Structural Diversity in p160/CREB-binding Protein Coactivator Complexes

Abstract

Ligand-induced transcription by nuclear receptors involves the recruitment of p160 coactivators such as steroid receptor coactivator 1 (SRC1), in complex with histone acetyltransferases such as CREB-binding protein (CBP) and p300. Here we describe the solution structure of a complex formed by the SRC1 interaction domain (SID) of CBP and the activation domain (AD1) of SRC1, both of which contain four helical regions (C␣1, C␣2, C␣3, and C␣3 in CBP and S␣1, S␣2, S␣2, and S␣3 in SRC1). A tight four-helix bundle is formed between S␣1, C␣1, C␣2, and C␣3 that is capped by S␣3. In contrast to the structure of the AD1 domain of the related p160 protein ACTR in complex with CBP SID, the sequences forming S␣2 and S␣2 in SRC1 AD1 are not involved in the interface between the two domains but rather serve to position S␣3. Thus, although the CBP SID domain adopts a similar fold in complex with different p160 proteins, the topologies of the AD1 domains are strikingly different, a feature that is likely to contribute to functional specificity of these coactivator complexes.The lysine acetyltransferase CBP 5 interacts with a large number of nuclear proteins, many of which are transcription factors (1, 2). This is achieved through direct or indirect protein-protein interactions that are mediated by distinct structural domains within the CBP protein such as the KIX, CRD, CH1, CH3, bromodomain and SID domains. The protein-binding domains of CBP display partial specificity, having both distinct and overlapping binding partner profiles, which contributes to the phenomena of synergy and cross-talk between transcription factors (1).The recruitment of CBP to target gene promoters/enhancers facilitates acetylation of histone N-terminal tails, leading to chromatin remodeling and enhanced gene expression. This has been demonstrated for nuclear receptors, which activate transcription of their target genes in response to ligand binding (3, 4). Ligand-bound receptors undergo a conformational change that stimulates their interaction with cofactors that contain functional LXXLL motifs, such as the p160 coactivators SRC1, TIF2, and ACTR (5, 6). Studies of steroid-regulated gene promoters have revealed that p160s and HAT proteins are among the first cofactors recruited in response to ligand (7,8). Such temporally ordered recruitment of coactivators to promoters/enhancers is crucial for the sequential chromatin modification and remodeling events preceding transcription (4).The efficacy of nuclear receptor/cofactor interaction is influenced by a number of determinants, including the precise sequence and number of LXXLL motifs, the sequences flanking core motifs, and other distal sequences (9 -11). CBP contains three LXXLL motifs, although they mediate only weak direct interactions with estrogen, androgen, and progesterone receptors (9, 10). Thus, at least in the case of the steroid receptors, efficient recruitment of CBP/p300 and associated factors is achieved indirectly via the p160 proteins (12).A number of studies have shown that recruitment of C...

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

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Conformational selection in the molten globule state of the nuclear coactivator binding domain of CBP

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Role of Intrinsic Protein Disorder in the Function and Interactions of the Transcriptional Coactivators CREB-binding Protein (CBP) and p300

“…Upon binding to its physiological partners, the NCBD folds to form a bundle of three helices that differ in their topological arrangements in complexes with intrinsically disordered targets, such as the p160 nuclear coactivators ACTR (coactivator for thyroid and retinoid receptors) and SRC-1 and the p53 activation domain (18,54,55), and in the complex with the stably folded interferon regulatory factor IRF-3 (56). Detailed NMR and computational studies suggest that in the unbound state, the NCBD is flexible and fluctuates over an ensemble of conformations that includes both the ACTR/SRC-1-bound conformation and the IRF-3-bound conformation (57-61).…”