Structure and Functional Relationship of Band 3 Protein

我们最近对带3蛋白（一种典型的多跨多位膜蛋白）的研究表明，一些疏水肽部分不含边界脂质，尽管它们的疏水性与结合的蛋白相当（Hamasaki, et al.， J. Biochem. 122, 577-585(1997)）。此外，band 3蛋白的预期跨膜肽部分彼此不相等，其中一些没有拓扑信号活性（Ota等，Biol.）。化学，273,28286-28291(1998))。研究还发现，在体外生物合成过程中，拓扑信号活性受到跨膜肽部分相互肽-肽相互作用的影响（Ota, et al., Biol.）。化学，273,28286-28291(1998))。有趣的是，我们还观察到一种共翻译插入模式的证据，其中内部信号-另一个具有Nexo/Ccyt拓扑结构的序列将跨膜配置到先前的亲水性肽段上（Ota等人，Molecular cell . More 2, 495-503(1998)）。提示亲水性肽部分可以穿过被其他跨膜肽部分包围的膜脂双分子层（尤其是两亲性跨膜肽部分）。我们很有可能推测，在蛋白质生物合成和质膜交叉事件的整个过程中，多跨多位膜蛋白的相互肽-肽相互作用都发生了(Hamasaki, et al., Biochem。细胞。生物学报，76,729-733(1998))。基于这些证据，可以得出结论，疏水跨膜肽部分不一定与膜脂双层中的边界脂结合。因此，疏水性并不是多跨膜蛋白形成跨膜段的绝对条件。第2类部分(见J. Biochem. 122, 577-585 (1997)；物化学。细胞生物学，79,729-733(1998))在膜脂双分子层中有相当大的自由度。含有第2类部分的蛋白质比仅由与边界脂结合的跨膜肽部分组成的膜蛋白具有更灵活的结构。这些柔性区域在膜脂双分子层内底物-肽相互作用或配体介导的构象变化中发挥重要作用。对其他多聚膜蛋白的进一步研究将支持这一新概念。少

Our recent studies on band 3 protein, a typical multi-spanning polytopic membrane protein, implied that some hydrophobicpeptideportions were found as free from boundary lipids even though their hydrophobicity was comparable to that of bound from (Hamasaki, et al., J. Biochem. 122, 577-585(1997)). Moreover, the anticipated transmembrane peptide portions of band 3 protein were not equivalent to each other and some of them had no topogenic signal activities (Ota, et al., Biol. Chem. 273, 28286-28291(1998)). It was also found that topogenic signal activities were affected by the mutual peptide-peptide interactions of the transmembrane peptide portions during biosynthesis in vitro (Ota, et al., Biol. Chem. 273, 28286-28291(1998)). Intriguingly, we also observed the evidence for a mode of co-translational insertion in which an internal signal-another sequence with Nexo/Ccyt topology conferred a transmembrane disposition onto a preceding hydrophilic peptide segment (Ota, et al., Molecular Cel … More l 2, 495-503(1998)), suggesting that hydrophilic peptide portions can transverse the membrane lipid bilayer surrounded by other trasnmembrane peptide portions (especially with amphipathic transmembrane peptide portions). It is highly probable to speculated that the mutual peptide-peptide interactions of multi-spanning polytopic membrane proteins occurred throughout the protein biosynthesis and plasma membrane intersection events (Hamasaki, et al., Biochem. Cell., Biol. 76, 729-733(1998)).Based on this evidence, it can be concluded that the hydrophobic transmembrane peptide portions are not necessarily bound with boundary lipids in the membrane lipid bilayer. Thus, hydrophobicity is not an absolute requirement for the formation of a transmembrane segment in multispanning polytopic membrane proteins. Category 2 portions (see J. Biochem. 122, 577-585 (1997) ; Biochem. Cell Biol. 79, 729-733 (1998)) have considerable freedom in the membrane lipid bilayer. Proteins containing category 2 portions have a more flexible structure than membrane proteins that consist only of transmembrane peptide portions bound with boundary lipids. These flexible regions must play important roles in substrate-peptide interactions or ligand-mediated conformational change within membrane lipid bilayers. Further study on other polytopic membrane proteins would support this new concept. Less