Evidence that Mycobacterial PE_PGRS Proteins Are Cell Surface Constituents That Influence Interactions with Other Cells

Abstract

The elucidation of the genomic sequence ofMycobacterium tuberculosisrevealed the presence of a novel multigene family designated PE/PE_PGRS that encodes numerous, highly related proteins of unknown function. In this study, we demonstrate that a transposon insertion in a PE_PGRS gene (1818^PE_PGRS) found inMycobacterium bovisBCG Pasteur, which is the BCG homologue of theM.tuberculosisH37Rv geneRv1818c, introduces new phenotypic properties to this BCG strain. These properties include dispersed growth in liquid medium and reduced infection of macrophages. Complementation of the 1818^PE_PGRS::Tn5367mutant with the wild-type gene restores both aggregative growth (clumping) in liquid medium and reestablishes infectivity of macrophages to levels equivalent to those for the parent BCG strain. Western blot analysis using antisera raised against the 1818^PE_PGRSprotein shows that PE_PGRS proteins are found in cell lysates of BCG andM.tuberculosisH37Ra and in the cell wall fraction ofM.tuberculosisH37Rv. Moreover, immunofluorescent labeling of mycobacteria indicates that certain PE_PGRS proteins are localized at the cell surface of BCG andM.tuberculosis. Together these results suggest that certain PE_PGRS proteins may be found at the surface of mycobacteria and influence both cell surface interactions among mycobacteria as well as the interactions of mycobacteria with macrophages.