Two-Angstrom crystal structure of oxidized Chromatium high potential iron protein.

摘要: Abstract The 85-residue structure of Chromatium high potential iron protein (HiPIP) has been determined by x-ray diffraction methods at 2.0 A resolution, and is currently undergoing crystallographic refinement. partially refined HiPIP reported here an R factor 0.24. Moreover, bond distances angles have constrained to their expected values, so that a model may be constructed from standard brass parts. Thus, it unusually well structure. Fe4S*4 cluster (Carter, C. W., Jr., Freer, S. T., Xuong, Ng. H., Alden, R. A., Kraut, J. (1971) Cold Spring Harbor Symp. Quant. Biol. 36, 381–385) covalently attached the Fe—S bonds cysteine residues 43, 46, 63, 77. Residues 1–42 fold up upon this binding segment. Most interface between these NH2- COOH-terminal segments consists packed nonpolar side chains. chain segment containing Cys 77 trapped inside where forms stretch antiparallel β sheet with 17–20 in NH2-terminal half chain. This unusual architecture probably accounts for relatively stability (Dus, K., DeKlerk, Sletten, Bartsch, G. (1967) Biochim. Biophys. Acta 140, 291–311). Tyr 19 abuts manner similar observed 2 28 Peptococcus aerogenes ferredoxin (Adman, E. Sieker, L. C., Jensen, H. (1973) Chem. 248, 3987–3996). polypeptide conformation described, almost its entirety, as sequence α helical or extended conformations hairpin turns. most secondary structures are surprisingly close detailed geometry those predicted lowest energy. More than 75% main hydrogen bonding sites bonded either within (47%) water (30%). Thus formed prior complete assembly entire Hairpin turns conspicuously associated protein-water interface: they contain large majority polar chains carbonyl oxygen amido nitrogen atoms bind disproportionately fraction "fixed" molecules. Sequence-structure correlations type proposed Robson Pain (Robson, B., Pain, Mol. 58, 237–259) Lewis et al. (Lewis, P. N., Momany, F. Scheraga, A. Proc. Nat. Acad. Sci. U. 68, 2293–2297) turn out quite accurate, serious discrepancy can rationalized convincingly terms requirements. These observations appear weigh heavily against theories folding which involve early, nonspecific micelle formation 237–259).