Distinct conformational states of nuclear receptor–bound CRSP–Med complexes

Abstract

The human CRSP-Med coactivator complex is targeted by a diverse array of sequence-specific regulatory proteins. Using EM and single-particle reconstruction techniques, we recently completed a structural analysis of CRSP-Med bound to VP16 and SREBP-1a. Notably, these activators induced distinct conformational states upon binding the coactivator. Ostensibly, these different conformational states result from VP16 and SREBP-1a targeting distinct subunits in the CRSP-Med complex. To test this, we conducted a structural analysis of CRSP-Med bound to either thyroid hormone receptor (TR) or vitamin D receptor (VDR), both of which interact with the same subunit (Med220) of CRSP-Med. Structural comparison of TR- and VDR-bound complexes (at a resolution of 29 A) indeed reveals a shared conformational feature that is distinct from other known CRSP- Med structures. Importantly, this nuclear receptor-induced structural shift seems largely dependent on the movement of Med220 within the complex.

A Conserved Mediator Hinge Revealed in the Structure of the MED7·MED21 (Med7·Srb7) Heterodimer

“…Strong structural changes have also been observed in the mammalian Mediator coactivators CRSP and ARC upon binding of activator proteins (22,38). In addition to the MED6 hinge, the intrinsic flexibility of the MED7⅐MED21 heterodimer may account for these conformational changes.…”

Transcriptional Regulation inSaccharomyces cerevisiae: Transcription Factor Regulation and Function, Mechanisms of Initiation, and Roles of Activators and Coactivators

“…The best evidence for this comes from mammalian systems, where activators binding to Mediator caused dramatic activator-specific changes in Mediator structure (Taatjes et al 2002(Taatjes et al , 2004Meyer et al 2010). It is not yet proven that these conformational changes occur in functional transcription complexes, but once the mechanisms of these changes are understood, it should be possible to genetically manipulate Mediator conformation and test whether and how it contributes to activation.…”

The Mediator Complex in Plants: Structure, Phylogeny, and Expression Profiling of Representative Genes in a Dicot (Arabidopsis) and a Monocot (Rice) during Reproduction and Abiotic Stress

“…The kinase module phosphorylates subunits of the general transcription factor (GTF) TFIID and Med2 (Hallberg et al, 2004;Liu et al, 2004) and facilitates reinitiation of the preinitiation complex (Yudkovsky et al, 2000). The Med complex has the flexibility to acquire different structures upon binding of different activators to different/same subunits (Taatjes et al, 2002(Taatjes et al, , 2004. These distinct activator-Med structures differentially affect Pol II activity (Meyer et al, 2010) and regulate Med function in genespecific ways .…”