BIOPHYSICAL AND ENZYMATIC-PROPERTIES OF THE CATALYTIC DOMAIN OF HIV-1INTEGRASE

A deletion derivative of the integrase protein from human immunodefici ency virus type-1 (HIV-1) consisting of the central core domain (amino acids 50-212) has been characterized biophysically and biochemically. This deletion mutant is of particular interest for structural studies as it can carry out the disintegration reaction suggesting the presen ce of an active site and, under certain conditions, is more soluble th an full-length integrase. The circular dichroism and fluorescence of t he deletion mutant and the 288-residue full-length integrase were simi lar, indicating that the core residues maintain similar overall confor mations in both proteins. The deletion mutant is approximately 10% mor e alpha-helical than the full-length protein. Analytical centrifugatio n demonstrated that both proteins undergo monomer-dimer association al though the truncated protein showed slightly less tendency to dimerize ; the dissociation constants were 2.5 x 10(-5) M for the full-length p rotein and 8.0 x 10(-5) M for the truncated protein. The disintegratio n activity of both proteins was also compared. Although a higher conce ntration of the truncation mutant was required for optimal activity, t he mutant did not have altered pH or Mn2+ requirements relative to the full-length protein. The combined biophysical and enzymatic studies s uggest that this truncated form of HIV-1 integrase is likely to be use ful for structural studies.