THE CRYSTAL-STRUCTURE OF THE CATALYTIC DOMAIN OF THE SITE-SPECIFIC RECOMBINATION ENZYME GAMMA-DELTA RESOLVASE AT 2.7-A RESOLUTION

The crystal structure of the catalytic domain of the site-specific recombination enzyme gamma-delta resolvase has been determined at 2.7 angstrom resolution. Its first 120 amino acids form a central five-stranded, beta-pleated sheet surrounded by five alpha-helices. In one of the four dyad-related dimers, the two active site Ser-10 residues are 19 angstrom apart, perhaps close enough to contact and become covalently linked to the DNA at the recombination site. This dimer also forms the only closely packed tetramer found in the crystal. The subunit interface at a second dyad-related dimer is more extensive and more highly conserved among the homologous recombinases; however, its active site Ser-10 residues are more than 30 angstrom apart. Side chains, identified by mutations that eliminate catalysis but not DNA binding, are located on the subunit surface near the active site serine and at the interface between a third dyad-related pair of subunits of the tetramer.