Two-Angstrom crystal structure of oxidized Chromatium high potential iron protein.
Two-Angstrom crystal structure of oxidized Chromatium high potential iron protein.
复制标题
氧化铬高电位铁蛋白的两埃晶体结构。
DOI：
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发表时间：
1976
影响因子：
4.8
通讯作者：
R. G. Bartsch
中科院分区：
文献类型：
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作者：
C. Carter;J. Kraut;S. Freer;Nguyen;R. A. Alden;R. G. Bartsch
摘要用X射线衍射方法在2.0 A分辨率下测定了Chromatium高电位铁蛋白（HiPIP）的85个残基结构，目前正在进行晶体学精修。本文报道的部分精制的HiPIP结构具有0.24的R因子。此外，键合距离和角度已被约束到其预期值，以便可以从标准黄铜零件构建模型。因此，它是一种异常明确的蛋白质结构。Fe_4S ~（*4）团簇（Carter，C. W.，小的，Freer，S. T.，Xuong，Ng. H、奥尔登河一、和Kraut，J.（1971）冷泉港研讨会。定量36，381-385）通过Fe-S键在半胱氨酸残基43、46、63和77处共价连接至蛋白质。残基1-42在该簇结合区段上折叠。这些NH 2-和COOH-末端片段之间的大多数界面由包装的非极性侧链组成。含有Cys 77的链段被捕获在该界面内，在该界面处，它与链的NH 2-末端一半中的残基17-20形成一段反平行β折叠。这种不寻常的架构可能解释了HiPIP相对高的稳定性（Dus，K.，DeKlerk，H.，Sletten，K.，和Bartsch，R. G.（1967）Biochim. Biophys. Acta 140，291-311）。Tyr 19侧链以类似于对产气消化球菌铁氧还蛋白中的Tyr 2和Tyr 28观察到的方式邻接Fe 4S *4簇（Adman，E. T.，锡克湖C.的方法，和詹森，L. H.（1973）J.Biol.Chem.248，3987-3996）。多肽链的构象几乎全部可以描述为α螺旋或延伸构象和发夹转角的序列。此外，这些二级结构中的大多数在它们的详细几何结构中令人惊讶地接近于预测的最低能量。超过75%的主链氢键位点在二级结构内（47%）或与水（30%）键合。因此，这些结合可以在整个结构的完全组装之前形成。发夹弯与蛋白质-水界面显著相关：它们含有绝大多数极性侧链，并且它们的主链羰基氧和酰胺基氮原子结合不成比例的大部分“固定”水分子。Robson和Pain提出的序列-结构相关性类型（Robson，B.，Pain，R. H.等（1971）J. Mol. 58，237-259）和刘易斯等人（刘易斯，P.N.，Momany，F.一、和Scheraga，H. A.等人（1971）Proc. Sci.联合S. A. 68，2293-2297）被证明是相当准确的，并且预测和观察到的结构之间最严重的差异可以令人信服地合理化在Fe 4S *4簇结合要求方面。这些观察结果似乎与蛋白质折叠的理论有很大的矛盾，蛋白质折叠涉及早期的非特异性胶束形成（Robson，B.，Pain，R. H.等（1971）J. Mol. 58，237-259）。
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. The partially refined HiPIP structure reported here has an R factor of 0.24. Moreover, bond distances and angles have been constrained to their expected values, so that a model may be constructed from standard brass parts. Thus, it is an unusually well determined protein structure. The Fe4S*4 cluster (Carter, C. W., Jr., Freer, S. T., Xuong, Ng. H., Alden, R. A., and Kraut, J. (1971) Cold Spring Harbor Symp. Quant. Biol. 36, 381–385) is covalently attached to the protein by Fe—S bonds at cysteine residues 43, 46, 63, and 77. Residues 1–42 fold up upon this cluster binding segment. Most of the interface between these NH2- and COOH-terminal segments consists of packed nonpolar side chains. The chain segment containing Cys 77 is trapped inside this interface where it forms a stretch of antiparallel β sheet with residues 17–20 in the NH2-terminal half of the chain. This unusual architecture probably accounts for the relatively high stability of HiPIP (Dus, K., DeKlerk, H., Sletten, K., and Bartsch, R. G. (1967) Biochim. Biophys. Acta 140, 291–311). The Tyr 19 side chain abuts the Fe4S*4 cluster in a manner similar to that observed for Tyr 2 and Tyr 28 in Peptococcus aerogenes ferredoxin (Adman, E. T., Sieker, L. C., and Jensen, L. H. (1973) J. Biol. Chem. 248, 3987–3996). The polypeptide chain conformation may be described, almost in its entirety, as a sequence of α helical or extended conformations and hairpin turns. Moreover, most of these secondary structures are surprisingly close in their detailed geometry to those predicted to be of lowest energy. More than 75% of the main chain hydrogen bonding sites are bonded either within secondary structures (47%) or to water (30%). Thus these bonds may be formed prior to complete assembly of the entire structure. Hairpin turns are conspicuously associated with the protein-water interface: they contain a large majority of the polar side chains and their main chain carbonyl oxygen and amido nitrogen atoms bind a disproportionately large fraction of the "fixed" water molecules. Sequence-structure correlations of the type proposed by Robson and Pain (Robson, B., and Pain, R. H. (1971) J. Mol. Biol. 58, 237–259) and Lewis et al. (Lewis, P. N., Momany, F. A., and Scheraga, H. A. (1971) Proc. Nat. Acad. Sci. U. S. A. 68, 2293–2297) turn out to be quite accurate, and the most serious discrepancy between predicted and observed structures can be rationalized convincingly in terms of Fe4S*4 cluster binding requirements. These observations appear to weigh heavily against theories of protein folding which involve early, nonspecific micelle formation (Robson, B., and Pain, R. H. (1971) J. Mol. Biol. 58, 237–259).