Bell J E, Cunningham E, Belt C, Featherstone J D, Bell J
Biochemistry Program, Gustavus Adolphus College, St Peter, MN 56082, USA.
Arch Oral Biol. 1997 Oct-Nov;42(10-11):761-72. doi: 10.1016/s0003-9969(97)00007-1.
The cystatin family of proteins exists in both excreted and intracellular forms, and appears to be involved in protective and regulatory roles, inhibiting a variety of bacterial, viral and intracellular proteases. The amino acid sequences of several human forms of cystatin are known, but currently only the structure of chicken cystatin (approx. 40% homologous to the human forms) has been experimentally determined. The objective of this study was to use the X-ray coordinates of chicken cystatin to construct computer models of the structures of three human salivary forms (SN, S and SA). These structures were energy-minimized and subjected to dynamic simulations. The resultant structures were compared to determine conformational differences. Global root mean square deviations between equivalent atoms ranged from 1.4 A to 3.9 A. The closest structural similarity to chicken cystatin involved cystatin SN, which also showed the highest (68%) functional sequence homology. Local secondary structure was examined in more detail. In comparisons of alpha-carbon position the third beta-strand (77% functional sequence conservation) and its preceding loop (60% conserved) showed the highest structural conservation in S, while beta-strand 4 showed the highest structural conservation in SN and SA. Throughout their structures, SN and SA were more structurally similar to chicken cystatin than to salivary cystatin S. There are two regions of conserved, negatively charged residues in the salivary cystatins, which appear to be spaced so that they are capable of interaction with hydroxypatite. It is concluded that not only does structural modelling by analogy provide detailed models of salivary cystatins that can be tested by future experimentation, but also that examination of the models has revealed potential sites of interaction with hydroxyapatite.
胱抑素蛋白家族以分泌型和细胞内型两种形式存在，似乎具有保护和调节作用，可抑制多种细菌、病毒和细胞内蛋白酶。几种人类胱抑素的氨基酸序列已为人所知，但目前仅通过实验确定了鸡胱抑素的结构（与人类形式约40%同源）。本研究的目的是利用鸡胱抑素的X射线坐标构建三种人类唾液型（SN、S和SA）结构的计算机模型。对这些结构进行能量最小化处理并进行动态模拟。比较所得结构以确定构象差异。等效原子之间的全局均方根偏差范围为1.4埃至3.9埃。与鸡胱抑素结构最相似的是胱抑素SN，其功能序列同源性也最高（68%）。对局部二级结构进行了更详细的研究。在α-碳位置的比较中，第三条β链（功能序列保守性77%）及其前面的环（保守性60%）在S中显示出最高的结构保守性，而β链4在SN和SA中显示出最高的结构保守性。在整个结构中，SN和SA与鸡胱抑素的结构相似性高于与唾液胱抑素S的相似性。唾液胱抑素中有两个保守的带负电荷残基区域，其间隔似乎使其能够与羟基磷灰石相互作用。得出的结论是，类比结构建模不仅提供了可通过未来实验进行测试的唾液胱抑素详细模型，而且对模型的研究还揭示了与羟基磷灰石相互作用的潜在位点。
