Lipoprotein signal peptides are processed by Lsp and Eep of Streptococcus uberis

Institute for Animal Health, Compton, Berkshire, RG20 7NN; Nuffield Department of Clinical Laboratory Sciences, Oxford University, John Radcliffe Hospital, Headington, OX3 9DU, UK; School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington, Leicestershire, LE12 5RD, UK

	Abstract

Lipoprotein signal peptidase (lsp) is responsible for cleaving the signal peptide sequence of lipoproteins in Gram positive bacteria. Investigation of the role of Lsp in S. uberis, a common cause of bovine mastitis, was undertaken using the lipoprotein MtuA (a protein essential for virulence) as a marker. The S. uberis lsp mutant phenotype displayed novel lipoprotein processing. Not only was full length (uncleaved) MtuA detected by Western blot, but during late log phase, a lower molecular weight derivative of MtuA was evident. Similar analysis of a S. uberis double mutant, containing insertions disrupting both lsp and eep (a homologue of the Enterococcus faecalis "enhanced expression of pheromone") indicated a role for eep in cleavage of lipoproteins in the absence of Lsp. Such a function may indicate a role for eep in maintenance of secretion pathways during disruption of normal lipoprotein processing.