BbrPI, an extracellular proteinase inhibitor of Bacillus brevis, protects cells from the attack of exogenous proteinase.

BbrPI, an extracellular serine proteinase inhibitors of B. brevis HPD31, is activated by proteolytic processing of an inactive precursor. To discover the physiological role of BbrPI, its deficient mutants were genetically constructed. Although the BbrPI deficient mutant had a higher extracellular proteinase activity than the parent strain, it grew normally. The BbrPI deficient mutant showed higher sensitivity to added trypsin than that of the parent. These observations suggest that the BbrPI may play a role in cellular protection from the attack of exogenous proteinases.