Law Ruby H P, Irving James A, Buckle Ashley M, Ruzyla Katya, Buzza Marguerite, Bashtannyk-Puhalovich Tanya A, Beddoe Travis C, Nguyen Kim, Worrall D Margaret, Bottomley Stephen P, Bird Phillip I, Rossjohn Jamie, Whisstock James C
The Protein Crystallography Unit, Monash Centre for Synchrotron Science and The Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Faculty of Medicine, Monash University, Clayton, Victoria 3800, Australia.
J Biol Chem. 2005 Jun 10;280(23):22356-64. doi: 10.1074/jbc.M412043200. Epub 2005 Mar 10.
Maspin is a serpin that acts as a tumor suppressor in a range of human cancers, including tumors of the breast and lung. Maspin is crucial for development, because homozygous loss of the gene is lethal; however, the precise physiological role of the molecule is unclear. To gain insight into the function of human maspin, we have determined its crystal structure in two similar, but non-isomorphous crystal forms, to 2.1- and 2.8-A resolution, respectively. The structure reveals that maspin adopts the native serpin fold in which the reactive center loop is expelled fully from the A beta-sheet, makes minimal contacts with the core of the molecule, and exhibits a high degree of flexibility. A buried salt bridge unique to maspin orthologues causes an unusual bulge in the region around the D and E alpha-helices, an area of the molecule demonstrated in other serpins to be important for cofactor recognition. Strikingly, the structural data reveal that maspin is able to undergo conformational change in and around the G alpha-helix, switching between an open and a closed form. This change dictates the electrostatic character of a putative cofactor binding surface and highlights this region as a likely determinant of maspin function. The high resolution crystal structure of maspin provides a detailed molecular framework to elucidate the mechanism of function of this important tumor suppressor.
乳腺丝抑蛋白是一种丝氨酸蛋白酶抑制剂，在包括乳腺癌和肺癌在内的多种人类癌症中发挥肿瘤抑制作用。乳腺丝抑蛋白对发育至关重要，因为该基因的纯合缺失是致死性的；然而，该分子的确切生理作用尚不清楚。为深入了解人类乳腺丝抑蛋白的功能，我们分别以2.1埃和2.8埃的分辨率，确定了其两种相似但非同晶型晶体形式的晶体结构。该结构表明，乳腺丝抑蛋白采用天然丝氨酸蛋白酶抑制剂折叠方式，其中反应中心环完全从Aβ片层中排出，与分子核心的接触最少，并表现出高度的灵活性。乳腺丝抑蛋白直向同源物特有的一个埋藏盐桥在D和Eα螺旋周围区域导致一个不寻常的凸起，在其他丝氨酸蛋白酶抑制剂中已证明该分子区域对辅因子识别很重要。引人注目的是，结构数据表明，乳腺丝抑蛋白能够在Gα螺旋及其周围发生构象变化，在开放和封闭形式之间切换。这种变化决定了假定的辅因子结合表面的静电特性，并突出了该区域作为乳腺丝抑蛋白功能的一个可能决定因素。乳腺丝抑蛋白的高分辨率晶体结构提供了一个详细的分子框架，以阐明这种重要肿瘤抑制因子的功能机制。
