Singh Sneha, Hagelueken Gregor, Ugurlar Deniz, Ramaraje Urs Samhitha Urs, Sharma Amit, Mahapatra Manoranjan, Drepper Friedel, Imhof Diana, Huesgen Pitter F, Oldenburg Johannes, Geyer Matthias, Biswas Arijit
Arijit Biswas Laboratory, Institute for Experimental Hematology and Transfusion Medicine, University Hospital Bonn, Bonn, Germany.
Institute of Structural Biology, University of Bonn, Bonn, Germany.
Blood. 2025 Jan 23;145(4):438-449. doi: 10.1182/blood.2024025369.
The structure of human coagulation factor XIII (FXIII), a heterotetrameric plasma protransglutaminase that covalently cross-links preformed fibrin polymers, remains elusive until today. The heterotetrameric complex is composed of 2 catalytic FXIII-A and 2 protective FXIII-B subunits. Structural etiology underlying FXIII deficiency has so far been derived from crystallographic structures, all of which are currently available for the FXIII-A2 homodimer only. Here, we present the cryogenic electron microscopy (cryo-EM) structure of a native, human plasma-derived FXIII-A2B2 complex at 2.4 Å resolution. The structure provides detailed information on FXIII subunit interacting interfaces as the 2 subunits interact strongly in plasma. The native FXIII-A2B2 complex reveals a pseudosymmetric heterotetramer of 2 FXIII-B monomers intercalating with a symmetric FXIII-A2 dimer forming a "crown"-like assembly. The symmetry axes of the A2 and B2 homodimers are twisted relative to each other such that Sushi domain 1 interacts with the catalytic core of the A subunit, and Sushi domain 2 with the symmetry related A' subunit, and vice versa. We also report 4 novel mutations in the F13A1 gene encoding the FXIII-A subunit from a cohort of patients with severe FXIII deficiency. Our structure reveals the etiological basis of homozygous and heterozygous pathogenic mutations and explains the conditional dominant negative effects of heterozygous mutations. This atomistic description of complex interfaces is consistent with previous biochemical data and shows a congruence between the structural biochemistry of the FXIII complex and the clinical features of FXIII deficiency.
人凝血因子XIII（FXIII）是一种异源四聚体血浆前转谷氨酰胺酶，可共价交联预先形成的纤维蛋白聚合物，其结构至今仍不清楚。该异源四聚体复合物由2个催化性FXIII-A亚基和2个保护性FXIII-B亚基组成。迄今为止，FXIII缺乏症的结构病因学来源于晶体学结构，目前所有这些结构仅适用于FXIII-A2同型二聚体。在此，我们展示了源自人血浆的天然FXIII-A2B2复合物在2.4Å分辨率下的低温电子显微镜（cryo-EM）结构。该结构提供了关于FXIII亚基相互作用界面的详细信息，因为这两个亚基在血浆中强烈相互作用。天然FXIII-A2B2复合物显示为一个假对称异源四聚体，由2个FXIII-B单体插入一个对称的FXIII-A2二聚体中，形成一个“皇冠”状组装体。A2和B2同型二聚体的对称轴彼此扭曲，使得寿司结构域1与A亚基的催化核心相互作用，寿司结构域2与对称相关的A'亚基相互作用，反之亦然。我们还报告了来自一组严重FXIII缺乏症患者的F13A1基因（编码FXIII-A亚基）中的4个新突变。我们的结构揭示了纯合和杂合致病突变的病因学基础，并解释了杂合突变的条件性显性负效应。这种对复合物界面的原子水平描述与先前的生化数据一致，并显示了FXIII复合物的结构生物化学与FXIII缺乏症临床特征之间的一致性。
