Lipkind G, Steiner D F
Department of Biochemistry and Molecular Biology, The Howard Hughes Medical Institute, The University of Chicago, Illinois 60637, USA.
Biochemistry. 1999 Jan 19;38(3):890-6. doi: 10.1021/bi981556q.
The intracellular conversion of proinsulin to insulin occurs via cleavage at the two dibasic sites: Arg31-Arg32, B chain-C-peptide (BC) junction; and Lys64-Arg65, A chain-C-peptide (CA) junction, catalyzed by the subtilisin-like prohormone convertases SPC3 (PC1/PC3) and SPC2 (PC2), respectively. In this report we propose a possible conformational variant of proinsulin that would facilitate the formation of enzyme-substrate complexes at the BC and AC junctions of proinsulin with the substrate binding groove of the two closely related convertases. Productive convertase interaction requires extended peptide conformations in both the CA junction (residues 62-67, LQKRGI) and the BC junction (residues 29-34, KTRREA) and leads to significant perturbations in the normally alpha-helical N-terminal region of the A chain and the extended C-terminal region of the B chain of the insulin moiety of proinsulin. In this model of the reactive conformation of human proinsulin, both processing sites assume positions that are relatively far apart. The C-peptide was then modeled in an unobtrusive conformation relative to the convertases and the remainder of the substrate, forming an extended loop of length approximately 40 A with a short alpha-helical segment rather than a random coil. A model of the stereochemical transformations that occur during the processing of proinsulin by SPC2 is presented.
精氨酸31 - 精氨酸32，B链 - C肽（BC）连接处；以及赖氨酸64 - 精氨酸65，A链 - C肽（CA）连接处，分别由枯草杆菌蛋白酶样激素原转化酶SPC3（PC1 / PC3）和SPC2（PC2）催化。在本报告中，我们提出了一种胰岛素原可能的构象变体，它将促进胰岛素原在BC和AC连接处与两种密切相关转化酶的底物结合凹槽形成酶 - 底物复合物。有效的转化酶相互作用需要CA连接处（残基62 - 67，LQKRGI）和BC连接处（残基29 - 34，KTRREA）都有延伸的肽构象，并导致胰岛素原胰岛素部分的A链正常α螺旋N端区域和B链延伸C端区域出现显著扰动。在这个人类胰岛素原反应性构象模型中，两个加工位点处于相对较远的位置。然后，相对于转化酶和底物的其余部分，C肽以一种不显眼的构象建模，形成一个长度约为40埃的延伸环，带有一个短的α螺旋段而不是无规卷曲。本文展示了SPC2处理胰岛素原过程中发生的立体化学转变模型。
