Refinement of the three-dimensional structures of cytochrome c3 from Desulfovibrio vulgaris Hildenborough at 1.67 Å resolution and from Desulfovibrio desulfuricans ATCC 27774 at 1.6 Å resolution

Abstract

The three-dimensional X-ray structures of cytochrome c 3 from Desulfovibrio vulgaris Hildenborough and from Desulfovibrio desulfuricans ATCC 27774 were previously determined at 1.9 and 1.75 Å resolution, respectively. More recently, higher resolution data were collected (at 1.67 and 1.6 Å respectively) using synchrotron radiation. The refinement of the previously determined three-dimensional structures using the new data resulted in more accurate structural models, with no significant changes of the initial structures. In cytochrome c 3 from D. vulgaris Hildenborough, the R-factor was lowered from 19.6 to 15.3% using SHELXL-93, complemented with inspection and correction of the model relative to the electron density. This cytochrome crystallises in space group P6 1 with a=77.3, b=77.3, c=77.1 Å, Z=12. Cytochrome c 3 from D. desulfuricans ATCC 27774 crystallises in space group P6 122 with a=62.71, b=62.71, c=111.09 Å, Z=12. The R-factor was lowered from 17.8 to 16.6% using the same refinement procedure. In this cytochrome the 71–74 loop region was rearranged with no evidence of the previously found disorder, and disorder models were introduced in the terminal regions of residues serine 84 and lysine 90. The resulting higher-resolution structural models for both cytochromes are analyzed and compared with those previously obtained.