title: Isopeptide ligation catalyzed by quintessential sortase A: mechanistic cues from cyclic and branched oligomers of indolicidin.
abstract: The housekeeping transpeptidase sortase A (SrtA) from Staphyloccocus aureus catalyzes the covalent anchoring of surface proteins to the cell wall by linking the threonyl carboxylate of the LPXTG recognition motif to the amino group of the pentaglycine cross-bridge of the peptidoglycan. SrtA-catalyzed ligation of an LPXTG containing polypeptide with an aminoglycine-terminated moiety occurs efficiently in vitro and has inspired the use of this enzyme as a synthetic tool in biological chemistry. Here we demonstrate the propensity of SrtA to catalyze "isopeptide" ligation. Using model peptide sequences, we show that SrtA can transfer LPXTG peptide substrates to the ε-amine of specific Lys residues and form cyclized and/or a gamut of branched oligomers. Our results provide insights about principles governing isopeptide ligation reactions catalyzed by SrtA and suggest that although cyclization is guided by distance relationship between Lys (ε-amine) and Thr (α-carboxyl) residues, facile branched oligomerization requires the presence of a stable and long-lived acyl-enzyme intermediate.
authors.affiliation: National Institute of Immunology, New Delhi 110 067, India.
authors.forename: Sayani
authors.initials: S
authors.lastname: Dasgupta
authors.forename: Sharmishtha
authors.initials: S
authors.lastname: Samantaray
authors.forename: Dinkar
authors.initials: D
authors.lastname: Sahal
authors.forename: Rajendra P
authors.initials: RP
authors.lastname: Roy
mesh_terms: D020816:Amino Acid Motifs; D019881:Aminoacyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002384:Catalysis; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013211:Staphylococcus aureus / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D023181:Antimicrobial Cationic Peptides; D001426:Bacterial Proteins; C073143:indolicidin; D019881:Aminoacyltransferases; C120542:sortase A; D003546:Cysteine Endopeptidases