Genetic characterization of a cell envelope-associated proteinase from Lactobacillus helveticus CNRZ32

A cell envelope-associated proteinase gene (prtH) was identified in Lactoba cillus helveticus CNRZ32. The prtH gene encodes a protein of 1,849 amino ac ids and with a predicted molecular mass of 204 kDa, The deduced amino acid sequence of the prtH product has significant identity (45%) to that of the lactococcal PrtP proteinases. Southern blot analysis indicates that prtH is not broadly distributed within L. helveticus, A prtH deletion mutant of CN RZ32 was constructed to evaluate the physiological role of PrtH. PrtH is no t required for rapid growth or Fast acid production in milk by CNRZ32, Cell surface proteinase activity and specificity were determined by hydrolysis of alpha(s1)-casein fragment 1-23 by whole cells. A comparison of CNRZ32 an d its prtH deletion mutant indicates that CNRZ32 has at least two cell surf ace proteinases that differ in substrate specificity.