49] Modification of bacterial lipoproteins

Abstract

This chapter summarizes current knowledge of the lipid modification enzymes in the pathway for the maturation of bacterial lipoproteins. Lipid modification of bacterial lipoproteins is catalyzed by three enzymes: diacylglyceryltransferase, signal peptidase II, and N -acyltransferase. Major phospholipids in the bacterial cell envelope serve as both the diacylglyceryl and acyl donors. Phosphatidylglycerol (PG) is the major diacylglyceryl donor for diacylglyceryltransferase, whereas N -acyltransferase does not exhibit a preference for any particular acyl donor. The ability of Tricine- sodium dodecyl sulfate polyacrylamide gel (SDS-PAGE) to separate the various intermediates in the biosynthesis of murein lipoprotein is exploited to develop assays for diacylglyceryl modification of prolipoprotein and for N -acylation of apolipoprotein. A simpler and quicker peptide-based assay for diacylglyceryltransferase is available and a similar one for N -acyltransferase is required for its purification. The availability of the genes for the enzymes should enable hyper expression and the development of simple purification protocols. The specificity toward PG in vivo is demonstrated in vitro by delipidating the inverted vesicles with aqueous acetone extraction followed by incubation of the delipidated enzyme preparations with individual phospholipid species.