CATALYTIC DOMAIN OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 INTEGRASE - IDENTIFICATION OF A SOLUBLE MUTANT BY SYSTEMATIC REPLACEMENT OF HYDROPHOBIC RESIDUES

The integrase protein of human immunodeficiency virus type 1 is necess ary for the stable integration of the viral genome into host DNA, Inte grase catalyzes the 3' professing of the linear viral DNA and the subs equent DNA strand transfer reaction that inserts the viral DNA ends in to host DNA, Although full-length integrase is required for 3' process ing and DNA strand transfer activities in vitro, the central core doma in of integrase is sufficient to catalyze an apparent reversal of the DNA strand transfer reaction, termed disintegration, This catalytic co re domain, as well as the full-length integrase, has been refractory t o structural studies by x-ray crystallography or NMR because of its lo w solubility and propensity to aggregate, In an attempt to improve pro tein solubility, we used site-directed mutagenesis to replace hydropho bic residues within the core domain with either alanine or lysine. The single substitution of lysine for phenylalanine at position 185 resul ted in a core domain that was highly soluble, monodisperse in solution , and retained catalytic activity, This amino acid change has enabled the catalytic domain of integrase to be crystallized and the structure has been solved to 2,5-Angstrom resolution [Dyda, F., Hickman, A. B., Jenkins, T. M., Engelman, A., Craigie, R. and Davies, D. R. (1994) Sc ience 266, 1981-1986]. Systematic replacement of hydrophobic residues may be a useful strategy to improve the solubility of other proteins t o facilitate structural and biochemical studies.