Role of the YadA protein in prevention of opsonization of Yersinia enterocolitica by C3b molecules.

When mixed with normal human serum, wild-type pathogenic Yersinia enterocolitica, previously incubated at 37 degrees C, fixed less C3b than its variant cured of the virulence plasmid pYV. Mutants unable to secrete the Yop proteins were still protected against C3b deposition. By contrast, mutants deficient in the production of outer membrane protein YadA fixed more C3b than their YadA+ parent. Gene yadA, cloned as a minimal polymerase chain reaction fragment and introduced in trans, complemented the mutations. Production of YadA by recombinant Escherichia coli LK111 also resulted in a reduction of the amount of C3b deposited on the bacterial surface. The reduction of C3b at the surface of Y. enterocolitica YadA+ compared with YadA- cells correlated with an increase of the amount of factor H fixed at the bacterial surface. The YadA monomer separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred to a nitrocellulose membrane was able to bind factor H. We conclude that factor H bound to YadA reduces the C3b deposition on the bacterial surface, probably by a rapid inactivation of C3b.