Poster abstracts

Poster number 22 submitted by Nicholas Callahan

Transition between Adenylate kinase structures

Nicholas Callahan (OSU Biophysics Program), Deepa Perera (Muskingum University Dept. of Chemistry), Jendy Weppler (Muskingum University Dept. of Chemistry), Will Ray (Battelle Center of Mathematical Medicine), Thomas Magliery (OSU Dept. of Chemistry)

Abstract:
In the course of protein evolution, the interactions between side-chains are optimized for overall organism fitness. An enzyme must both be stable and fulfill its metabolic role within certain kinetic parameters. Because the preferred environment of organisms can vary widely across phylogenies,homologous enzymes can have similar backbones but different side chain packing, thereby fine-tuning interaction strength and dynamic mechanisms for environmental conditions. This evolution-driven varying of side chain packing can create positional correlations in multiple sequence alignments. It has been shown that these correlations may reflect stabilizing interactions, but do not necessarily do so. We present here correlation-guided mutations made in the adenylate kinase enzyme of Bacillus subtilis bacteria (bsADK) which, in the context of a destabilized variant, affect kinetic activity without altering stability. The folded lid domain of bacterial ADK closes over the active site following substrate binding. This domain is stabilized by either a zinc-chelating motif in gram-positive species or by a network of hydrogen bonds in gram-negative species. Mutating the four chelating residues of bsADK to their counterparts in E. coli ADK (ecADK), abolishing metal-binding, results in a severe drop in global stability and the loss of enzymatic activity. Using mutual information analysis, we located two positions in the lid domain strongly correlated to chelating motif. Further mutations were made in bsADK at these positions. These additional mutations were found to have little effect on global stability, but served to partially rescue enzymatic activity. Although it is understood that loss and gain of stability can directly alter the dynamics of adenylate kinase, the fact that these variants do not vary in stability suggests that they could serve as an experimental system for further studying the kinetic pathway of this enzyme. We are currently pursuing biophysical strategies to further characterize these variants and elaborate on their kinetic differences.

Keywords: Evolution, Enzyme, Sequence Alignment