Coulombe R, Grochulski P, Sivaraman J, Ménard R, Mort J S, Cygler M
Biotechnology Research Institute, National Research Council of Canada, Montreal, Quebec.
EMBO J. 1996 Oct 15;15(20):5492-503.
Cathepsin L is a member of the papain superfamily of cysteine proteases and, like many other proteases, it is synthesized as an inactive proenzyme. Its prosegment shows little homology to that of procathepsin B, whose structure, the first for a cysteine protease proenzyme, has been determined recently. We report here the 3-D structure of a mutant of human procathepsin L determined at 2.2 A resolution, describe the mode of binding employed by the prosegment and discuss the molecular basis for other possible roles of the prosegment. The N-terminal part of the prosegment is globular and contains three alpha-helices with a small hydrophobic core built around aromatic side chains. This domain packs against a loop on the enzyme's surface, with the aromatic side chain from the prosegment being located in the center of this loop and providing a large contact area. The C-terminal portion of the prosegment assumes an extended conformation and follows along the substrate binding cleft toward the N-terminus of the mature enzyme. The direction of the prosegment in the substrate binding cleft is opposite to that of substrates. The previously described role of the prosegment in the interactions with membranes is supported by the structure of its N-terminal domain. The fold of the prosegment and the mechanism by which it inhibits the enzymatic activity of procathepsin L is similar to that observed in procathepsin B despite differences in length and sequence, suggesting that this mode of inhibition is common to all enzymes from the papain superfamily.
组织蛋白酶L是半胱氨酸蛋白酶木瓜蛋白酶超家族的成员，与许多其他蛋白酶一样，它以无活性的酶原形式合成。其前肽与组织蛋白酶B原的前肽几乎没有同源性，组织蛋白酶B原的结构是首个被确定的半胱氨酸蛋白酶原的结构，最近已被确定。我们在此报告了分辨率为2.2埃的人组织蛋白酶L原突变体的三维结构，描述了前肽所采用的结合模式，并讨论了前肽其他可能作用的分子基础。前肽的N端部分呈球状，包含三个α螺旋，围绕芳香族侧链形成一个小的疏水核心。该结构域与酶表面的一个环紧密结合，前肽的芳香族侧链位于该环的中心并提供了较大的接触面积。前肽的C端部分呈伸展构象，沿着底物结合裂隙向成熟酶的N端延伸。前肽在底物结合裂隙中的方向与底物相反。前肽N端结构域的结构支持了其先前所述的与膜相互作用的作用。尽管长度和序列存在差异，但前肽的折叠及其抑制组织蛋白酶L原酶活性的机制与组织蛋白酶B原中观察到的相似，这表明这种抑制模式在木瓜蛋白酶超家族的所有酶中是常见的。
