Ilangovan Udayar, Ding Wei, Zhong Yan, Wilson Christina L, Groppe Jay C, Trbovich James T, Zúñiga Jorge, Demeler Borries, Tang Qian, Gao Guofeng, Mulder Kathleen M, Hinck Andrew P
Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.
J Mol Biol. 2005 Sep 16;352(2):338-54. doi: 10.1016/j.jmb.2005.07.002.
km23 (96 residues, 11 kDa) is the mammalian ortholog of Drosophila roadblock, the founding member of LC7/robl/km23 class of dynein light chains. km23 has been shown to be serine-phosphorylated following TGFbeta receptor activation and to bind the dynein intermediate chain in response to such phosphorylation. Here, we report the three-dimensional solution structure of km23, which is shown to be that of a homodimer, similar to that observed for the heterodimeric complex formed between p14 and MP1, two distantly related members of the MglB/robl superfamily, but distinct from the LC8 and Tctex-1 classes of dynein light chains, which also adopt homodimeric structures. The conserved surface residues of km23, including three serine residues, are located predominantly on a single face of the molecule. Adjacent to this face is a large cleft formed by the incomplete overlap of loops from opposite monomers. As shown by NMR relaxation data collected at two fields, several cleft residues are flexible on the ns-ps and ms-mus timescales. Based on these observations, we propose that the patch of conserved residues on the central face of the molecule corresponds to the site at which km23 binds the dynein intermediate chain and that the flexible cleft formed between the overlap of loops from the two monomers corresponds to the site at which km23 binds other partners, such as the TGFbeta type II receptor or Smad2.
km23（96个氨基酸残基，11 kDa）是果蝇roadblock在哺乳动物中的直系同源物，roadblock是动力蛋白轻链LC7/robl/km23家族的首个成员。研究表明，TGFβ受体激活后km23会发生丝氨酸磷酸化，并在这种磷酸化作用下与动力蛋白中间链结合。在此，我们报道了km23的三维溶液结构，结果显示它是一个同二聚体，类似于在p14和MP1之间形成的异二聚体复合物，p14和MP1是MglB/robl超家族中两个远亲成员，但与同样采用同二聚体结构的动力蛋白轻链LC8和Tctex-1家族不同。km23保守的表面残基，包括三个丝氨酸残基，主要位于分子的一个面上。在这个面的旁边是一个大裂缝，由相对单体的环不完全重叠形成。如在两个磁场下收集的NMR弛豫数据所示，几个裂缝残基在纳秒-皮秒和毫秒-微秒时间尺度上是灵活的。基于这些观察结果，我们提出分子中心面上的保守残基区域对应于km23与动力蛋白中间链结合的位点，而两个单体的环重叠形成的灵活裂缝对应于km23与其他伙伴结合的位点，如TGFβ II型受体或Smad2。
