Rath V L, Lin K, Hwang P K, Fletterick R J
Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448, USA.
Structure. 1996 Apr 15;4(4):463-73. doi: 10.1016/s0969-2126(96)00051-2.
Glycogen phosphorylases consist of a conserved catalytic core onto which different regulatory sites are added. By comparing the structures of isozymes, we hope to understand the structural principles of allosteric regulation in this family of enzymes. Here, we focus on the differences in the glucose 6-phosphate (Glc-6-P) binding sites of two isozymes.
We have refined the structure of Glc-6-P inhibited yeast phosphorylase b to 2.6 A and compared it with known structures of muscle phosphorylase. Glc-6-P binds in a novel way, interacting with a distinct set of secondary elements. Structural links connecting the Glc-6-P binding sites and catalytic sites are conserved, although the specific contacts are not.
Our comparison reveals that the Glc-6-P binding site was modified over the course of evolution from yeast to vertebrates to become a bi-functional switch. The additional ability of muscle phosphorylase to be activated by AMP required the recruitment of structural elements into the binding site and sequence changes to create a binding subsite for adenine, whilst maintaining links to the catalytic site.
糖原磷酸化酶由一个保守的催化核心和添加在其上的不同调节位点组成。通过比较同工酶的结构，我们希望了解该酶家族中变构调节的结构原理。在此，我们聚焦于两种同工酶的6-磷酸葡萄糖（Glc-6-P）结合位点的差异。
我们已将Glc-6-P抑制的酵母磷酸化酶b的结构精修至2.6埃，并将其与肌肉磷酸化酶的已知结构进行比较。Glc-6-P以一种新的方式结合，与一组独特的二级结构元件相互作用。连接Glc-6-P结合位点和催化位点的结构连接是保守的，尽管具体的接触并非如此。
我们的比较表明，从酵母到脊椎动物的进化过程中，Glc-6-P结合位点发生了改变，成为一个双功能开关。肌肉磷酸化酶被AMP激活的额外能力需要将结构元件招募到结合位点并发生序列变化，以创建一个腺嘌呤结合亚位点，同时保持与催化位点的连接。
