Autolysins of Bacillus subtilis: multiple enzymes with multiple functions.

Autolysins are bacteriolytic enzymes that digest the cellwall peptidoglycan of the bacteria that produce them (Shockman&Ho$ ltje, 1994). Although potentially lethal, autolysins appear to be universal among bacteria that possess peptidoglycan. Peptidoglycan, the substrate of autolysins, is a polymer of amino sugars cross-linked by short peptides which forms a covalent matrix that surrounds the cytoplasmic membrane and constitutes the major skeletal component of the cell wall. It is critical in determining cell shape and preventing osmotic lysis under hypotonic conditions. Cell-wall peptidoglycan, whilst very strong, is also highly dynamic: the structure expands as the cell grows and is reshaped when it divides or differentiates. The possibility that autolysins are involved in selective removal of peptidoglycan has led to proposals that they are involved in numerous cellular processes including cell growth, cell-wall turnover, peptidoglycan maturation, cell division, separation, motility, chemotaxis, genetic competence, protein secretion, differentiation and pathogenicity (Foster, 1994; Blackman et al., 1998).