CRYSTALLOGRAPHIC STUDIES OF PROKARYOTIC RNA POLYMERASE

纤维蛋白原是一种在血液中发现的大糖蛋白，它 会转化为一种叫做纤维蛋白的不溶性聚合物 凝血酶的催化作用。这一转变是 由去掉氨基末端的小肽引起的 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。新露出的两端被称为“旋钮”，被认为符合 进入互补的位置(“洞”)附近的羧基末端 纤维蛋白原分子。与“旋钮”相对应的合成肽 与纤维蛋白原结合，但只与其中一种结合(A旋钮=Gly-Pro-Arg-X) 在防止纤维蛋白形成方面很有效。另一种多肽 (B-旋钮=Gly-His-Arg-X)与纤维蛋白原结合但不阻断 聚合反应。纤维蛋白原和纤维蛋白可以分解成大的 摩尔。不同类型的蛋白水解酶的重量核心片段。其中最大的一个 片断被称为片断D，已知的是将合成的 多肽旋钮。我们最近报道了片段D的结构，来自 人纤维蛋白原，以及来自纤维蛋白的双D(Spraggon et 《自然》，389：455-462,1997)。当时，我们只能 在其中一种(合成的)存在下使后者结晶 A旋钮。去年，我们成功地在 两种都是合成肽。我们来下棋，管理了一个完整的数据 将分辨率设置为2.3 A。这两个多肽被发现与两个 不同但相同的地点。这是第一次直接 演示Gly-His-Arg旋钮是否适合安装在 与结合的伽马链上的空洞相对应的β链 Gly-Pro-Arg两个洞指向相反的方向， 解释了为什么只有A型旋钮才能防止聚合。这个 B-旋钮明显参与次级(侧方)。联想。 该结构还揭示了在接近于 贝塔链空洞，解释了为什么钙 影响B旋钮的绑定。这部作品目前正在出版中。 《生物化学》，计划于1998年7月初发表。

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.