title: Thermodynamics and mechanism of the deamidation of sodium-bound asparagine.
abstract: The deamidation of asparagine (Asn) residues is the most common type of spontaneous post-translational protein modification and plays a vital role in inflammation, protein transformation, apoptosis, aging, and a number of degenerative diseases. Here we present a full molecular description of asparagine deamidation in the Na(+)(Asn) complex by studying its collision-induced dissociation (CID) with Xe using a guided ion beam tandem mass spectrometer (GIBMS). Advanced methods for analysis of the energy-dependent CID cross section, considering both competing and sequential processes, provide the 0 K barrier for deamidation after accounting for unimolecular decay rates, internal energy of reactant ions, and multiple ion-neutral collisions. Relaxed potential energy surface scans performed at the B3LYP/6-31G(d) level identify the transition state (TS) and intermediate reaction species for Na(+)(Asn) deamidation, structures that are further optimized at the B3LYP/6-311+G(d,p) level. Single-point energies of the key optimized structures are calculated at MP2(full), B3LYP, and B3P86 levels using a 6-311+G(2d,2p) basis set. This coordinated application of both experimental work and quantum chemical calculations allows for a complete characterization of the elementary steps of this reaction and identification of the rate-limiting elementary step of Asn deamidation. The latter is measured to require 1.61 +/- 0.08 eV and involves formation of a cyclic succinic ring structure.
authors.affiliation: Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Heaton
authors.forename: P B
authors.initials: PB
authors.lastname: Armentrout
mesh_terms: D000577:Amides / Q000378:metabolism; D000641:Ammonia; D001216:Asparagine / Q000378:metabolism*; D001224:Aspartic Acid; D010455:Peptides; D011499:Protein Processing, Post-Translational; D012964:Sodium / Q000378:metabolism*; D013387:Succinic Anhydrides; D053719:Tandem Mass Spectrometry; D013816:Thermodynamics
chemical_list: D000577:Amides; D010455:Peptides; D013387:Succinic Anhydrides; D001224:Aspartic Acid; C031801:succinic anhydride; D001216:Asparagine; D000641:Ammonia; D012964:Sodium