Nck-independent actin assembly is mediated by two phosphorylated tyrosines within enteropathogenic Escherichia coli Tir

UMMS Affiliation

Graduate School of Biomedical Sciences; Department of Molecular Genetics and Microbiology

Publication Date


Document Type



Life Sciences | Medicine and Health Sciences


Enteropathogenic Escherichia coli (EPEC) stimulates tyrosine-kinase signalling cascades to trigger localized actin assembly within mammalian cells. During actin 'pedestal' formation, the EPEC effector protein Tir is translocated into the plasma membrane, becomes phosphorylated on tyrosine-474 (Y474) and promotes recruitment of the mammalian adaptor protein Nck to efficiently activate N-WASP-Arp2/3-mediated actin polymerization. Tir also triggers localized actin assembly in the absence of Nck, but the Tir sequences involved in this signalling cascade have not been defined. To identify and characterize the phosphotyrosines that contribute to Nck-independent pedestal formation, we investigated the regulation of Tir tyrosine phosphorylation and found that phosphorylation is stimulated by Tir clustering. In addition to Y474, residue Y454 is also phosphorylated, although at lower efficiency. These tyrosines differentially contribute to actin polymerization in a fashion reminiscent of actin 'tail' formation mediated by the vaccinia virus envelope protein A36R, which utilizes two similarly spaced phosphotyrosines to recruit the adaptors Nck and Grb2, respectively, in order to stimulate N-WASP. Neither phosphorylated Y454 nor Y474 directly bind Grb2, but Tir derivatives harbouring these residues ultimately recruit N-WASP and Arp2/3 independently of Nck, suggesting that EPEC exploits additional phosphotyrosine-binding adaptors capable of initiating actin assembly.

DOI of Published Version



Mol Microbiol. 2005 Apr;56(2):416-32. Link to article on publisher's site

Journal/Book/Conference Title

Molecular microbiology

Related Resources

Link to article in PubMed

PubMed ID