A fundamental feature of cellular plasma membranes (PMs) is an asymmetric lipid distribution between the bilayer leaflets. However, neither the detailed, comprehensive compositions of individual PM leaflets nor how these contribute to structural membrane asymmetries have been defined. We report the distinct lipidomes and biophysical properties of both monolayers in living mammalian PMs. Phospholipid unsaturation is dramatically asymmetric, with the cytoplasmic leaflet being approximately twofold more unsaturated than the exoplasmic leaflet. Atomistic simulations and spectroscopy of leaflet-selective fluorescent probes reveal that the outer PM leaflet is more packed and less diffusive than the inner leaflet, with this biophysical asymmetry maintained in the endocytic system. The structural asymmetry of the PM is reflected in the asymmetric structures of protein transmembrane domains. These structural asymmetries are conserved throughout Eukaryota, suggesting fundamental cellular design principles.

中文翻译：

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质膜在脂质不饱和度、堆积和蛋白质形状方面是不对称的。

细胞质膜 (PM) 的一个基本特征是双层小叶之间的不对称脂质分布。然而，尚未定义单个 PM 传单的详细、全面的组成，以及它们如何导致结构膜不对称。我们报告了活哺乳动物 PM 中两个单层的独特脂质组和生物物理特性。磷脂不饱和度显着不对称，细胞质小叶的不饱和度大约是外质小叶的两倍。小叶选择性荧光探针的原子模拟和光谱显示，外部 PM 小叶比内部小叶更密集且扩散性更小，并且在内吞系统中保持这种生物物理不对称性。PM的结构不对称反映在蛋白质跨膜域的不对称结构上。这些结构不对称在整个真核生物中都是保守的，这表明了基本的细胞设计原则。