Active Lipoprotein Precursors in the Gram-positive EubacteriumLactococcus lactis

Abstract

Lipid-modified proteins play important roles at the interface between eubacterial cells and their environment. The importance of lipoprotein processing by signal peptidase II (SPase II) is underscored by the fact that this enzyme is essential for viability of the Gramnegative eubacterium Escherichia coli. In contrast, SPase II is not essential for growth and viability of the Gram-positive eubacterium Bacillus subtilis. This could be due to alternative amino-terminal lipoprotein processing, which was shown previously to occur in SPase II mutants of B. subtilis. Alternatively, uncleaved lipoprotein precursors might be functional. To explore further the importance of lipoprotein processing in Gram-positive eubacteria, an SPase II mutant strain of Lactococcus lactis was constructed. Although some of the 39 (predicted) lactococcal lipoproteins, such as PrtM and OppA, are essential for growth in milk, the growth of SPase II mutant L. lactis cells in this medium was not affected. Furthermore, the activity of the strictly PrtMdependent extracellular protease PrtP, which is required for casein degradation, was not impaired in the absence of SPase II. Importantly, no alternative processing of pre-PrtM and pre-OppA was observed in cells lacking SPase II. Taken together, these findings show for the first time that authentic lipoprotein precursors retain biological activity.

An Important Step inListeriaLipoprotein Research

“…Similar to Lgt, the lipoprotein-specific signal peptidase Lsp has been shown to be dispensable for growth in several grampositive bacteria, including L. monocytogenes (6,13,21,23). These findings contrast with those obtained for gram-negative bacteria, in which both Lgt and Lsp are essential enzymes.…”

Maturation of Lipoproteins by Type II Signal Peptidase Is Required for Phagosomal Escape of Listeria monocytogenes

“…No alternative processing of these precursors occurs in the absence of this SPase II. Unprocessed lactoccocal lipoprotein precursors kept their biological activity (37). In L. monocytogenes, the lack of Lsp did not impair growth in broth, including at 4°C.…”

“…For example, unlike the SPase II of E. coli (35), the SPase II of B. subtilis and Lactococcus lactis are not essential for growth and viability (36,37). However, in these non-pathogenic species, the absence of SPase II resulted in cold and heat sensitivity.…”

Lipoprotein biogenesis in Gram-positive bacteria: knowing when to hold ‘em, knowing when to fold ‘em

“…Likewise, the lipoproteins PrtM and OppA of Lactococcus lactis are needed for growth of this organism in milk and yet an L. lactis lsp mutant can grow in milk [35].…”