Regulation of a viral proteinase by a peptide and DNA in one-dimensional space. I. binding to DNA and to hexon of the precursor to protein VI, pVI, of human adenovirus

Abstract

The precursor to adenovirus protein VI, pVI, is a multifunctional protein with different roles early and late in virus infection. Here we focus on two roles late in infection, binding of pVI to DNA and to the major capsid protein hexon. pVI bound to DNA as a monomer independent of DNA sequence with an apparent equilibrium dissociation constant, K(d(app.)), of 46 nM. Bound to double-stranded DNA, one molecule of pVI occluded 8 base pairs. Upon the binding of pVI to DNA, 3 sodium ions were displaced from the DNA. A ΔG of -4.54 kcal/mol for the nonelectrostatic free energy of binding indicated that a substantial component of the binding free energy resulted from nonspecific interactions between pVI and DNA. The proteolytically processed, mature form of pVI, protein VI, also bound to DNA; its K(d(app.)) was much higher, 307 nM. The binding assays were performed in 1 mM MgCl(2), because in the absence of magnesium, the binding to pVI or protein VI to DNA was too tight to determine a K(d(app.)). Three molecules of pVI bound to one molecule of the hexon trimer with an equilibrium dissociation constant K(d(app.)) of 1.1nM.