Wakeham Diane E, Chen Chih-Ying, Greene Barrie, Hwang Peter K, Brodsky Frances M
The G. W. Hooper Foundation, Department of Microbiology and Immunology, University of California, San Francisco, CA 94143-0552, USA.
EMBO J. 2003 Oct 1;22(19):4980-90. doi: 10.1093/emboj/cdg511.
The clathrin triskelion self-assembles into a polyhedral coat surrounding membrane vesicles that sort receptor cargo to the endocytic pathway. A triskelion comprises three clathrin heavy chains joined at their C-termini, extending into proximal and distal leg segments ending in a globular N-terminal domain. In the clathrin coat, leg segments entwine into parallel and anti-parallel interactions. Here we define the contributions of segmental interactions to the clathrin assembly reaction and measure the strength of their interactions. Proximal and distal leg segments were found to lack sufficient affinity to form stable homo- or heterodimers under assembly conditions. However, chimeric constructs of proximal or distal leg segments, trimerized by replacement of the clathrin trimerization domain with that of the invariant chain protein, were able to self-assemble in reversible reactions. Thus clathrin assembly occurs because weak leg segment affinities are coordinated through trimerization, sharing a dependence on multiple weak interactions with other biopolymers. Such polymerization is sensitive to small environmental changes and is therefore compatible with cellular regulation of assembly, disassembly and curvature during formation of clathrin-coated vesicles.
网格蛋白三脚复合体可自我组装成围绕膜泡的多面体衣被，这些膜泡将受体货物分拣至内吞途径。一个三脚复合体由三条在其C端相连的网格蛋白重链组成，延伸为近端和远端的腿部片段，末端是一个球状的N端结构域。在网格蛋白衣被中，腿部片段相互缠绕形成平行和反平行的相互作用。在这里，我们确定了片段间相互作用对网格蛋白组装反应的贡献，并测量了它们相互作用的强度。发现在组装条件下，近端和远端腿部片段缺乏足够的亲和力来形成稳定的同二聚体或异二聚体。然而，通过用不变链蛋白的三聚化结构域替换网格蛋白三聚化结构域而三聚化的近端或远端腿部片段的嵌合构建体，能够在可逆反应中自我组装。因此，网格蛋白的组装是因为腿部片段间的弱亲和力通过三聚化得到协调，与其他生物聚合物一样依赖于多个弱相互作用。这种聚合对微小的环境变化敏感，因此与网格蛋白包被小泡形成过程中组装、拆卸和曲率的细胞调节相兼容。
