Comparative analysis of β-casein proteolysis by PrtP proteinase from Lactobacillus paracasei subsp. paracasei BGHN14, PrtR proteinase from Lactobacillus rhamnosus BGT10 and PrtH proteinase from Lactobacillus helveticus BGRA43

Lactic acid bacteria contain different cell-envelope proteinases responsible for hydrolysis of caseins. Isolates of Lactobacillus paracasei subsp. paracasei BGHN14 and Lactobacillus rhamnosus BGT10 harbour PrtP and PrtR proteinases, respectively, whereas the PrtH proteinase of Lactobacillus helveticus BGRA43 is similar to that of Lb. helveticus CNRZ32. Mass spectrometry analysis of the major peptides isolated by reversed phase-high performance liquid chromatography allowed the identification of 25, 22 and 17 peptides after β-casein hydrolysis by strains BGHN14, BGRA43 and BGT10, respectively. Regardless of the type of proteinase, β-casein was hydrolyzed preferentially after hydrophobic residues and glutamines (Q). PrtP and PrtR proteinases preferentially targeted the C-terminus of β-casein. In the case of PrtH proteinase, most of the peptides obtained were cleaved from N-terminus of this casein. Nine identical peptides were identified after hydrolysis with PrtP and PrtR, three after proteolysis with PrtR and PrtH, and two after hydrolysis with all three proteinases studied.