Maskos K, Huber-Wunderlich M, Glockshuber R
Institut für Molekularbiologie und Biophysik, Eidgenössische Technische Hochschule Hönggerberg, Zürich, Switzerland.
FEBS Lett. 1996 Nov 11;397(1):11-6. doi: 10.1016/s0014-5793(96)01131-3.
The bifunctional inhibitor from Ragi (Eleusine coracana Gaertneri) (RBI) is the only member of the alpha-amylase/trypsin inhibitor family that inhibits both trypsin and alpha-amylase. Here, we show that both enzymes simultaneously and independently bind to RBI. The recently solved three-dimensional NMR structure of RBI has revealed that the inhibitor possesses a hitherto unknown fold for serine proteinase and alpha-amylase inhibitors. Despite its different fold, RBI obeys the standard mechanism observed for most protein inhibitors of serine proteinases and is a strong, competitive inhibitor of bovine trypsin (Ki = 1.2 +/- 0.2 nM). RBI is also a competitive inhibitor of porcine alpha-amylase (Ki = 11 +/- 2 nM) when a disaccharide is used as a substrate of alpha-amylase. However, the inhibition mode becomes complex when larger (> or = 7 saccharide units) alpha-amylase substrates are used. A second saccharide binding site on porcine alpha-amylase may enable larger oligosaccharides to displace RBI from its binding site in an intramolecular reaction.
来自龙爪稷（龙爪稷属，Eleusine coracana Gaertneri）的双功能抑制剂（RBI）是α-淀粉酶/胰蛋白酶抑制剂家族中唯一一种既能抑制胰蛋白酶又能抑制α-淀粉酶的成员。在此，我们表明这两种酶能同时且独立地与RBI结合。最近解析出的RBI的三维核磁共振结构显示，该抑制剂具有一种丝氨酸蛋白酶和α-淀粉酶抑制剂前所未知的折叠结构。尽管其折叠结构不同，但RBI遵循大多数丝氨酸蛋白酶蛋白抑制剂所观察到的标准机制，并且是牛胰蛋白酶的一种强效竞争性抑制剂（Ki = 1.2 ± 0.2 nM）。当使用二糖作为α-淀粉酶的底物时，RBI也是猪α-淀粉酶的竞争性抑制剂（Ki = 11 ± 2 nM）。然而，当使用更大（≥7个糖单元）的α-淀粉酶底物时，抑制模式会变得复杂。猪α-淀粉酶上的第二个糖结合位点可能使更大的寡糖在分子内反应中从其结合位点取代RBI。
