Urwin P E, Atkinson H J, McPherson M J
Centre for Plant Biochemistry and Biotechnology, University of Leeds, UK.
Protein Eng. 1995 Dec;8(12):1303-7. doi: 10.1093/protein/8.12.1303.
Cystatins are small protein inhibitors of cysteine proteinases. The relative importance of the N-terminal region of cystatins, and of a conserved glycine within this region, remains unclear despite several studies. It was found that deletion of the N-terminal 21 amino acids abolishes the inhibitory capacity of oryzacystatin-I. The importance of a conserved glycine residue (Gly10) was also examined by replacing it with 11 other amino acids. Three further glycine residues (Gly5, -6 and -11) in this N-terminal region of oryzacystatin-I were similarly mutated. Only those variants in which Gly10 was substituted show any significant change in inhibitory capacity compared with wild-type oryzacystatin-I. The inhibitory characteristics of hybrid cystatin molecules comprising regions of chicken egg white cystatin and oryzacystatin were also examined. It is suggested that in common with animal cystatins, the N-terminal region of the plant cystatin, oryzacystatin-I, and in particular the highly conserved Gly10 residue are important for effective inhibition of papain.
胱抑素是半胱氨酸蛋白酶的小分子蛋白抑制剂。尽管有多项研究，但胱抑素N端区域以及该区域内一个保守甘氨酸的相对重要性仍不清楚。研究发现，缺失N端的21个氨基酸会消除水稻胱抑素-I的抑制能力。还通过将一个保守甘氨酸残基（Gly10）替换为其他11种氨基酸来研究其重要性。水稻胱抑素-I这个N端区域中的另外三个甘氨酸残基（Gly5、-6和-11）也进行了类似的突变。与野生型水稻胱抑素-I相比，只有那些Gly10被取代的变体在抑制能力上有任何显著变化。还研究了包含鸡卵清胱抑素和水稻胱抑素区域的杂合胱抑素分子的抑制特性。研究表明，与动物胱抑素一样，植物胱抑素水稻胱抑素-I的N端区域，特别是高度保守的Gly10残基，对有效抑制木瓜蛋白酶很重要。
