Hymas Preston P, Conboy John C
Department of Chemistry, University of Utah, 315 S. 1400 E. RM 2020, Salt Lake City, UT 84112, USA.
Faraday Discuss. 2025 Aug 13;259(0):384-415. doi: 10.1039/d4fd00206g.
Ca ions are believed to play a crucial role in regulating lipid membrane asymmetry by modulating the activity of flippases, floppases, and scramblases. Dysregulation of Ca homeostasis, and subsequent loss of phosphatidylserine (PS) lipid asymmetry, is associated with physiological conditions such as blood clotting, neurodegeneration, and apoptosis. Yet, despite the prominence of Ca with regards to PS flip-flop, the specific actions of Ca are not fully understood and detailed mechanisms remain elusive. Much focus has been placed on enzymatic interactions, while the endogenous interactions of Ca ions with PS and the direct role Ca ions play on maintaining PS asymmetry have not been characterized in detail, a potentially crucial gap in understanding. In the current study the binding affinities of Ca ions to planar supported lipid membranes containing PS were measured sum-frequency vibrational spectroscopy (SFVS). Evaluation of binding affinity obtained from SFVS peak area analysis yielded an affinity of 1.3 × 10 M. The rate of PS flip-flop was also measured in the presence and absence of Ca SFVS, with a nearly five-fold decrease in the rate of translocation when Ca ions are present. Controls which tested Mg with PS or phosphatidylcholine (PC) with Ca did not show similar slowing effects, highlighting the specificity of the PS-Ca interaction. For the binary lipid mixture tested, the disparity in the PS flip-flop rate would be sufficient to produce an 82% PS asymmetry if Ca ions are localized to one side of the membrane. These studies have important implications for the non-enzymatic role Ca ions may play in the maintenance of PS asymmetry.
钙离子被认为在通过调节翻转酶、转位酶和磷脂翻转酶的活性来调节脂质膜不对称性方面发挥着关键作用。钙稳态失调以及随后磷脂酰丝氨酸（PS）脂质不对称性的丧失与诸如血液凝固、神经退行性变和细胞凋亡等生理状况相关。然而，尽管钙在PS翻转方面很突出，但钙的具体作用尚未完全了解，详细机制仍然难以捉摸。人们将很多注意力放在了酶促相互作用上，而钙离子与PS的内源性相互作用以及钙离子在维持PS不对称性中所起的直接作用尚未得到详细表征，这是理解上一个潜在的关键差距。在当前研究中，通过和频振动光谱法（SFVS）测量了钙离子与含有PS的平面支撑脂质膜的结合亲和力。从SFVS峰面积分析获得的结合亲和力评估得出亲和力为1.3×10 M。还在有和没有钙离子的情况下通过SFVS测量了PS翻转的速率，当存在钙离子时，转位速率下降了近五倍。用镁与PS或钙与磷脂酰胆碱（PC）进行测试的对照未显示出类似的减缓作用，突出了PS - 钙相互作用的特异性。对于所测试的二元脂质混合物，如果钙离子定位于膜的一侧，PS翻转速率的差异足以产生82%的PS不对称性。这些研究对于钙离子在维持PS不对称性中可能发挥的非酶促作用具有重要意义。
