The N-terminal region of the Oenococcus oeni bacteriophage fOg44 lysin behaves as a bona fide signal peptide in Escherichia coli and as a cis-inhibitory element, preventing lytic activity on oenococcal cells

The function of the N-terminal region of the Oenococcus oeni phage fOg44 ly sin (Lys44) as an export signal was investigated. We observed that when ind uced in Escherichia coli, Lys44 was cleaved between residues 27 and 28 in a SecA-dependent manner. Lys34 processing could be blocked by a specific sig nal peptidase inhibitor and was severely reduced by modification of the cle avage site. The lethal effect of Lys44 expression observed in E, coli was a scribed to the presence of its N-terminal 27-residue sequence, as its delet ion resulted in the production of a nontoxic, albeit active, product. We ha ve further established that lytic activity in oenococcal cells was dependen t on Lys44 processing, An active protein with the molecular mass expected f or the cleaved enzyme was detected in extracts from O, oeni-infected cells. The temporal pattern of its appearance suggests that synthesis and export of Lys44 in the infected host progress along with phage maturation. Overall , these results provide, for the first time, experimental evidence for the presence of a signal peptide in a bacteriophage lysin, Database searches an d alignment of protein sequences support the prediction that other known O, oeni and Lactococcus lactis phages also encode secretory lysins, The evolu tionary significance of a putative phage lysis mechanism relying on secreto ry lytic enzymes is tentatively discussed, on the basis of host cell wall s tructure and autolytic capacity.