title: Structural transitions of the RING1B C-terminal region upon binding the polycomb cbox domain.
abstract: Polycomb group (PcG) proteins are required for maintaining cell identity and stem cell self-renewal. RING1B and Polycomb (Pc) are two components of a multiprotein complex called polycomb repression complex 1 (PRC1) that is essential for establishing and maintaining long-term repressed gene states. Here we characterize the interaction between the C-terminal region of RING1B (C-RING1B) and the Pc cbox domain. The C-RING1B-cbox interaction displays a 1:1 stoichiometry with dissociation constants ranging from 9.2 to 180 nM for the different Pc orthologues. NMR analysis of C-RING1B alone reveals line broadening. However, when it is in complex with the cbox domain, there is a striking change to the NMR spectrum indicative of conformational tightening. This conformational change may arise from the organization of the C-RING1B subdomains. The C-terminal regions of all PcG RING1 proteins are composed of two stretches of conserved sequences separated by a variable linker sequence. While the entire C-RING1B region is required for cbox binding, the N- and C-terminal halves of C-RING1B can be separated and are able to interact, suggesting the presence of an intramolecular interaction within C-RING1B. The flexibility within the C-RING1B structure allowing transitions between the intramolecular bound and unbound states may cause the broadened peaks of the C-RING1B NMR spectrum. Binding the cbox domain stabilizes C-RING1B, whereby broadening is eliminated. The presence of flexible regions could allow C-RING1B to bind a variety of different factors, ultimately recruiting RING1B and its associated PcG proteins to different genomic loci.
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center at San Antonio, MSC 7760, 7703 Floyd Curl Drive, San Antonio, Texas 78229-3900, USA.
authors.forename: Renjing
authors.initials: R
authors.lastname: Wang
authors.forename: Udayar
authors.initials: U
authors.lastname: Ilangovan
authors.forename: Angela K
authors.initials: AK
authors.lastname: Robinson
authors.forename: Virgil
authors.initials: V
authors.lastname: Schirf
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Schwarz
authors.forename: Eileen M
authors.initials: EM
authors.lastname: Lafer
authors.forename: Borries
authors.initials: B
authors.lastname: Demeler
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Hinck
authors.forename: Chongwoo A
authors.initials: CA
authors.lastname: Kim
mesh_terms: D000595:Amino Acid Sequence; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D008969:Molecular Sequence Data; D063150:Polycomb Repressive Complex 1; D063146:Polycomb-Group Proteins; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D020349:Surface Plasmon Resonance; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014461:Ultracentrifugation
chemical_list: D004268:DNA-Binding Proteins; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins; D063150:Polycomb Repressive Complex 1; C489841:RNF2 protein, human; D044767:Ubiquitin-Protein Ligases