Song Yujuan, Benison Gregory, Nyarko Afua, Hays Thomas S, Barbar Elisar
Department of Biochemistry and Biophysics, Oregon State University, Corvallis, Oregon 97331, USA.
J Biol Chem. 2007 Jun 8;282(23):17272-9. doi: 10.1074/jbc.M610445200. Epub 2007 Apr 11.
The homodimeric light chains LC8 and Tctex-1 are integral parts of the microtubule motor cytoplasmic dynein, as they directly associate with dynein intermediate chain IC and various cellular cargoes. These light chains appear to regulate assembly of the dynein complex by binding to and promoting dimerization of IC. In addition, both LC8 and Tctex-1 play roles in signaling, apoptosis, and neuronal development that are independent of their function in dynein, but it is unclear how these various activities are modulated. Both light chains undergo specific phosphorylation, and here we present biochemical and NMR analyses of phosphomimetic mutants that indicate how phosphorylation may regulate light chain function. For both LC8 and Tctex-1, phosphorylation promotes dissociation from IC while retaining their binding activity with other non-dynein proteins. Although LC8 and Tctex-1 are homologs having a common fold, their reduced affinity for IC upon phosphorylation arises by different mechanisms. In the case of Tctex-1, phosphorylation directly masks the IC binding site at the dimer interface, whereas for LC8, phosphorylation dissociates the dimer and indirectly eliminates the binding site. This modulation of the monomer-dimer equilibrium by phosphorylation provides a novel mechanism for discrimination among LC8 binding partners.
同二聚体轻链LC8和Tctex-1是微管动力蛋白胞质动力蛋白的组成部分，因为它们直接与动力蛋白中间链IC以及各种细胞货物结合。这些轻链似乎通过与IC结合并促进其二聚化来调节动力蛋白复合物的组装。此外，LC8和Tctex-1在信号传导、细胞凋亡和神经元发育中发挥作用，这些作用独立于它们在动力蛋白中的功能，但尚不清楚这些各种活动是如何被调节的。两种轻链都经历特定的磷酸化，在这里我们展示了模拟磷酸化突变体的生化和核磁共振分析，这些分析表明磷酸化可能如何调节轻链功能。对于LC8和Tctex-1，磷酸化促进与IC的解离，同时保留它们与其他非动力蛋白的结合活性。尽管LC8和Tctex-1是具有共同折叠结构的同源物，但它们磷酸化后对IC亲和力的降低是由不同机制引起的。就Tctex-1而言，磷酸化直接掩盖了二聚体界面处的IC结合位点，而对于LC8，磷酸化使二聚体解离并间接消除结合位点。通过磷酸化对单体-二聚体平衡的这种调节为区分LC8结合伙伴提供了一种新机制。
