Thermodynamics and Mechanisms of Protonated Asparaginyl-Glycine Decomposition.
Deamidation at asparagine residues, a spontaneous post-translational modification in proteins, plays a significant role in various biological processes and degenerative diseases. In the current work, we present a full description of the deamidation process as well as other key fragmentations (dehydration, peptide bond cleavage, and loss of 2 NH3) from protonated asparaginyl-glycine, H(+)(AsnGly), by studying its kinetic energy dependent collision-induced dissociation (CID) with Xe using a guided ion beam tandem mass spectrometer. These results are compared with those for sustained off-resonance irradiation (SORI)-CID of H(+)(AsnGly) with Ar in a Fourier transform ion cyclotron resonance mass spectrometer. Computationally, simulating annealing methodology and a series of relaxed potential energy scans at the B3LYP/6-31G(d) level were performed to identify all intermediate and transition state (TS) structures for each key reaction. All species were further optimized at the B3LYP and B3LYP-GD3BJ/6-311+G(d,p) levels of theory. Single point energies of all major reaction species were calculated at the B3LYP, B3P86, MP2(full), and B3LYP-GD3BJ levels of theory and using M06-2X for rate-limiting species. Relative energies of intermediates, TSs, and products allow characterization of the elementary and rate limiting steps in H(+)(AsnGly) decomposition. By combining experimental and computational results, the complete mechanistic nature of H(+)(AsnGly) deamidation and other fragmentations is explored and compared to the previously studied H(+)(Asn) complex. The influence of water solvation on key TSs is also explored. On a fundamental level, this analysis will aid in understanding the thermodynamic and kinetic characteristics of the key intramolecular interactions involved in deamidation, dehydration, and other important fragmentations of peptides.
Department of Chemistry, University of Utah , 315 S. 1400 E. Rm. 2020, Salt Lake City, Utah 84112, United States.
Georgia C
GC
Boles
Department of Chemistry, Wayne State University , Detroit, Michigan 48202, United States.
R R
RR
Wu
Department of Chemistry, Wayne State University , Detroit, Michigan 48202, United States.
M T
MT
Rodgers
Department of Chemistry, University of Utah , 315 S. 1400 E. Rm. 2020, Salt Lake City, Utah 84112, United States.
P B
PB
Armentrout
D001216:Asparagine / Q000737:chemistry* / Q000378:metabolism; D004151:Dipeptides / Q000737:chemistry*; D005998:Glycine / Q000737:chemistry*; D008958:Models, Molecular; D011522:Protons; D053719:Tandem Mass Spectrometry; D013816:Thermodynamics; D014978:Xenon / Q000737:chemistry
D004151:Dipeptides; D011522:Protons; D014978:Xenon; D001216:Asparagine; D005998:Glycine