Liu Dongmei, Novick Peter
Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92130.
Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92130
J Cell Biol. 2014 Oct 13;207(1):59-72. doi: 10.1083/jcb.201404122.
The exocyst serves to tether secretory vesicles to cortical sites specified by polarity determinants, in preparation for fusion with the plasma membrane. Although most exocyst components are brought to these sites by riding on secretory vesicles as they are actively transported along actin cables, Exo70p displays actin-independent localization to these sites, implying an interaction with a polarity determinant. Here we show that Exo70p directly and specifically binds to the polarity determinant scaffold protein Bem1p. The interaction involves multiple domains of both Exo70p and Bem1p. Mutations in Exo70p that disrupt its interaction with Bem1, without impairing its interactions with other known binding partners, lead to the loss of actin-independent localization. Synthetic genetic interactions confirm the importance of the Exo70p-Bem1p interaction, although there is some possible redundancy with Sec3p and Sec15p, other exocyst components that also interact with polarity determinants. Similar to Sec3p, the actin-independent localization of Exo70p requires a synergistic interaction with the phosphoinositide PI(4,5)P2.
外排体复合物用于将分泌小泡拴系到由极性决定因子指定的皮质位点，为与质膜融合做准备。尽管大多数外排体复合物成分是在分泌小泡沿着肌动蛋白丝主动运输时搭便车被带到这些位点的，但Exo70p在这些位点呈现出不依赖肌动蛋白的定位，这意味着它与一个极性决定因子存在相互作用。在此我们表明，Exo70p直接且特异性地与极性决定因子支架蛋白Bem1p结合。这种相互作用涉及Exo70p和Bem1p的多个结构域。Exo70p中破坏其与Bem1p相互作用但不损害其与其他已知结合伴侣相互作用的突变，会导致不依赖肌动蛋白的定位丧失。合成遗传相互作用证实了Exo70p - Bem1p相互作用的重要性，尽管与Sec3p和Sec15p（其他也与极性决定因子相互作用的外排体复合物成分）可能存在一些冗余。与Sec3p类似，Exo70p不依赖肌动蛋白的定位需要与磷脂酰肌醇PI(4,5)P2发生协同相互作用。
