Negatively charged phospholipids stimulate factor XI activation by thrombin
Negatively charged phospholipids stimulate factor XI activation by thrombin
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DOI：
10.1016/j.tru.2020.100022
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
F. Omarova;J. Rosing;R. Bertina;E. Castoldi
中科院分区：
文献类型：
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作者：
F. Omarova;J. Rosing;R. Bertina;E. Castoldi
凝血因子XI(FXI)是丝氨酸蛋白酶FXIa的酶原，通过激活凝血因子IX参与凝血酶的形成。FXI可以被凝血因子XIIa或凝血酶激活，但凝血酶催化的FXI激活效率很低，除非被多阴离子如葡聚糖硫酸盐(DXS)或多聚磷酸(Polyp)刺激。目的研究带负电荷的磷脂是否也能促进凝血酶催化的FXI激活，并确定这种反应是否依赖于磷脂的浓度和组成、凝血酶外切酶和离子强度。利用特定的适配子探讨凝血酶外切体的作用。结果与DXS和息肉相似，含有高比例磷脂酸或磷脂酰丝氨酸的磷脂微囊可使凝血酶催化的FXI活性增强1-2个数量级。此外，在直接结合分析中，凝血酶和FXI与带负电荷的磷脂结合。两种凝血酶外切酶均能促进凝血酶与磷脂结合并激活FXI，且外切酶II占优势。无论是否存在磷脂，降低离子强度都能显著刺激凝血酶激活FXI。但在相同的离子强度下，与氯化钠的反应效率高于与四丙基氯化铵的反应效率，提示Na+的特异性刺激作用。结论负电荷磷脂与DXS和Polyp一样，通过凝血酶“模板机制”激活FXI。
IntroductionCoagulation factor XI (FXI) is the zymogen of the serine-protease FXIa, which contributes to thrombin formation by activating factor IX. FXI can be activated by factor XIIa or thrombin, but thrombin-catalysed FXI activation is highly inefficient, unless stimulated by polyanions such as dextran sulphate (DXS) or polyphosphate (PolyP).AimTo investigate whether negatively charged phospholipids can also enhance thrombin-catalysed FXI activation and to determine the dependence of this reaction on phospholipid concentration and composition, thrombin exosites and ionic strength.MethodsFXI was incubated with thrombin in the absence and presence of DXS, PolyP or phospholipid vesicles, and FXIa generation was followed using a chromogenic substrate. The role of thrombin exosites was probed using specific aptamers. The ionic strength was varied using either sodium chloride (NaCl) or tetrapropylammonium chloride.ResultsSimilar to DXS and PolyP, phospholipid vesicles with a high percentage of phosphatidic acid or phosphatidylserine enhanced thrombin-catalysed FXI activation by 1–2 orders of magnitude. Moreover, thrombin and FXI bound to negatively charged phospholipids in direct binding assays. Both thrombin exosites contributed to the ability of thrombin to bind to phospholipids and activate FXI, with a predominance of exosite II. Decreasing the ionic strength greatly stimulated FXI activation by thrombin, both in the absence and presence of phospholipids. However, at equal ionic strength, the reaction was more efficient with NaCl than with tetrapropylammonium chloride, suggesting a specific stimulatory effect of Na+.ConclusionsNegatively charged phospholipids, just as DXS and PolyP, stimulate FXI activation by thrombinviaa ‘template mechanism’.