CUO-Recherche, Hôpital du Saint-Sacrement, Centre de recherche du CHU de Québec and Département d'ophtalmologie, Faculté de médecine, Université Laval, Québec, Québec, G3K 1A3, Canada.
Institut Europeen de Chimie et de Biologie, UMR 5248 Chimie et Biologie des Membranes et des Nanoobjets, CNRS-Université de Bordeaux 1, Pessac, France.
Colloids Surf B Biointerfaces. 2019 Feb 1;174:291-299. doi: 10.1016/j.colsurfb.2018.11.017. Epub 2018 Nov 12.
Neurocalcin delta (NCALD) is a member of the neuronal calcium sensors protein family. In the retina, NCALD is expressed by ganglion and amacrine cells. NCALD is composed of 4 EF-hand motifs but only 3 of them may bind calcium. The binding of calcium induces a conformational change of the protein which leads to the extrusion of its N-terminal myristoyl group as well as some hydrophilic residues. This mechanism, named calcium-myristoyl switch, is presumably involved in its membrane binding. The parameters responsible for the interaction of NCALD with membranes are only partially known. The purpose of this study was thus to gather more information on the membrane binding behavior of NCALD using lipid monolayers, including the influence of the lipid composition, the calcium and the myristoyl group. NCALD was injected underneath different lipid monolayers and this model membrane allowed the determination of the binding parameters as maximum insertion pressure (MIP) and synergy. The values of MIP are larger when monolayers were composed of a saturated phospholipid with phosphoethanolamine polar head. This trend is confirmed by polarization modulation infrared reflection absorption spectroscopy measurements. Moreover, the observations by fluorescence microscopy show that NCALD preferentially interacts with phospholipids which are in the liquid-condensed physical state, as found in membrane microdomains. This observation could explain the changes of NCALD expression level in the brains of patients suffering from Alzheimer's disease because of the alteration of lipid composition in microdomains structures.
神经钙调蛋白 δ（NCALD）是神经元钙传感器蛋白家族的成员。在视网膜中，NCALD 由节细胞和无长突细胞表达。NCALD 由 4 个 EF 手基序组成，但只有 3 个可以结合钙。钙的结合诱导蛋白质构象发生变化，导致其 N 端豆蔻酰基团和一些亲水残基的挤出。这种机制被称为钙-豆蔻酰开关，可能参与其膜结合。NCALD 与膜相互作用的参数仅部分已知。因此，本研究的目的是使用脂质单层收集有关 NCALD 膜结合行为的更多信息，包括脂质组成、钙和豆蔻酰基的影响。将 NCALD 注入不同的脂质单层下，这种模型膜允许确定结合参数，如最大插入压力（MIP）和协同作用。当单层由具有磷酸乙醇胺极性头的饱和磷脂组成时，MIP 的值更大。偏振调制红外反射吸收光谱测量证实了这一趋势。此外，荧光显微镜观察表明，NCALD 优先与处于液态凝聚物理状态的磷脂相互作用，如在膜微区中发现的那样。这种观察结果可以解释阿尔茨海默病患者大脑中 NCALD 表达水平的变化，因为微区结构中脂质组成的改变。
