Shen Linnan, Tatham Michael H, Dong Changjiang, Zagórska Anna, Naismith James H, Hay Ronald T
Centre for Interdisciplinary Research, School of Life Science, University of Dundee, DD1 5EH, UK.
Nat Struct Mol Biol. 2006 Dec;13(12):1069-77. doi: 10.1038/nsmb1172. Epub 2006 Nov 12.
Small ubiquitin-like modifier (SUMO)-specific protease SENP1 processes SUMO-1, SUMO-2 and SUMO-3 to mature forms and deconjugates them from modified proteins. To establish the proteolytic mechanism, we determined structures of catalytically inactive SENP1 bound to SUMO-1-modified RanGAP1 and to unprocessed SUMO-1. In each case, the scissile peptide bond is kinked at a right angle to the C-terminal tail of SUMO-1 and has the cis configuration of the amide nitrogens. SENP1 preferentially processes SUMO-1 over SUMO-2, but binding thermodynamics of full-length SUMO-1 and SUMO-2 to SENP1 and K(m) values for processing are very similar. However, k(cat) values differ by 50-fold. Thus, discrimination between unprocessed SUMO-1 and SUMO-2 by SENP1 is based on a catalytic step rather than substrate binding and is likely to reflect differences in the ability of SENP1 to correctly orientate the scissile bonds in SUMO-1 and SUMO-2.
小泛素样修饰物（SUMO）特异性蛋白酶SENP1将SUMO-1、SUMO-2和SUMO-3加工成成熟形式，并将它们从修饰蛋白上解离下来。为了确定其蛋白水解机制，我们测定了与SUMO-1修饰的RanGAP1以及未加工的SUMO-1结合的无催化活性的SENP1的结构。在每种情况下，可裂解肽键与SUMO-1的C末端尾巴呈直角弯曲，并且酰胺氮具有顺式构型。SENP1对SUMO-1的加工优先于SUMO-2，但全长SUMO-1和SUMO-2与SENP1的结合热力学以及加工的米氏常数（Km）值非常相似。然而，催化常数（kcat）值相差50倍。因此，SENP1对未加工的SUMO-1和SUMO-2的区分基于催化步骤而非底物结合，并且可能反映了SENP1正确定向SUMO-1和SUMO-2中可裂解键的能力差异。
