Identification of the Lyso-FormN-Acyl Intramolecular Transferase in Low-GC Firmicutes.
Bacterial lipoproteins are embedded in the cell membrane of both Gram-positive and Gram-negative bacteria, where they serve numerous functions central to cell envelope physiology. Lipoproteins are tethered to the membrane by anN-acyl-S-(mono/di)-acyl-glyceryl-cysteine anchor that is variously acylated depending on the genus. In several low-GC, Gram-positive firmicutes, a monoacyl-glyceryl-cysteine with an N-terminal fatty acid (known as the lyso form) has been reported, though how it is formed is unknown. Here, through an intergenic complementation rescue assay inEscherichia coli, we report the identification of a common orthologous transmembrane protein in bothEnterococcus faecalisandBacillus cereusthat is capable of forming lyso-form lipoproteins. When deleted from the native host, lipoproteins remain diacylated with a free N terminus, as maturation to theN-acylated lyso form is abolished. Evidence is presented suggesting that the previously unknown gene product functions through a novel intramolecular transacylation mechanism, transferring a fatty acid from the diacylglycerol moiety to the α-amino group of the lipidated cysteine. As such, the discovered gene has been namedlipoproteinintramoleculartransacylase (lit), to differentiate it from the gene for the intermolecularN-acyltransferase (lnt) involved in triacyl lipoprotein biosynthesis in Gram-negative organisms.IMPORTANCEThis study identifies a new enzyme, conserved among low-GC, Gram-positive bacteria, that is involved in bacterial lipoprotein biosynthesis and synthesizes lyso-form lipoproteins. Its discovery is an essential first step in determining the physiological role of N-terminal lipoprotein acylation in Gram-positive bacteria and how these modifications impact bacterial cell envelope function.
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA.
Krista M
KM
Armbruster
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA txm50@psu.edu.
Timothy C
TC
Meredith
D000215:Acylation; D000217:Acyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001409:Bacillus cereus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003545:Cysteine / Q000032:analysis / Q000378:metabolism; D013293:Enterococcus faecalis / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005227:Fatty Acids / Q000032:analysis / Q000378:metabolism; D008074:Lipoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D005227:Fatty Acids; D008074:Lipoproteins; D000217:Acyltransferases; D003545:Cysteine
acyl transferase; firmicutes; lipoproteins