The variation of the gas phase acidity of a cysteine residue in oligopeptides

<p>The altered acidities of amino acid residues in folded proteins can be used as a good indication for the diverse functions, stabilities as well as folding-unfolding states of the proteins. Previously, our group has investigated the gas phase acidities of a series of cysteine containing peptides of four residues and longer. The results showed that the helix macrodipole might have a significant influence on the acidities of these peptides. In this work, the gas phase acidities of isomeric small cysteine containing di- and tri-peptides were investigated experimentally and computationally.</p><p> The gas phase acidities (Δ_acidG) and related thermochemical quantities (Δ_acidH and Δ_acidS) were determined by using the extended Cooks kinetic method. A triple-quadruple mass spectrometer interfaced with an electrospray ionization source was employed for the study. The gas phase acidities of the N-terminal cysteine peptides (CysAla_1,2NH₂ and CysGly_1,2NH₂) were determined to be in the range of 321-323 kcal/mol, and the acidities of the C-terminal cysteine peptides (Ala_1,2CysNH₂ and Gly_1,2CysNH₂) were around 327- 331 kcal/mol. The results showed that theN-cysteine peptides were more acidic than the corresponding C-cysteine peptides, tri-peptides were stronger acids than di-peptides, and the acidities of cysteine-polyglycine peptides were close to those of the cysteine-polyalanine analogues.</p><p>Computational studies were performed through conformer search, geometry optimization, and energy calculations using the Spartan and the Gaussian suite of programs. The results showed that the low energy conformations of all deprotonated peptides were coils. The greater acidities of the N-cysteine peptides were likely due to the stronger hydrogen-bonding interactions in the deprotonated N-cysteine peptides, which efficiently stabilized the thiolate anions. The theoretically predicted acidities were in good agreements with the experimental results.</p>

Name thesis:degree_name

Master of Science (M.S.)

Level thesis:degree_level

Thesis - Pacific Access Restricted

Discipline thesis:degree_discipline

Chemistry

Year dc:date.available

2011

Author dc:creator

• Shen, Jialin

Contributors dc:contributor

• Jianhua Ren

• Acid-base chemistry
• Oligopeptides
• Physical Sciences and Mathematics

Licence

• http://rightsstatements.org/vocab/InC/1.0/

Repository record dc:identifier

https://scholarlycommons.pacific.edu/uop_etds/791

OAI identifier oai:identifier

oai:scholarlycommons.pacific.edu:uop_etds-1790