Evidence to Suggest Bacterial Lipoprotein Diacylglyceryl Transferase (Lgt) is a Weakly Associated Inner Membrane Protein.

Abstract

The unique and ubiquitous bacterial lipoprotein biosynthesis pathway is an attractive new antibiotic target. Crystal structures of its three biosynthetic enzymes have been solved recently. The first enzyme, Phosphatidylglycerol:proLipoprotein diacylglyceryl Transferase (Lgt), which initiates the post-translational modification at the metabolic interface of protein biosynthesis, phospholipid biosynthesis, protein secretion and lipid modification was reported to be a seven-transmembrane helical structure with a catalytic periplasmic head. Its complete solubilization in water or mild detergent in a fully active state, its chromatographic behaviour as an active monomer in the absence of detergent and recovery of active whole-length protein after proteolytic treatment of spheroplasts cast serious doubts about its proposed membrane association and orientation. Rather, it could be a seven-helical bundle partially embedded in the inner membrane's inner leaflet aided by hydrophobic interaction. In fact, there are examples where originally reported seven-transmembrane proteins were later shown to be seven-helical peripheral membrane proteins based on solubilization criterion and re-analysis. Validated computational tool, Membrane Optimal Docking Area (MODA), also predicted a weaker association of Lgt's helices with the membrane compared to typical transmembrane proteins. This insight is crucial to Lgt-based antibiotic design.