Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI, USA.
Department of Pathology, Microbiology & Immunology, Vanderbilt University Medical Center, Nashville, TN, USA.
J Thromb Haemost. 2019 Dec;17(12):2131-2140. doi: 10.1111/jth.14612. Epub 2019 Sep 18.
Inorganic polyphosphate modulates the contact pathway of blood clotting, which is implicated in thrombosis and inflammation. Polyphosphate polymer lengths are highly variable, with shorter polymers (approximately 60-100 phosphates) secreted from human platelets, and longer polymers (up to thousands of phosphates) in microbes. We previously reported that optimal triggering of clotting via the contact pathway requires very long polyphosphates, although the impact of shorter polyphosphate polymers on individual proteolytic reactions of the contact pathway was not interrogated.
We conducted in vitro measurements of enzyme kinetics to investigate the ability of varying polyphosphate sizes, together with high molecular weight kininogen and Zn , to mediate four individual proteolytic reactions of the contact pathway: factor XII autoactivation, factor XII activation by kallikrein, prekallikrein activation by factor XIIa, and prekallikrein autoactivation.
The individual contact pathway reactions were differentially dependent on polyphosphate length. Very long-chain polyphosphate was required to support factor XII autoactivation, whereas platelet-size polyphosphate significantly accelerated the activation of factor XII by kallikrein, and the activation of prekallikrein by factor XIIa. Intriguingly, polyphosphate did not support prekallikrein autoactivation. We also report that high molecular weight kininogen was required only when kallikrein was the enzyme (ie, FXII activation by kallikrein), whereas Zn was required only when FXII was the substrate (ie, FXII activation by either kallikrein or FXIIa). Activation of prekallikrein by FXIIa required neither Zn nor high molecular weight kininogen.
Platelet polyphosphate and Zn can promote subsets of the reactions of the contact pathway, with implications for a variety of disease states.
无机多聚磷酸盐调节血液凝固的接触途径，这与血栓形成和炎症有关。多聚磷酸盐的聚合物长度变化很大，人类血小板分泌的短聚合物（约 60-100 个磷酸盐）和微生物中的长聚合物（多达数千个磷酸盐）。我们之前报道过，通过接触途径最佳触发凝血需要非常长的多聚磷酸盐，尽管尚未研究较短的多聚磷酸盐聚合物对接触途径中单个蛋白水解反应的影响。
我们进行了体外酶动力学测量，以研究不同多聚磷酸盐大小，以及高分子量激肽原和 Zn 的能力，来介导接触途径的四个单独的蛋白水解反应：因子 XII 自身激活、激肽释放酶激活因子 XII、因子 XIIa 激活前激肽酶和前激肽酶自身激活。
个别接触途径反应对多聚磷酸盐长度有不同的依赖性。非常长链的多聚磷酸盐是支持因子 XII 自身激活所必需的，而血小板大小的多聚磷酸盐显著加速了激肽释放酶对因子 XII 的激活，以及因子 XIIa 对前激肽酶的激活。有趣的是，多聚磷酸盐不支持前激肽酶的自身激活。我们还报告说，高分子量激肽原仅在激肽酶是酶（即因子 XII 被激肽酶激活）时才需要，而 Zn 仅在 FXII 是底物（即 FXII 被激肽酶或 FXIIa 激活）时才需要。FXIIa 对前激肽酶的激活既不需要 Zn 也不需要高分子量激肽原。
血小板多聚磷酸盐和 Zn 可以促进接触途径的反应子集，这对各种疾病状态有影响。
