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J. Biol. Chem., Vol. 282, Issue 23, 17272-17279, June 8, 2007

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Potential Role for Phosphorylation in Differential Regulation of the Assembly of Dynein Light Chains^*

Yujuan Song, Gregory Benison, Afua Nyarko, Thomas S. Hays, and Elisar Barbar¹

From the Department of Biochemistry and Biophysics, Oregon State University, Corvallis, Oregon 97331 and Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, Minnesota 55455

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.

Received for publication, November 9, 2006 , and in revised form, March 2, 2007.

^* This work was supported by National Science Foundation Career Grant MCB-0417181. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed. Tel.: 541-737-4143; Fax: 541-737-0481; E-mail: barbare{at}science.oregonstate.edu.

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