INIB - AN INVASION PROTEIN OF LISTERIA-MONOCYTOGENES WITH A NOVEL TYPE OF SURFACE ASSOCIATION

Listeria monocytogenes is an intracellular bacterial pathogen that exp resses several surface proteins critical for the infectious process, S uch proteins include InIA (internalin) and InIB, involved in bacterial entry into the host cell, and ActA, required for bacterially induced actin-based motility, Although the molecular mechanisms of attachment of InIA and ActA have been characterized, essentially nothing is known about how InIB is anchored to the bacterial surface, Using a genetic approach, we demonstrate that the last 232 amino acids of InIB are bot h necessary and sufficient for anchoring this protein to the bacterial surface, An InIB mutant protein deleted for the last 232 amino acids was secreted and not detected at the cell surface, A 'domain-swapping' strategy in which these 232 amino acids were used to replace the norm al cell wall-anchoring domain of InIA resulted in a chimeric protein t hat was anchored to the cell surface and able to confer entry, Interes tingly, surface association of InIB also occurred when InIB was added externally to bacteria, suggesting that association may be able to occ ur after secretion, This association was productive for invasion, as i t conferred bacterial entry into host cells, The C-terminal anchoring region in InIB contains 80-amino-acid repeats beginning with the seque nce GW that is also present in a newly identified surface-associated b acteriolysin of L. monocytogenes, called Ami, Addition of GW repeats t o the C-terminal of InIB improves anchoring of the protein to the cell surface, These and other data suggest that such 'GW' repeats may cons titute a novel motif for cell-surface anchoring in Listeria and other Gram-positive bacteria, This motif may have important consequences for the release of surface proteins involved in interactions with eukaryo tic cells.