Phosphorylation of tyrosine 474 of the enteropathogenic Escherichia coli (EPEC) Tir receptor molecule is essential for actin nucleating activity and is preceded by additional host modifications
B. Kenny, Phosphorylation of tyrosine 474 of the enteropathogenic Escherichia coli (EPEC) Tir receptor molecule is essential for actin nucleating activity and is preceded by additional host modifications, MOL MICROB, 31(4), 1999, pp. 1229-1241
The enteropathogenic Escherichia coli (EPEC) Tir protein becomes tyrosine p
hosphorylated in host cells and displays an increase in apparent molecular
mass. The interaction of Tir with the EPEC outer membrane protein, intimin,
triggers actin nucleation beneath the adherent bacteria. The enterohaemorr
hagic E. coli 0157:H7 (EHEC) Tir molecule is not tyrosine phosphorylated. I
n this paper, Tir tyrosine phosphorylation is shown to be essential for act
in nucleation activity, but not for the increase in apparent molecular mass
observed in target cells. Tyrosine phosphorylation had no role in Tir mole
cular mass shift, indicating additional host modifications. Analysis of Tir
intermediates indicates that tyrosine-independent modification functions t
o direct Tir's correct insertion from the cytoplasm into the host membrane.
Deletion analysis identified Tir domains participating in translocation, a
ssociation with the host membrane, modification and antibody recognition. I
ntimin was found to bind a 55-amino-acid region (TIBA) within Tir that topo
logical and sequence analysis suggests is located in an extracellular loop.
Homologous TIBA sequences exist in integrins, which also bind intimin. Col
lectively, this study provides definitive evidence for the importance of ty
rosine phosphorylation for EPEC Tir function and reveals differences in the
pathogenicity of EPEC and EHEC, The data also suggest a mechanism for Tir
insertion into the host membrane, as well as providing clues to the mode of
intimin-integrin interaction.