The 1.5 angstrom crystal structure of a bleomycin resistance determinant from bleomycin-producing Streptomyces verticillus

Bleomycin (Bm)-binding protein, designated BLMA, which is a Bm resistance d eterminant from Bm-producing Streptomyces verticillus, was crystallized in a form suitable for X-ray diffraction analysis. The diffraction intensity d ata were collected up to a resolution of 1.5 Angstrom with a merging R-valu e of 0.054 at a completeness of 94%. The BLMA structure, determined by the single isomorphous replacement method including the anomalous scattering ef fect (SIR-AS) at a resolution of 2.0 Angstrom, was refined at 1.5 Angstrom resolution. The final R-factor was 19.0% and R-free was 22.1% including 91 water molecules. The crystal packing showed a dimer form, which was generat ed by arm exchange. The 1.5 Angstrom high-resolution experiment allowed an analysis of the side-chain disorder of BLMA. The structural comparison of B LMA with a homologous protein from Streptoalloteichus hindustanus, designat ed Shble protein, showed that a Ser100-Gly103 loop was farther from the gro ove, which is a Bm-binding site, in BLMA than in the Shble protein. Further more the hydrophobicity of the groove in BLMA is much lower than that in th e Shble protein. The structural differences between these proteins may be r esponsible for the observation that a half-saturating concentration (K-1/2) of Bm is higher for BLMA than for the Shble protein. (C) 2000 Academic Pre ss.