CRYSTALLOGRAPHIC STUDIES OF PROKARYOTIC RNA POLYMERASE

纤维蛋白原是血液中发现的一种大的糖蛋白， 变成不溶性聚合物，称为纤维蛋白， 凝血酶的催化作用。 转型 通过从氨基末端去除小肽 纤维蛋白原中两条不同的链，暴露出两个新的氨基末端 序列的 新暴露的两端被称为“旋钮”， 插入到其它分子的羧基末端附近的互补位点（“孔”）中， 纤维蛋白原分子。 对应于“旋钮”的合成肽 与纤维蛋白原结合，但仅与两者之一结合（A结= Gly-Pro-Arg-X） 有效防止纤维蛋白形成。 另一种肽 （B结= Gly-His-Arg-X）与纤维蛋白原结合但不阻断 聚合法 纤维蛋白原和纤维蛋白可以分解成大的 摩尔 重量 各种蛋白酶的核心片段。 其中最大的 片段被称为片段D，并且已知它结合合成的 肽节 我们最近报道了片段D的结构， 人纤维蛋白原，以及来自纤维蛋白的双-D（Spraggon et 等人，Nature，389：455-462，1997）。 当时，我们只能 在一种（合成的） A-旋钮。 去年，我们成功地在有 都是合成肽 我们来到国际象棋，管理一个完整的数据， 分辨率为2.3 A。 发现这两种肽与两种 不同但同源的位点。 这是第一次直接 证明Gly-His-Arg旋钮可以插入 β链对应于γ链上的一个空穴， 甘氨酸-脯氨酸-精氨酸 这两个孔的方向相反， 这解释了为什么聚合只能被A型旋钮阻止。 的 B结明显累及次级（外侧）。 协会. 该结构还揭示了一个弱结合的钙离子附近的 β链孔，解释了一个长期存在的谜团，为什么钙 影响B旋钮的结合。 这项工作目前正在印刷中 《生物化学》，定于1998年7月初出版。

Fibrinogen is a large glycoprotein found in the blood which becomes transformed into the insoluble polymer called fibrin under the catalytic influence of the enzyme thrombin. The transformation is brought about by the removal of small peptides from the amino-termini of two different chains in fibrinogen, exposing two new amino-terminal sequences. The newly exposed ends dubbed "knobs," were thought to fit into complementary sites ("holes") near the carboxyl-termini of other fibrinogen molecules. Synthetic peptides corresponding to the "knobs" bind to fibrinogen, but only one of the two (A-knob = Gly-Pro-Arg-X) is effective in preventing fibrin formation. The other peptide (B-knob = Gly-His-Arg-X) binds to fibrinogen but does not block polymerization. Fibrinogen and fibrin can be broken down into large mol. wt. core fragments by various proteases. The largest of these fragments is called fragment D, and it is known to bind the synthetic peptide knobs. We recently reported the structure of fragment D, from human fibrinogen, and also that of double-D from fibrin (Spraggon et al, Nature, 389:455-462, 1997). At the time, we had only been able to crystallize the latter in the presence of one of the (synthetic) A-knob. Last year we succeeded in growing crystals in the presence of both synthetic peptides. We came to CHESS and managed a complete data set at 2.3 A resolution. The two peptides were found bound to two different but homologous sites. This was the first direct demonstration that the Gly-His-Arg-knob fit into a hole on the beta-chain corresponding to a hole on the gamma-chain that binds Gly-Pro-Arg. The two holes are aimed in opposite directions, explaining why polymerization is only prevented by the A-knob. The B-knob is apparently involved in secondary (lateral). associations. The structure also revealed a weakly bound calcium ion near the beta-chain hole, explaining a longstanding mystery of why calcium influences the binding of the B-knob. This work is currently in press in Biochemistry, schedule for publication in early July, 1998.