title: The influence of protein structure on the products emerging from succinimide hydrolysis.
abstract: Proteins are vulnerable to spontaneous, covalent modifications that may result in alterations to structure and function. Asparagines are particularly labile, able to undergo deamidation through the formation of a succinimide intermediate to produce either aspartate or isoaspartate residues. Although aspartates cannot undergo deamidation they can form a succinimide and result in the same products. Isoaspartyls are the principal product of succinimide hydrolysis, accounting for 65-85% of the emerging residues. The variability in the ratio of products emerging from succinimide hydrolysis suggests the ability of protein structure to influence succinimide outcome. In the H15D histidine-containing protein (HPr), phosphorylation of the active site aspartate catalyzes the formation of a cyclic intermediate. Resolution of this species is exclusively to aspartate residues, suggestive of either a succinimide with restrained hydrolysis, or an isoimide, from which aspartyl residues are the only possible product. Deletion of the C-terminal residue of this protein does not influence the ability for phosphorylation or ring formation, but it does allow for isoaspartyl formation, verifying a succinimide as the cyclic intermediate in H15D HPr. Isoaspartyl formation in H15D Delta85 is rationalized to occur as a consequence of elimination of steric restrictions imposed by the C terminus on the main-chain carbonyl of the succinimide, the required point of nucleophilic attack of a water molecule for isoaspartyl formation. This is the first reported demonstration of the influence of protein structure on the products emerging from succinimide hydrolysis.
authors.affiliation: Department of Biochemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E5, Canada.
authors.forename: Lance
authors.initials: L
authors.lastname: Athmer
authors.forename: Jason
authors.initials: J
authors.lastname: Kindrachuk
authors.forename: Fawzy
authors.initials: F
authors.lastname: Georges
authors.forename: Scott
authors.initials: S
authors.lastname: Napper
mesh_terms: D001224:Aspartic Acid / Q000378:metabolism*; D006868:Hydrolysis; D026581:Isoaspartic Acid / Q000378:metabolism; D010766:Phosphorylation; D011506:Proteins / Q000737:chemistry*; D013388:Succinimides / Q000378:metabolism*
chemical_list: D026581:Isoaspartic Acid; D011506:Proteins; D013388:Succinimides; C032620:succinimide; D001224:Aspartic Acid