Protein structure is directly related to protein function, and the amino acid sequence that represents a particular gene contains all the necessary information to achieve that structure. I am interested in how protein structures evolve, with particular emphasis on utilization of the iron-protoporphyrin cofactors such as heme from hemoglobin and myoglobin. My studies of heme-proteins can be divided into two major projects.
1. Biophysical characterization of a heme-peptide construct from cytochrome c: This project involves the examination of the factors that modulate reduction potential in cytochrome c, and important protein in the electron transport chain. Cytochrome c is characterized by a c-type heme, where the heme is covalently attached to the protein through two vinyl groups and two conserved cysteine residues in a CXXCH motif. The XX in the motif represents that nearly any combination of amino acids have been found in different genes. In particular, this protect is concerned with the role of the variable XX residues in promoting heme distortion through steric strain on the covalently attached cysteines. The project will involve studying a heme-peptide construct that represents the CXXCH attachment motif. Site directed mutagenesis will be used to examine the effect of residue size in the XX region. Subsequent biophysical characterization will be done with NMR, cyclic voltammetry, and UV-Vis spectroscopy to look at heme electronic structure and reduction potential.
2. A phylogenetic and structural analysis 2/2 hemoglobins
Phylogenetics is a field of bioinformatics concerned with establishing evolutionary relationships between species by examining changes in gene sequences. My particular interest in phylogenetics involves its use to establish the structurally relevant (and therefore functionally relevant) areas of proteins. In particular, I study the phylogenetic relationships within a protein family that is part of the hemoglobin superfamily called 2/2 globins (or truncated globins). The globin region of these proteins is shorter than that in hemoglobin and myoglobin by 20-30 residues and achieves a 2/2 helical fold as opposed to the typical 3/3 fold. Most of the sequences in this family are of bacterial origin and have an unknown function. As more sequences and three-dimensional structures become available, continued phylogenetic analysis is necessary to understand the complex relationships in this protein family. The project includes using Blast searches find homologous sequences, establishing orthologs, doing sequence alignments, and examining protein structures.
Scott NL, Xu Y, Shen G, Vuletich DA, Falzone CJ, Li Z, Ludwig M, Pond MP, Preimesberger MR, Bryant DA, Lecomte JT. Functional and Structural Characterization of the 2/2 Hemoglobin from Synechococcus sp. PCC 7002 . Biochemistry. 2010 Aug 24;49(33):7000-11.
Vuletich, D.A. and Lecomte, J.T.J. (2008) The Phylogeny and structural properties of 2/2 hemoglobins. In Protein Reviews: Dioxygen Binding and Sensing Proteins. Atassi, M.Z. Ed. 9:31–43.
Vuletich DA, Falzone CJ, Lecomte JT. Structural and dynamic repercussions of heme binding and heme-protein cross-linking in Synechococcus sp. PCC 7002 hemoglobin. Biochemistry. 2006 Nov 28;45(47):14075-84.
Vuletich DA, Lecomte JT. A phylogenetic and structural analysis of truncated hemoglobins. J Mol Evol. 2006 Feb;62(2):196-210. Epub 2006 Feb 10.
Lecomte JT, Vuletich DA, Lesk AM. Structural divergence and distant relationships in proteins: evolution of the globins. Curr Opin in Struct Biol. 2005 Jun; 15(3): 290-301.