Influence of Polyproline Backbone on the Relative Acidity of Terminal Aspartic Acid

Authors

Yadwinder Singh Mann, University of the PacificFollow
Jianhua Ren, University of the PacificFollow

Poster Number

14a

Lead Author Affiliation

Bioanalytical and physical chemistry

Lead Author Status

Doctoral Student

Second Author Affiliation

Chemistry

Second Author Status

Faculty

Introduction/Abstract

Influence of Polyproline Backbone on the Relative Acidity of Terminal Aspartic Acid

Purpose

The focus of our study is to understand the conformation of polyproline in gas phase through the measurement of gas phase acidity. For this purpose we investigate the isomeric dipeptides, tripeptides and tetrapeptides containing a polyproline backbone with aspartic acid at C or N terminus. The relative acidity of terminal aspartic acid would indicate the orientation of individual dipoles in the helix which would further give insight into the type of conformation.

Method

The bracketing experiments were performed using tandem quadrupole mass spectrometer. The computational studies were also performed to understand the experimental observation. The electronic enthalpies obtained after optimizing the structures at HF/3-21G* level and finally at the B3LYP/6-311+G(d,p) level, were used to calculate theoretical gas-phase deprotonation enthalpy.

Results

The preliminary data obtained from the bracketing experiments with a series of reference acids suggested that the aspartic acid at the C terminus is more acidic than the N terminus. The theoretical gas phase acidity for DP₂-NH₂ was calculated to be 331 Kcal/mol while for P₂D-NH₂, the value is 328 Kcal/mol. Similarly, the P₃D-NH₂ with the gas phase acidity 325 kcal/ mol was found to be more acidic than DP₃NH₂ analogue having gas phase acidity value 332 kcal/mole. The tetrapeptide P₄D-NH₂ also follows the trend and found to be more acidic than DP₄-NH₂.

Significance

The proteins are the building block of all organisms. The conformational study of protein would help us to understand the function of proteins. All enzymes are made up of proteins and the active sites of enzymes are buried deep inside in a solvent free environment. It is for this reason we have conducted out studies in gas phase in order to mimic the real environment of protein inside the body. From the present study we can conclude that the individual dipoles are oriented from C to N terminus and the polyproline having terminal aspartic acid adopt PPI helix conformation in gas phase.

Location

DeRosa University Center

Format

Poster Presentation

Poster Session

Afternoon 1pm-3pm