A NEW CELL-SURFACE PROTEINASE - SEQUENCING AND ANALYSIS OF THE PRTB GENE FROM LACTOBACILLUS-DELBRUECKII SUBSP BULGARICUS

Investigation of the chromosomal region downstream of the lacZ gene fr om Lactobacillus delbrueckii subsp. bulgaricus revealed the presence o f a gene (prtB) encoding a proteinase of 1,946 residues with a predict ed molecular mass of 212 kDa. The deduced amino acid sequence showed t hat PrtB proteinase displays significant homology with the N termini a nd catalytic domains of lactococcal PrtP cell surface proteinases and is probably synthesized as a preproprotein. However, the presence of a cysteine near the histidine Of the PrtB active site suggests that Prt B belongs to the subfamily of cysteine subtilisins. The C-terminal reg ion strongly differs from those of PrtP proteinases by having a high l ysine content, an imperfect duplication of 41 residues, and a degenera ted sequence compared with the consensus sequence for proteins anchori ng in the cell walls of gram-positive bacteria. Finally, the product o f the truncated prtM-like gene located immediately upstream of the prt B gene seems too short to be involved in the maturation of PrtB.