Role of the unique, non-essential phosphatidylglycerol::prolipoprotein diacylglyceryl transferase (Lgt) in Corynebacterium glutamicum

Abstract

Bacterial lipoproteins are secreted proteins that are post-translationally lipidated. Following synthesis, preprolipoproteins are transported through the cytoplasmic membrane via the Sec or Tat translocon. As they exit the transport machinery, they are recognized by a phosphatidylglycerol::prolipoprotein diacylglyceryl transferase (Lgt), which converts them to prolipoproteins by adding a diacylglyceryl group to the sulfhydryl side chain of the invariant Cys₊₁ residue. Lipoprotein signal peptidase (LspA or signal peptidase II) subsequently cleaves the signal peptide, liberating the α-amino group of Cys₊₁, which can eventually be further modified. Here, we identified the <i>lgt</i> and <i>lspA</i> genes from <i>Corynebacterium glutamicum</i> and found that they are unique but not essential. We found that Lgt is necessary for the acylation and membrane anchoring of two model lipoproteins expressed in this species: MusE, a <i>C. glutamicum</i> maltose-binding lipoprotein, and LppX, a <i>Mycobacterium tuberculosis</i> lipoprotein. However, Lgt is not required for these proteins' signal peptide cleavage, or for LppX glycosylation. Taken together, these data show that in <i>C. glutamicum</i> the association of some lipoproteins with membranes through the covalent attachment of a lipid moiety is not essential for further post-translational modification.