Inhibitory plant serpins with a sequence of three glutamine residues in the reactive center
Inhibitory plant serpins with a sequence of three glutamine residues in the reactive center
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DOI：
10.1515/bc.2005.150
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发表时间：
2005-12-01
影响因子：
3.7
通讯作者：
Hejgaard, J
中科院分区：
文献类型：
--
作者：
Hejgaard, J
丝氨酸蛋白酶抑制剂似乎普遍存在于除真菌外的真核生物中，并且也存在于一些细菌、古细菌和病毒中。具有谷氨酰胺作为反应中心P1残基的抑制性丝氨酸蛋白酶抑制剂仅在少数植物物种中被鉴定。从大麦和小麦中分别分离到一种独特的丝氨酸蛋白酶抑制剂，其反应中心序列为P3-P1或P2-P1'上的三个Gln残基。大麦BSZ 3是胰凝乳蛋白酶的不可逆抑制剂，复合物形成的二级缔合速率常数k（a）'约为10（4）M-1 s（-1）;然而，只有一小部分丝氨酸蛋白酶抑制剂分子与胰凝乳蛋白酶反应，大部分对反应中心环中的裂解不敏感。小麦WSZ 3在P8 Thr处特异性切割，并且不是胰凝乳蛋白酶的抑制剂。这些反应中心的循环可能已经演变的构象，是最佳的抑制性诱饵蛋白酶，专门降解含有谷氨酰胺丰富的重复序列的存储醇溶蛋白，最有可能的昆虫害虫或真菌病原体的消化蛋白酶感染谷物。组装的棉铃纤维中表达的丝氨酸蛋白酶抑制剂（GaZ 1）的全长氨基酸序列包括丝氨酸蛋白酶抑制剂-蛋白酶相互作用所必需的保守区域，表明在具有四个Gln残基的序列的推定反应中心P2-P2'处具有抑制能力。
Serpins appear to be ubiquitous in eukaryotes, except fungi, and are also present in some bacteria, archaea and viruses. Inhibitory serpins with a glutamine as the reactive-center P1 residue have been identified exclusively in a few plant species. Unique serpins with a reactive center sequence of three Gln residues at P3-P1 or P2-P1' were isolated from barley and wheat grain, respectively. Barley BSZ3 was an irreversible inhibitor of chymotrypsin, with a second-order association rate constant for complex formation k(a)' of the order of 10(4) M-1 s(-1) ; however, only a minor fraction of the serpin molecules reacted with chymotrypsin, with the majority insensitive to cleavage in the reactive center loop. Wheat WSZ3 was cleaved specifically at P8 Thr and was not an inhibitor of chymotrypsin. These reactive-center loops may have evolved conformations that are optimal as inhibitory baits for proteinases that specifically degrade storage prolamins containing Gln-rich repetitive sequences, most likely for digestive proteinases of insect pests or fungal pathogens that infect cereals. An assembled full-length amino acid sequence of a serpin expressed in cotton boll fiber (GaZ1) included conserved regions essential for serpin-proteinase interaction, suggesting inhibitory capacity at a putative reactive center P2-P2' with a sequence of four Gln residues.