Follmer C, Barcellos G B, Zingali R B, Machado O L, Alves E W, Barja-Fidalgo C, Guimarães J A, Carlini C R
Department of Biophysics, IB, Universidade Federal Rio Grande do Sul, Av. Bento Gonçalves n degrees 9500, Porto Alegre, RS, CEP 91.501-970, Brazil.
Biochem J. 2001 Nov 15;360(Pt 1):217-24. doi: 10.1042/0264-6021:3600217.
Canatoxin is a toxic protein from Canavalia ensiformis seeds, lethal to mice (LD(50)=2 mg/kg) and insects. Further characterization of canatoxin showed that its main native form (184 kDa) is a non-covalently linked dimer of a 95 kDa polypeptide containing zinc and nickel. Partial sequencing of internal peptides indicated homology with urease (EC 3.5.1.5) from the same seed. Canatoxin has approx. 30% of urease's activity for urea, and K(m) of 2-7 mM. The proteins differ in their affinities for metal ions and were separated by affinity chromatography on a Zn(2+) matrix. Similar to canatoxin, urease activates blood platelets and interacts with glycoconjugates. In contrast with canatoxin, no lethality was seen in mice injected with urease (10 mg/kg). Pretreatment with p-hydroxymercuribenzoate irreversibly abolished the ureolytic activity of both proteins. On the other hand, p-hydroxymercuribenzoate-treated canatoxin was still lethal to mice, and both treated proteins were fully active in promoting platelet aggregation and binding to glycoconjugates. Taken together, our data indicate that canatoxin is a variant form of urease. Moreover, we show for the first time that these proteins display several biological effects that are unrelated to their enzymic activity for urea.
刀豆毒素是一种来自刀豆种子的有毒蛋白质，对小鼠（半数致死量=2毫克/千克）和昆虫具有致死性。对刀豆毒素的进一步表征表明，其主要天然形式（184千道尔顿）是一种95千道尔顿含锌和镍多肽的非共价连接二聚体。内部肽段的部分测序表明与来自同一种子的脲酶（EC 3.5.1.5）具有同源性。刀豆毒素对尿素具有约30%的脲酶活性，米氏常数为2-7毫摩尔。这两种蛋白质对金属离子的亲和力不同，并通过在锌离子基质上的亲和色谱法分离。与刀豆毒素相似，脲酶可激活血小板并与糖缀合物相互作用。与刀豆毒素不同，给小鼠注射脲酶（10毫克/千克）未观察到致死性。用对羟基汞苯甲酸预处理可不可逆地消除这两种蛋白质的尿素分解活性。另一方面，经对羟基汞苯甲酸处理的刀豆毒素对小鼠仍具有致死性，且两种处理后的蛋白质在促进血小板聚集和与糖缀合物结合方面均具有完全活性。综上所述，我们的数据表明刀豆毒素是脲酶的一种变体形式。此外，我们首次表明这些蛋白质表现出几种与其尿素酶活性无关的生物学效应。
