Poster abstracts

Poster number 4 submitted by Lana Bengez

Thermodynamic characterization of e. coli manganese superoxide dismutase binding to single- and double-stranded polynucleic acids

Lana Bengez (Chemistry, John Carroll University), Iteen Cheng (Chemistry, John Carroll University), Angela C. Smolik (Technology Transfer, Case Western Reserve University), David P. Mascotti (Chemistry, John Carroll University)

Abstract:
Bacterial manganese superoxide dismutase (MnSOD) has been shown to localize to the chromosomal portion of the cell and impart protection from ionizing radiation to DNA. The binding affinity of bacterial MnSOD to non-sequence specific double stranded oligomeric DNA has been quantitated previously by nitrocellulose filter binding and gel shift assays. We have examined the equilibrium binding of E. coli MnSOD containing tryptophan to poly(U), poly(A), poly(C), poly(dU) and double-stranded (ds) DNA. Equilibrium association constants, Kobs, measured by monitoring tryptophan fluorescence quenching, were examined as functions of monovalent salt (MX) concentration and type, as well as temperature, from which deltaG°obs and deltaH°obs were determined. The polynucleotides bind to MnSOD in the following affinity hierarchy, poly(dU)>poly(U)>dsDNA>poly(A)>poly(C). For each polynucleotide, Kobs decreases with increasing [K+]. For polyU, polyA and polyC the values of deltaHobs become less favorable with increasing [K+]; therefore, the salt concentration dependence of deltaG°obs has contributions from entropic and enthalpic origins such that dlogKobs/dlog[K+] is less negative than if it were a simple electrostatic binding event.

Keywords: MnSOD, protein-RNA interactions, thermodynamics