Castello-Serrano Ivan, Lorent Joseph H, Ippolito Rossana, Levental Kandice R, Levental Ilya
Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, Texas 77030, United States.
J Phys Chem B. 2020 Jul 16;124(28):5930-5939. doi: 10.1021/acs.jpcb.0c03028. Epub 2020 Jun 4.
Eukaryotic membranes can be partitioned into lipid-driven membrane microdomains called lipid rafts, which function to sort lipids and proteins in the plane of the membrane. As protein selectivity underlies all functions of lipid rafts, there has been significant interest in understanding the structural and molecular determinants of raft affinity. Such determinants have been described for lipids and single-spanning transmembrane proteins; however, how multipass transmembrane proteins (TMPs) partition between ordered and disordered phases has not been widely explored. Here we used cell-derived giant plasma membrane vesicles (GPMVs) to systematically measure multipass TMP partitioning to ordered membrane domains. Across a set of 24 structurally and functionally diverse multipass TMPs, the large majority (92%) had minimal raft affinity. The only exceptions were two myelin-associated four-pass TMPs, myelin and lymphocyte protein (MAL), and proteo lipid protein (PLP). We characterized the potential mechanisms for their exceptional raft affinity and observed that PLP requires cholesterol and sphingolipids for optimal association with ordered membrane domains and that PLP and MAL appear to compete for cholesterol-mediated raft affinity. These observations suggest broad conclusions about the composition of ordered membrane domains in cells and point to previously unrecognized drivers of raft affinity for multipass transmembrane proteins.
真核细胞膜可被划分为称为脂筏的脂质驱动膜微区，其功能是在膜平面内对脂质和蛋白质进行分选。由于蛋白质选择性是脂筏所有功能的基础，人们对理解脂筏亲和力的结构和分子决定因素有着浓厚兴趣。脂质和单跨膜蛋白的此类决定因素已被描述；然而，多跨膜蛋白（TMPs）如何在有序和无序相之间分配尚未得到广泛探索。在这里，我们使用细胞衍生的巨大质膜囊泡（GPMV）系统地测量多跨TMPs向有序膜结构域的分配。在一组24种结构和功能各异的多跨TMPs中，绝大多数（92%）具有最小的脂筏亲和力。唯一的例外是两种髓磷脂相关的四跨TMPs，髓磷脂和淋巴细胞蛋白（MAL）以及蛋白脂蛋白（PLP）。我们表征了它们异常脂筏亲和力的潜在机制，并观察到PLP需要胆固醇和鞘脂才能与有序膜结构域实现最佳结合，并且PLP和MAL似乎竞争胆固醇介导的脂筏亲和力。这些观察结果对细胞中有序膜结构域的组成提出了广泛结论，并指出了此前未被认识到的多跨膜蛋白脂筏亲和力驱动因素。
