Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
Border Biomedical Research Center, Department of Biological Sciences, University of Texas at El Paso, El Paso, TX, USA.
J Thromb Haemost. 2019 May;17(5):737-748. doi: 10.1111/jth.14412. Epub 2019 Mar 14.
Essentials Factor XIII is a heterotetramer with 2 catalytic A subunits and 2 non-catalytic B subunits. Structure of active and inactive factor XIII was studied with atomic force microscopy. Inactive factor XIII is made of an A globule and 2 flexible B subunits extending from it. Activated factor XIII separates into a B homodimer and 2 monomeric active A subunits. SUMMARY: Background Factor XIII (FXIII) is a precursor of the blood plasma transglutaminase (FXIIIa) that is generated by thrombin and Ca and covalently crosslinks fibrin to strengthen blood clots. Inactive plasma FXIII is a heterotetramer with two catalytic A subunits and two non-catalytic B subunits. Inactive A subunits have been characterized crystallographically, whereas the atomic structure of the entire FXIII and B subunits is unknown and the oligomerization state of activated A subunits remains controversial. Objectives Our goal was to characterize the (sub)molecular structure of inactive FXIII and changes upon activation. Methods Plasma FXIII, non-activated or activated with thrombin and Ca , was studied by single-molecule atomic force microscopy. Additionally, recombinant separate A and B subunits were visualized and compared with their conformations and dimensions in FXIII and FXIIIa. Results and Conclusions We showed that heterotetrameric FXIII forms a globule composed of two catalytic A subunits with two flexible strands comprising individual non-catalytic B subunits that protrude on one side of the globule. Each strand corresponds to seven to eight out of 10 tandem repeats building each B subunit, called sushi domains. The remainder were not seen, presumably because they were tightly bound to the globular A dimer. Some FXIII molecules had one or no visible strands, suggesting dissociation of the B subunits from the globular core. After activation of FXIII with thrombin and Ca , B subunits dissociated and formed B homodimers, whereas the activated globular A subunits dissociated into monomers. These results characterize the molecular organization of FXIII and changes with activation.
凝血因子 XIII 是一种由 2 个催化 A 亚基和 2 个非催化 B 亚基组成的杂四聚体。使用原子力显微镜研究了活性和非活性凝血因子 XIII 的结构。非活性凝血因子 XIII 由 A 球和从其延伸的 2 个柔性 B 亚基组成。激活的凝血因子 XIII 分离成 B 同源二聚体和 2 个单体活性 A 亚基。
凝血因子 XIII (FXIII) 是血浆转谷氨酰胺酶 (FXIIIa) 的前体，由凝血酶和 Ca 生成，并通过共价交联将纤维蛋白交联以增强血凝块。非活性血浆 FXIII 是一种由两个催化 A 亚基和两个非催化 B 亚基组成的杂四聚体。非活性 A 亚基已通过晶体学进行了表征，而整个 FXIII 和 B 亚基的原子结构未知，并且激活的 A 亚基的寡聚化状态仍存在争议。
我们的目标是表征非活性 FXIII 的（亚）分子结构及其在激活时的变化。
使用单分子原子力显微镜研究了血浆 FXIII、非激活或用凝血酶和 Ca 激活的 FXIII。此外，还对重组的单独 A 和 B 亚基进行了可视化，并将其构象与 FXIII 和 FXIIIa 中的构象和尺寸进行了比较。
我们表明，杂四聚体 FXIII 形成一个由两个催化 A 亚基组成的球，两个柔性链由单独的非催化 B 亚基组成，这些亚基在球的一侧突出。每个链对应于构建每个 B 亚基的 10 个串联重复中的 7 到 8 个，称为 sushi 结构域。其余部分没有被看到，可能是因为它们与球形 A 二聚体紧密结合。一些 FXIII 分子只有一个或没有可见的链，这表明 B 亚基从球形核心解离。用凝血酶和 Ca 激活 FXIII 后，B 亚基解离形成 B 同源二聚体，而激活的球形 A 亚基解离成单体。这些结果表征了 FXIII 的分子组织及其与激活的变化。
