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Prokaryotic membrane lipoprotein lipid attachment site In prokaryotes, membrane lipoproteins are synthesized with a precursor signal peptide, which is cleaved by a specific lipoprotein signal peptidase (signal peptidase II). The peptidase recognizes a conserved sequence and cuts upstream of a cysteine residue to which a glyceride-fatty acid lipid is attached. Analysis of lipoprotein and non-lipoprotein signal peptides reveals that the two classes differ significantly only in the region close to the signal peptidase cleavage site. This region is apolar and has the consensus sequence LA(G,A) 1C in the lipoproteins, but is polar and has small, uncharged residues in positions - 3 and - 1 in the non-lipoproteins. Specialised signal peptide containing a lipobox motif in the carboxyl region of the signal peptide carries a cysteine residue which is the invariable target for lipidation by lipoprotein diacylglyceryl transferase (Lgt). Lipidation at this residue serves to anchor the lipoprotein to the membrane. Lipidation has been considered to be a prerequisite for the action of lipoprotein signal peptidase (Lsp), which removes the signal peptide and leaves the cysteine of the lipobox as the new amino-terminal residue of the mature lipoprotein. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",