Regulation of a Viral Proteinase by a Peptide and DNA in One-dimensional Space

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, Kd(app), of 46 nm. Bound to double-stranded DNA, one molecule of pVI occluded 8 bp. Upon the binding of pVI to DNA, three sodium ions were displaced from the DNA. A ΔG00 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 Kd(app) was much higher, 307 nm. The binding assays were performed in 1 mm MgCl2 because in the absence of magnesium, the binding to pVI or protein VI to DNA was too tight to determine a Kd(app). Three molecules of pVI bound to one molecule of the hexon trimer with an equilibrium dissociation constant Kd(app) of 1.1 nm. Background: The C terminus of pVI activates the adenovirus proteinase. pVI escorts hexon into the nucleus. Results: pVI binds tightly to DNA independent of sequence, Kd = 46 nm. pVI binds tightly to hexon, Kd = 1.1 nm. Conclusion: DNA binding of pVI is the first step in the activation of adenovirus proteinase. Significance: This step links pVI, hexon, viral DNA, and the adenovirus proteinase in virion maturation.