Biomedical subjects

Mateo Obregón

Publications and source records attributed to Mateo Obregón.

4 recordsLinked to original sources

PubMed2006

Wave function analysis of MHC-peptide interactions.

We have carried out an analysis of the wave function data for three MHC-peptide complexes: HLA-DRbeta1*0101-HA, HLA-DRbeta1*0401-HA and HLA-DRbeta1*0401-Col. We used quantum chemistry computer programs to generate wave function coefficients for these complexes, from which we obtained both molecular and atomic orbital data for both pocket and peptide amino acids within each pocket region. From these discriminated data, interaction molecular orbitals (IMOs) were identified as those with large and similar atomic orbital coefficient contributions from both pocket and peptide amino acids. The present results correlate well with our previous research where only electrostatic moments were used to explore molecular component interactions. Furthermore, we show a quantum chemical methodology to produce more fine-grained results concerning amino acid behavior in the MHC-peptide interaction.

Amino Acids↗

PubMed2005

A comparative study of MHC Class-II HLA-DRbeta10401-Col II and HLA-DRbeta10101-HA complexes: a theoretical point of view.

A study was performed on the HLA-DRbeta1*0401-collagen II peptide complex using the computation of electronic multipolar variables proposed by us previously. Furthermore, these results were compared with those obtained for the HLA-DRbeta1*0101-haemaglutinin peptide complex studied by us with the same tools, confirming that Pocket 1 for this new complex is also the most important pocket for the interaction between the presenting molecule and the presented peptide. The pocket hierarchy established for HLA-DRbeta1*0401 allele was P1 >> P9 approximately P7 > P6 > P4, whilst a P1 >> P4 > P9 approximately P7>P6 pocket hierarchy was found for HLA-DRbeta1*0101, showing how the relative importance of the pockets distinguishes the two alleles. There are high correlation levels with experimental results (when possible), again confirming the validity of using calculated values for electronic multipolar variables as a useful tool for studying interactions between immune system molecules and peptides.

Antigen Presentation↗

PubMed2004

Quantum chemical analysis explains hemagglutinin peptide-MHC Class II molecule HLA-DRbeta1*0101 interactions.

We present a new method to explore interactions between peptides and major histocompatibility complex (MHC) molecules using the resultant vector of the three principal multipole terms of the electrostatic field expansion. Being that molecular interactions are driven by electrostatic interactions, we applied quantum chemistry methods to better understand variations in the electrostatic field of the MHC Class II HLA-DRbeta1*0101-HA complex. Multipole terms were studied, finding strong alterations of the field in Pocket 1 of this MHC molecule, and weak variations in other pockets, with Pocket 1>>Pocket 4>Pocket 9 approximately Pocket 7>Pocket 6. Variations produced by "ideal" amino acids and by other occupying amino acids were compared. Two types of interactions were found in all pockets: a strong unspecific one (global interaction) and a weak specific interaction (differential interaction). Interactions in Pocket 1, the dominant pocket for this allele, are driven mainly by the quadrupole term, confirming the idea that aromatic rings are important in these interactions. Multipolar analysis is in agreement with experimental results, suggesting quantum chemistry methods as an adequate methodology to understand these interactions.

Binding Sites↗

PubMed2002

Constructing a useful tool for characterizing amino acid conformers by means of quantum chemical and graph theory indices.

The aim of this work is to construct a tool to assist in the prediction of peptidic properties resulting from the exchange of two amino acids in a proteic chain. In the past others have used experimental properties for this purpose. However, the nature of these data sets severely limits their access to important properties pertaining to secondary structure, and hence the indices used cannot characterize different backbone conformers like alpha helix and beta strands, or side-chain conformations like gauche +, gauche - and trans. In this study we explore the importance of backbone and side-chain angles with regard to conformer similarity measured with theoretical properties calculated in an ab initio manner. For each of the 20 genetically encoded amino acids, we studied five conformers that correspond to alpha helical and beta strand structures, with three different side chain conformations for each, defined solely by their angles phi, psi and chi1. This methodology allowed each of the 108 conformers to be represented by a mathematical object without ambiguity. The peptidic chain was emulated using two capping models to simulate the effect of nearest neighbors. These are OHC-Xaa-NH2 and Ala-Xaa-Ala, where Xaa is the conformer of interest. We then calculated 40 ab initio quantum chemical and graph theory indices for each backbone-side-chain conformer to obtain a characterization and classification scheme. We found that: (1) while backbone structure is very important to conformer similarity, side-chain conformations do not cluster together in a top-level manner; (2) amino acids with pi electrons group together independent of backbone conformation.