Solution 1H NMR study of the heme cavity and folding topology of the abbreviated chain 118-residue globin from the cyanobacterium Nostoc commune.
Solution 1H NMR study of the heme cavity and folding topology of the abbreviated chain 118-residue globin from the cyanobacterium Nostoc commune.
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溶液 1H NMR 研究来自蓝藻发菜公社的短链 118 残基球蛋白的血红素腔和折叠拓扑。
DOI：
10.1021/bi992081l
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发表时间：
2000
期刊：
影响因子：
2.9
通讯作者：
LaMar,GN
中科院分区：
文献类型：
--
作者：
Yeh,DC;Thorsteinsson,MV;Bevan,DR;Potts,M;LaMar,GN
蓝藻发菜中的珠蛋白，缩写为GlbN，似乎是末端氧化酶的一部分，而不是作为呼吸色素，显示出相对正常的氧结合特性，尽管相对于更传统的珠蛋白[Thorsteinsson，M.V.，Bevan，D.R.，Potts，M.，Dou，Y.，Eich，R.F.，Hargrove，M.S.，Gibson，Q.H.，和Olson，J.S.(1999)BioChemical y38,2117−2126]，它显示出相对正常的氧结合特性。用1H核磁共振溶液研究了血红素空腔的性质和这种氰化血红蛋白的一般折叠拓扑结构，以确定这种致密的珠蛋白与标准的珠蛋白折叠的程度和方式。这是迄今为止进行结构分析的最小的球蛋白。之所以选择顺磁性的杂环化合物，是因为它特有的大的磁各向异性赋予了显着的偶极位移，这既提高了分辨率，极大地方便了指认，也作为珠蛋白折叠拓扑的指示剂。轴向His 70和高度保守的Phe 35(CD1)决定了血红素和近端His的绝对取向。四个螺旋片段和一个环片段的顺序分配证实了保存良好的F、G和H螺旋以及FG角的存在，这些片段表现出与血红素的偶极接触。相对于更传统长度的珠蛋白，链的大部分缩写被容纳在A−D螺旋中，其中最后一个完全缺失。为结合配体提供氢键的末端残基被鉴定为Gln 43，但预期的螺旋位置E7无法确定。His 46被放置在E10位置，根据质子化状态的不同，它在进入和离开血红素空腔时会采取不同的取向，这表明在低pH下存在玻尔效应。结果表明，主链质子对指定残基的偶极移位与其他花环球蛋白的观察到的偶极移位很好地吻合，并进一步支持保守的Mb折叠。受扰的中程偶极接触和F螺旋的与pH无关的主干质子不稳定性被解释为一种比传统长度的珠蛋白更不稳定的全蛋白。
The globin from the cyanobacteriumNostoc commune, abbreviated GlbN, which appears to serve as a part of a terminal oxidase rather than as a respiratory pigment, displays relatively normal O2binding properties, despite the highly abbreviated polypeptide chain, (118 residues) relative to more conventional globins [Thorsteinsson, M. V., Bevan, D. R., Potts, M., Dou, Y., Eich, R. F., Hargrove, M. S., Gibson, Q. H., and Olson, J. S. (1999)Biochemistry38, 2117−2126]. The nature of the heme cavity and the general folding topology of this cyanoglobin were investigated by solution1H NMR to establish the extent to which, and the manner in which, this compact globin adheres to the standard globin fold. This represents by far the smallest globin subjected to structural analysis. The paramagnetic cyanomet derivative was selected because its characteristically large magnetic anisotropy imparts significant dipolar shifts which both improve resolution to greatly facilitate assignments and serve as indicators of the folding topology of the globin. Identification of the axial His 70 and highly conserved Phe 35 (CD1) determined the absolute orientation of the heme and proximal His. Sequential assignments of four helical and one loop segments, which exhibit dipolar contacts to the heme and among each other, confirm the presence of well-conserved F, G, and H helices and the FG corner. The majority of the abbreviation of the chain relative to the more conventional length globins is accommodated in the A−D helices, of which the last is completely missing. The distal residue which provides a H-bond to bound ligand is identified as Gln 43, but the expected helical position E7 could not be confirmed. His 46, placed at position E10, is found to adopt alternate orientations into, and out of, the heme cavity depending on protonation state, suggesting the presence of a Bohr effect at low pH. It is shown that the dipolar shifts exhibited by backbone protons for the assigned residues conform well to those observed for other cyanomet globins and further support a conserved Mb fold. Perturbed medium-range dipolar contacts and the pH-independent backbone proton lability of the F helix are interpreted in terms of a holoprotein which is less stable than a conventional length globin.