CRYSTAL-STRUCTURE ANALYSIS AND REFINEMENT AT 2-CENTER-DOT-15 ANGSTROM RESOLUTION OF AMICYANIN, A TYPE-I BLUE COPPER PROTEIN, FROM THIOBACILLUS-VERSUTUS

The crystal structure of the type I blue copper protein amicyanin from Thiobacillus versutus has been determined by Patterson search techniques on the basis of the molecular model of amicyanin from Paracoccus denitrificans, and refined by energy-restrained least-squares methods. Amicyanin crystallizes in the trigonal space group P32 with unit cell dimensions of a=b=87·40 A ̊, c=38·20 A ̊. The asymmetric unit is composed of three independent molecules centred on the crystallographic 32 axes. The final R-value is 17·4% for 15,984 reflections to a resolution of 2·15 Å. The polypeptide fold in amicyanin is based on the β-sandwich structure commonly found in blue copper proteins. Nine β strands are folded into two twisted β-sheets that pack together with a filling of non-polar residues between them. The geometry of the copper site is similar to that of plastocyanin. There are four ligands, arranged approximately as a distorted tetrahedron, to the copper atom: His54, Cys93, His96 and Met99. One of the copper ligands, His96, is exposed to the surface and lies in the centre of a cluster of seven hydrophobic residues. © 1994.