title: Structure of a construct of a human poly(C)-binding protein containing the first and second KH domains reveals insights into its regulatory mechanisms.
abstract: Poly(C)-binding proteins (PCBPs) are important regulatory proteins that contain three KH (hnRNP K homology) domains. Binding poly(C) D/RNA sequences via KH domains is essential for multiple PCBP functions. To reveal the basis for PCBP-D/RNA interactions and function, we determined the structure of a construct containing the first two domains (KH1-KH2) of human PCBP2 by NMR. KH1 and KH2 form an intramolecular pseudodimer. The large hydrophobic dimerization surface of each KH domain is on the side opposite the D/RNA binding interface. Chemical shift mapping indicates both domains bind poly(C) DNA motifs without disrupting the KH1-KH2 interaction. Spectral comparison of KH1-KH2, KH3, and full-length PCBP2 constructs suggests that the KH1-KH2 pseudodimer forms, but KH3 does not interact with other parts of the protein. From NMR studies and modeling, we propose possible modes of cooperative binding tandem poly(C) motifs by the KH domains. D/RNA binding may induce pseudodimer dissociation or stabilize dissociated KH1 and KH2, making protein interaction surfaces available to PCBP-binding partners. This conformational change may represent a regulatory mechanism linking D/RNA binding to PCBP functions.
authors.affiliation: Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143, USA.
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Du
authors.forename: Sebastian
authors.initials: S
authors.lastname: Fenn
authors.forename: Richard
authors.initials: R
authors.lastname: Tjhen
authors.forename: Thomas L
authors.initials: TL
authors.lastname: James
mesh_terms: D000595:Amino Acid Sequence; D004247:DNA / Q000737:chemistry; D019281:Dimerization; D005786:Gene Expression Regulation; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016601:RNA-Binding Proteins / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: C501903:PCBP2 protein, human; D016601:RNA-Binding Proteins; D004247:DNA