Lipid modification of prelipoproteins is dispensable for growth but essential for efficient protein secretion in Bacillus subtilis: characterization of the lgt gene

We have identified and characterized the Igt gene of Bacillus subtilis, The prelipoprotein diacylglycerol transferase enzyme (Lgt) catalyses the first reaction in lipomodification of bacterial lipoproteins. Inactivation of Ig t in B. subtilis by a nonsense mutation (prs-11 mutation) or by disruption was shown here to abolish lipomodification of prelipoproteins completely, a s well as the cleavage of signal peptide. However, unlike in Gram-negative bacteria, the Igf mutants of B. subtilis were fully viable. In agreement wi th this observation, studies of two lipoproteins, PrsA and Slap, indicated that non-lipomodified precursors of these proteins were functional and tran slocated across the cytoplasmic membrane. However, there was release of bot h precursors from cells, resulting in a reduced level of the cell-bound for m. We have shown that the reduced level of the PrsA lipoprotein, a foldase involved in protein secretion, caused impaired protein secretion, a promine nt phenotype of Igt mutants. There was no indication that non-lipomodified PrsA displayed reduced activity.