Crystal structure of oxidized Bacillus pasteurii cytochrome c553 at 0.97-A resolution.

This article reports the first X-ray structure of the soluble form of a c-type cytochrome isolated from a Gram-positive bacterium. Bacillus pasteurii cytochrome c553, characterized by a low reduction potential and by a low sequence homology with cytochromes from Gram-negative bacteria or eukaryotes, is a useful case study for understanding the structure−function relationships for this class of electron-transfer proteins. Diffraction data on a single crystal of cytochrome c553 were obtained using synchrotron radiation at 100 K. The structure was determined at 0.97-A resolution using ab initio phasing and independently at 1.70 A in an MAD experiment. In both experiments, the structure solution exploited the presence of a single Fe atom as anomalous scatterer in the protein. For the 0.97-A data, the phasing was based on a single data set. This is the most precise structure of a heme protein to date. The crystallized cytochrome c553 contains only 71 of the 92 residues expected from the intact protein sequence...