Chinmay Y Majmudar

University of Michigan, Ann Arbor, MI, United States

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Publications (13)95.39 Total impact

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    ABSTRACT: Like many coactivators, the GACKIX domain of the master coactivator CBP/p300 recognizes transcriptional activators of diverse sequence composition via dynamic binding surfaces. The conformational dynamics of GACKIX that underlie its function also render it especially challenging for structural characterization. We find that the ligand discovery strategy of Tethering is an effective method for identifying small molecule fragments that stabilize the GACKIX domain and enables, for the first time, the crystallographic characterization of this important motif. The 2.0 Å resolution structure of GACKIX complexed to a small molecule was further analyzed by molecular dynamics simulations, revealing the importance of specific side chain motions that remodel the activator binding site in order to accommodate binding partners of distinct sequence and size. More broadly, these results suggest that Tethering can be a powerful strategy for identifying small molecule stabilizers of conformationally malleable proteins, thus facilitating their structural characterization and accelerating the discovery of small molecule modulators.
    Journal of the American Chemical Society 02/2013; · 10.68 Impact Factor
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    ABSTRACT: Capturing a coactivator, naturally: The natural products sekikaic acid and lobaric acid, isolated after a high throughput screen of a structurally diverse extract collection, effectively target the dynamic binding interfaces of the GACKIX domain of the coactivator CBP/p300. These molecules are the most effective inhibitors of the GACKIX domain yet described and are uniquely selective for this domain.
    Angewandte Chemie International Edition 10/2012; · 11.34 Impact Factor
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    ABSTRACT: Currently there are few methods suitable for the discovery and characterization of transient, moderate affinity protein-protein interactions in their native environment, despite their prominent role in a host of cellular functions including protein folding, signal transduction, and transcriptional activation. Here we demonstrate that a genetically encoded photoactivatable amino acid, p-benzoyl-l-phenylalanine, can be used to capture transient and/or low affinity binding partners in an in vivo setting. In this study, we focused on ensnaring the coactivator binding partners of the transcriptional activator VP16 in S. cerevisiae. The interactions between transcriptional activators and coactivators in eukaryotes are moderate in affinity and short-lived, and due in part to these characteristics, identification of the direct binding partners of activators in vivo has met with only limited success. We find through in vivo photo-cross-linking that VP16 contacts the Swi/Snf chromatin-remodeling complex through the ATPase Snf2(BRG1/BRM) and the subunit Snf5 with two distinct regions of the activation domain. An analogous experiment with Gal4 reveals that Snf2 is also a target of this activator. These results suggest that Snf2 may be a valuable target for small molecule probe discovery given the prominent role the Swi/Snf complex family plays in development and in disease. More significantly, the successful implementation of the in vivo cross-linking methodology in this setting demonstrates that it can be applied to the discovery and characterization of a broad range of transient and/or modest affinity protein-protein interactions.
    ACS Chemical Biology 12/2011; 6(12):1321-6. · 5.44 Impact Factor
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    Angewandte Chemie International Edition 09/2009; 48(38):7021-4. · 11.34 Impact Factor
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    ABSTRACT: Protein-protein interactions play an essential role in cellular function, and methods to discover and characterize them in their native context are of paramount importance for gaining a deeper understanding of biological networks. In this study, an enhanced nonsense suppression system was utilized to incorporate the nonnatural amino acid p-benzoyl-L-phenylalanine (pBpa) throughout the transcriptional activation domain of the prototypical eukaryotic transcriptional activator Gal4 in vivo (S. cerevisiae). Functional studies of the pBpa-containing Gal4 mutants suggest that this essential binding interface of Gal4 is minimally impacted by these substitutions, with both transcriptional activity and sensitivity to growth conditions maintained. Further supporting this are in vivo cross-linking studies, including the detection of a key binding partner of Gal4, the inhibitor protein Gal80. Cross-linking with a range of pBpa-containing mutants revealed a Gal4 x Gal80 binding interface that extends beyond that previously predicted by conventional strategies. Thus, this approach can be broadened to the discovery of novel binding partners of transcription factors, information that will be critical for the development of therapeutically useful small molecule modulators of these protein-protein interactions.
    Journal of the American Chemical Society 09/2009; 131(40):14240-2. · 10.68 Impact Factor
  • Chinmay Y Majmudar, Anne E Labut, Anna K Mapp
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    ABSTRACT: There is tremendous interest in developing activator artificial transcription factors that functionally mimic endogenous transcriptional activators for use as mechanistic probes, as components of synthetic cell circuitry, and in transcription-targeted therapies. Here, we demonstrate that a phage display selection against the transcriptional activation domain binding motif of the coactivator Tra1(TRRAP) produces distinct sequences that function with similar binding modes and potency as natural activators. These findings set the stage for binding screens with small molecule libraries against TAD binding motifs to yield next-generation small molecule TADs.
    Bioorganic & medicinal chemistry letters 06/2009; 19(14):3733-5. · 2.65 Impact Factor
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    ABSTRACT: Small molecules that reconstitute the binding mode(s) of a protein and in doing so elicit a programmed functional response offer considerable advantages in the control of complex biological processes. The development challenges of such molecules are significant, however. Many protein-protein interactions require multiple points of contact over relatively large surface areas. More significantly, several binding modes can be superimposed upon a single sequence within a protein, and a true small molecule replacement must be preprogrammed for such multimodal binding. This is the case for the transcriptional activation domain or TAD of transcriptional activators as these motifs utilize a poorly characterized multipartner binding profile in order to stimulate gene expression. Here we describe a unique class of small molecules that exhibit both function and a binding profile analogous to natural transcriptional activation domains. Of particular note, the small molecules are the first reported to bind to the KIX domain within the CREB binding protein (CBP) at a site that is utilized by natural activators. Further, a comparison of functional and nonfunctional small molecules indicates that an interaction with CBP is a key contributor to transcriptional activity. Taken together, the evidence suggests that the small molecule TADs mimic both the function and mechanism of their natural counterparts and thus present a framework for the broader development of small molecule transcriptional switches.
    ACS Chemical Biology 05/2009; 4(5):335-44. · 5.44 Impact Factor
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    ABSTRACT: A persistent problem in heterologous protein production is insolubility of the target protein when expressed to high level in the host cell. A widely employed strategy for overcoming this problem is the use of fusion tags. The best fusion tags promote solubility, may function as purification handles and either do not interfere with downstream applications or may be removed from the passenger protein preparation. A novel fusion tag is identified that meets these criteria. This fusion tag is a monomeric mutant of the Ocr protein (0.3 gene product) of bacteriophage T7. This fusion tag displays solubilizing activity with a variety of different passenger proteins. We show that it may be used as a purification handle similar to other fusion tags. Its small size and compact structure are compatible with its use in downstream applications of the passenger protein or it may be removed and purified away from the passenger protein. The use of monomeric Ocr (Mocr) as a complement to other fusion tags such as maltose-binding protein will provide greater flexibility in protein production and processing for a wide variety of protein applications.
    Protein Expression and Purification 10/2008; 63(1):40-9. · 1.43 Impact Factor
  • Jenifer K Lum, Chinmay Y Majmudar, Aseem Z Ansari, Anna K Mapp
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    ABSTRACT: Significant efforts have been devoted to the development of artificial transcriptional activators for use as mechanistic tools, as therapeutic agents, and for biomanufacturing applications. One of the primary challenges has been the development of artificial activators that exhibit potency in cells comparable to that of endogenous activators; the vast majority function only moderately in the cellular context. Here we demonstrate that the superimposition of two distinct binding modes, a masking interaction and an interaction with the transcriptional machinery, has a profoundly positive effect on the cellular activity of artificial activators, with up to 600-fold enhancement observed. Incorporation of this feature into future generations of small molecule transcriptional activators should increase their nuclear uptake and facilitate their accessibility to their target proteins, thus significantly augmenting both their activity and utility.
    ACS Chemical Biology 12/2006; 1(10):639-43. · 5.44 Impact Factor
  • Chinmay Y Majmudar, Anna K Mapp
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    ABSTRACT: Given the correlation between many human diseases and mis-regulated transcription, there is a growing need for molecules that can inhibit or mimic key interactions between transcriptional activators and their binding partners. Because transcriptional activators typically participate in many different protein-protein binding events, the identification of small molecules or peptides that specifically target individual interactions represents a significant challenge. In spite of this, several small molecules that preferentially inhibit particular complexes of transcriptional activators or mimic the function of activators have recently been reported. These molecules serve as excellent mechanistic tools for studying transcription and, further, have outstanding therapeutic potential.
    Current Opinion in Chemical Biology 11/2005; 9(5):467-74. · 9.47 Impact Factor
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    ABSTRACT: Despite their enormous potential as novel research tools and therapeutic agents, artificial transcription factors (ATFs) that up-regulate transcription robustly in vivo remain elusive. In investigating an ATF that does function exceptionally well in vivo, we uncovered an unexpected relationship between transcription function and a binding interaction between the activation domain and an adjacent region of the DNA binding domain. Disruption of this interaction leads to complete loss of function in vivo, even though the activation domain is still able to bind to its target in the transcriptional machinery. We propose that this interaction parallels those between natural activation domains and their regulatory proteins, concealing the activation domain from solvent and the cellular milieu until it binds to its transcriptional machinery target. Inclusion of this property in the future design of ATFs should enhance their efficacy in vivo.
    Journal of Biological Chemistry 09/2005; 280(33):29689-98. · 4.65 Impact Factor
  • Chinmay Y Majmudar, Jenifer K Lum, Lev Prasov, Anna K Mapp
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    ABSTRACT: Misregulated transcription is linked to many human diseases, and thus artificial transcriptional activators are highly desirable as mechanistic tools and as replacements for their malfunctioning natural counterparts. We previously reported two artificial transcriptional activation domains obtained from synthetic peptide libraries screened for binding to the yeast transcription protein Med15(Gal11). Here we demonstrate that the transcriptional potency of the Med15 ligands is increased through straightforward structural alterations. These artificial activation domains upregulate transcription via specific Med15 binding interactions and do not function in mammalian cells, which lack Med15. This functional specificity stands in contrast to most natural or artificial activation domains that function across all eukaryotic cell types. The results indicate that the screening strategy holds excellent promise for identifying peptide and small molecule transcriptional activators that function by unique mechanisms with advantageous specificity properties.
    Chemistry & Biology 04/2005; 12(3):313-21. · 6.16 Impact Factor
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    ABSTRACT: The link between a growing number of human diseases and misregulation of gene expression has spurred intense interest in artificial transcriptional activators that could be used to restore controlled expression of affected genes. To expand the repertoire of activation domains available for the construction of artificial transcriptional regulators, a selection strategy was used to identify two unique activation domain motifs. These activation domains bear little sequence homology to endogenous counterparts and bind to unique sites within the transcriptional machinery. A comparison with two well-characterized activation domains, VP2 and P201, demonstrated for the first time that functional potency is not solely dictated by binding affinity. Finally, the selection strategy described is readily applicable to the identification of small molecule activation domains.
    Journal of the American Chemical Society 11/2003; 125(41):12390-1. · 10.68 Impact Factor