STRUCTURE AT 2.7 ANGSTROM RESOLUTION OF THE PARACOCCUS-DENITRIFICANS 2-SUBUNIT CYTOCHROME-C-OXIDASE COMPLEXED WITH AN ANTIBODY F-V FRAGMENT

The aa(3) type cytochrome c oxidase consisting of the core subunits I and II only was isolated from the soil bacterium Paracoccus denitrific ans and crystallized as complex with a monoclonal antibody F-v fragmen t, Crystals could be grown in the presence of a number of different no nionic detergents, However, only undecyl-beta-D-maltoside and cyclehex yl-hexyl-beta-D-maltoside yielded well-ordered crystals suitable for h igh resolution x-ray crystallographic studies, The crystals belong to space group P2(1)2(1)2(1) and diffract x-rays to at least 2.5 Angstrom (1 Angstrom = 0.1 nm) resolution using synchrotron radiation, The str ucture was determined to a resolution of 2.7 Angstrom using molecular replacement and refined to a crystallographic R-factor of 20.5% (R-fre e = 25.9%), The refined model includes subunits I and II and the 2 cha ins of the F-v fragment, 2 heme A molecules, 3 copper atoms, and 1 Mg/ Mn atom, a new metal (Ca) binding site, 52 tentatively identified wate r molecules, and 9 detergent molecules, Only four of the mater molecul es are located in the cytoplasmic half of cytochrome c oxidase. Most o f them are near the interface of subunits I and II, Several waters for m a hydrogen-bonded cluster, including the heme propionates and the Mg /Mn binding site, The F-v fragment binds to the periplasmic polar doma in of subunit II and is critically involved in the formation of the cr ystal lattice, The crystallization procedure is well reproducible and will allow for the analysis of the structures of mechanistically inter esting mutant cytochrome c oxidases.