysically, characterized a C-terminal fragment, SipA(446-684), which has previously been shown to retain activity , Our results show that SipA(446-684) exhibits an elongated shape with a pr edominantly helical conformation and predict the existence of a coiled-coil domain. We suggest that the protein is able to span two adjacent actin mon omers in a filament and propose a model that is consistent with the observe d effects of SipA(446-684) on actin dynamics and F-actin stability and morp hology. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.