Anchorless adhesins and invasins of Gram-positive bacteria: a new class of virulence factors.

Bacterial adherence to and invasion of eukaryotic cells are important mechanisms of pathogenicity. Most Gram-positive bacteria interact with the components of the host extracellular matrix (ECM) to adhere to, colonize and invade cells and tissues. The bacterial proteins that bind to components of the ECM harbour signal sequences for their secretion and mechanisms of anchoring to the host cell surface. However, in recent years, some cell-surface adhesins and invasins of Gram-positive bacteria have been described that do not possess a signal sequence or a membrane anchor. These proteins are secreted by an as-yet-unknown mechanism and are probably localized on the bacterial surface by reassociation. These anchorless but surface-located adhesins and invasins represent a new class of virulence factors.