Determinants of protein hydrogen exchange studied in equine cytochrome c
Determinants of protein hydrogen exchange studied in equine cytochrome c
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研究马细胞色素 c 蛋白氢交换的决定因素
DOI：
10.1002/pro.5560070323
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发表时间：
1998-03-01
期刊：
影响因子：
8
通讯作者：
Englander, SW
中科院分区：
文献类型：
--
作者：
Milne, JS;Mayne, L;Englander, SW
用核磁共振法测定了氧化马细胞色素c中大量酰胺氢的交换，并与结构参数进行了比较。分别考虑了已知通过局部结构波动和通过较大的展开反应进行交换的氢。通过大于10（3）的因子保护免于交换的所有氢处于确定的H键中，并且几乎所有H键合的氢（包括在蛋白质表面的那些）被测量为缓慢交换。H-交换速率与H-键强度（长度）或晶体学B因子无关。看来，使可交换的氢与H-交换催化剂（OH-离子）形成H-键接触所必需的瞬态结构波动涉及到H-键供体和受体的相当大的分离，至少几埃，因此取决于紧邻结构的相对抗变形性。因此，对于被紧密锚定的结构所包围的氢和被很好地掩埋的氢，通过局部波动途径的H交换往往非常缓慢。埋氢的减慢也可能反映了一旦保护H键被分离，允许溶剂进入的额外运动的需要，尽管值得注意的是，在蛋白质如细胞色素c中的埋不超过4埃。当局部波动路径非常缓慢时，交换可以被不同类别的更大的、合作的、分段的展开反应所主导，这些反应可以达到全球展开。
The exchange of a large number of amide hydrogens in oxidized equine cytochrome c was measured by NMR and compared with structural parameters. Hydrogens known to exchange through local structural fluctuations and through larger unfolding reactions were separately considered. All hydrogens protected from exchange by factors greater than 10(3) are in defined H-bonds, and almost all H-bonded hydrogens including those at the protein surface were measured to exchange slowly. H-exchange rates do not correlate with H-bond strength (length) or crystallographic B factors. It appears that the transient structural fluctuation necessary to bring an exchangeable hydrogen into H-bonding contact with the H-exchange catalyst (OH--ion) involves a fairly large separation of the H-bond donor and acceptor, several angstroms at least, and therefore depends on the relative resistance to distortion of immediately neighboring structure. Accordingly, H-exchange by way of local fluctuational pathways tends to be very slow for hydrogens that are neighbored by tightly anchored structure and for hydrogens that are well buried. The slowing of buried hydrogens may also reflect the need for additional motions that allow solvent access once the protecting H-bond is separated, although it is noteworthy that burial in a protein like cytochrome c does not exceed 4 Angstrom. When local fluctuational pathways are very slow, exchange can become dominated by a different category of larger, cooperative, segmental unfolding reactions reaching up to global unfolding.