title: Aspartate Glycosylation Triggers Isomerization to Isoaspartate.
abstract: O-Linked β-N-acetylglucosamine transferase (OGT) is an essential human enzyme that glycosylates numerous nuclear and cytoplasmic proteins on serine and threonine. It also cleaves Host cell factor 1 (HCF-1) by a mechanism in which the first step involves glycosylation on glutamate. Replacing glutamate with aspartate in an HCF-1 proteolytic repeat was shown to prevent peptide backbone cleavage, but whether aspartate glycosylation occurred was not examined. We report here that OGT glycosylates aspartate much faster than it glycosylates glutamate in an otherwise identical model peptide substrate; moreover, once formed, the glycosyl aspartate reacts further to form a succinimide intermediate that hydrolyzes to produce the corresponding isoaspartyl peptide. Aspartate-to-isoaspartate isomerization in proteins occurs in cells but was previously thought to be exclusively non-enzymatic. Our findings suggest it may also be enzyme-catalyzed. In addition to OGT, enzymes that may catalyze aspartate to isoaspartate isomerization include PARPs, enzymes known to ribosylate aspartate residues in the process of poly(ADP-ribosyl)ation.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University , Cambridge, Massachusetts 02138, United States.|Department of Microbiology and Immunobiology, Harvard Medical School , Boston, Massachusetts 02115, United States.
authors.forename: John
authors.identifier: 0000-0003-1604-2515
authors.initials: J
authors.lastname: Janetzko
authors.affiliation: Department of Microbiology and Immunobiology, Harvard Medical School , Boston, Massachusetts 02115, United States.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Walker
mesh_terms: D001224:Aspartic Acid / Q000096:biosynthesis* / Q000737:chemistry; D055162:Biocatalysis; D006031:Glycosylation; D051863:Host Cell Factor C1 / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008968:Molecular Conformation; D017351:N-Acetylglucosaminyltransferases / Q000378:metabolism*
chemical_list: C497692:HCFC1 protein, human; D051863:Host Cell Factor C1; D001224:Aspartic Acid; D017351:N-Acetylglucosaminyltransferases