Ghosh Madhumita, Shanker Sreejesh, Siwanowicz Igor, Mann Karlheinz, Machleidt Werner, Holak Tad A
Max Planck Institute for Biochemistry, D-82152 Martinsried, Germany.
Biol Chem. 2005 Jan;386(1):85-93. doi: 10.1515/BC.2005.011.
Calpains are non-lysosomal, Ca 2+ -dependent cysteine proteases, which are ubiquitously distributed across cell types and vertebrate species. The rules that govern calpain specificity have not yet been determined. To elucidate the cleavage pattern of calpains, we carried out calpain-induced proteolytic studies on the insulin-like growth factor binding proteins IGFBP-4 and -5. Proteolysis of IGFBPs is well characterized in numerous reports. Our results show that calpain cleavage sites are in the non-conserved unstructured regions of the IGFBPs. Compilation of the calpain-induced proteolytic cleavage sites in several proteins reported in the literature, together with our present study, has not revealed clear preferences for amino acid sequences. We therefore conclude that calpains seem not to recognize amino acid sequences, but instead cleave with low sequence specificity at unstructured or solvent-exposed fragments that connect folded, stable domains of target proteins.
钙蛋白酶是一种非溶酶体的、依赖钙离子的半胱氨酸蛋白酶，广泛分布于各种细胞类型和脊椎动物物种中。目前尚未确定决定钙蛋白酶特异性的规则。为了阐明钙蛋白酶的切割模式，我们对胰岛素样生长因子结合蛋白IGFBP - 4和 - 5进行了钙蛋白酶诱导的蛋白水解研究。在众多报告中，IGFBP的蛋白水解已有详细描述。我们的结果表明，钙蛋白酶的切割位点位于IGFBP的非保守无结构区域。结合文献中报道的几种蛋白质的钙蛋白酶诱导的蛋白水解切割位点以及我们目前的研究，尚未发现对氨基酸序列有明显偏好。因此，我们得出结论，钙蛋白酶似乎不识别氨基酸序列，而是以低序列特异性在连接靶蛋白折叠稳定结构域的无结构或溶剂暴露片段处进行切割。
