The C‐terminal domain of the transcriptional corepressor CtBP is intrinsically unstructured

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Abstract
C‐terminal binding proteins (CtBPs) are moonlighting proteins involved in nuclear transcriptional corepression and in Golgi membrane tubule fission. Structural information on CtBPs is available for their substrate‐binding domain, responsible for transcriptional repressor recognition/binding, and for the nucleotide‐binding domain, involved in NAD(H)‐binding and dimerization. On the contrary, little is known about the structure of CtBP C‐terminal region (∼90 residues), hosting sites for post‐translational modifications. In the present communication we apply a combined approach based on bioinformatics, nuclear magnetic resonance, circular dichroism spectroscopy, and small‐angle X‐ray scattering, and we show that the CtBP C‐terminal region is intrinsically unstructured in the full‐length CtBP and in constructs lacking the substrate‐ and/or the nucleotide‐binding domains. The flexible nature of this protein region, and its structural transitions, may be instrumental for CtBP recognition and binding to diverse molecular partners.