Variation in specificity of the PrtP extracellular proteinases in Lactococcus lactis and Lactobacillus paracasei subsp. paracasei

Comparison of cell-wall-bound extracellular proteinases (CEPs) from Lactobacillus paracasei (LBP) ssp. paracasei natural isolates BGHN14, BGAR75 and BGAR76 with Lactococcus lactis (LCL) ssp. cremoris Wg2, in their action on αS1-, β- and κ-casein was done. The CEPs of LBP strains were able to degrade αS1- and β-caseins and their caseinolytic specificity depended on the type of buffer used. These CEPs, compared with LCL Wg2, differ in four amino acid residues in small segments predicted to be involved in substrate binding. The most striking features of this comparison are the presence of Ala instead of Ser329 and the presence of Thr instead of Asn256 and Ala299, in the subtilisin-like region of the CEP in LBP natural isolates. Additional conservative amino acid substitution Leu to Ile364 was found.