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Cooperation between actin‐binding proteins of invasive Salmonella: SipA potentiates SipC nucleation and bundling of actin

Emma J. McGhie, Richard D. Hayward, Vassilis Koronakis

Author Affiliations

  1. Emma J. McGhie1,
  2. Richard D. Hayward1 and
  3. Vassilis Koronakis*,1
  1. 1 Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
  1. *Corresponding author. E-mail: vk103{at}mole.bio.cam.ac.uk
  1. E.J.McGhie and R.D.Hayward contributed equally to this work

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Abstract

Pathogen‐induced remodelling of the host cell actin cytoskeleton drives internalization of invasive Salmonella by non‐phagocytic intestinal epithelial cells. Two Salmonella actin‐binding proteins are involved in internalization: SipC is essential for the process, while SipA enhances its efficiency. Using purified SipC and SipA proteins in in vitro assays of actin dynamics and F‐actin bundling, we demonstrate that SipA stimulates substantially SipC‐mediated nucleation of actin polymerization. SipA additionally enhances SipC‐ mediated F‐actin bundling, and SipC–SipA collaboration generates stable networks of F‐actin bundles. The data show that bacterial SipC and SipA cooperate to direct efficient modulation of actin dynamics, independently of host cell proteins. The ability of SipA to enhance SipC‐induced reorganization of the actin cytoskeleton in vivo was confirmed using semi‐ permeabilized cultured mammalian cells.

  • Received November 14, 2000.
  • Revision received March 6, 2001.
  • Accepted March 6, 2001.
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