The lamin B receptor (LBR) is an integral protein of inner nuclear membrane whose nucleoplasmic amino-terminal domain contributes to the attachment of the membrane to chromatin. Here we analyzed the interactions of a recombinant GST protein containing the amino-terminal domain of the protein with in vitro reconstituted nucleosomes and short DNA fragments. Data show that the LBR amino-terminal domain (AT) binds linker DNA but does not interact with the nucleosome core. Titration and competition studies revealed that the interaction between LBR AT and DNA is saturable, of high affinity (K(D) approximately 4 nM), independent of DNA sequence, and enhanced by DNA curvature and supercoiling. In this respect, LBR amino-terminal domain binding to nucleosomes is similar to that of histone H1 and non histone proteins HMG1/2 which both bind preferentially to linker DNA and present a significant affinity for DNA secondary structures.
Interacting selectively and non-covalently with a chromo shadow domain, a protein domain that is distantly related, and found in association with, the chromo domain.
Evidence
1:
Inferred from Physical InteractionBHF-UCL
The HP1 proteins regulate epigenetic gene silencing by promoting and maintaining chromatin condensation. The HP1 chromodomain binds to methylated histone H3. More enigmatic is the chromoshadow domain (CSD), which mediates dimerization, transcription repression, and interaction with multiple nuclear proteins. Here we show that KAP-1, CAF-1 p150, and NIPBL carry a canonical amino acid motif, PxVxL, which binds directly to the CSD with high affinity. We also define a new class of variant PxVxL CSD-binding motifs in Sp100A, LBR, and ATRX. Both canonical and variant motifs recognize a similar surface of the CSD dimer as demonstrated by a panel of CSD mutants. These in vitro binding results were confirmed by the analysis of polypeptides found associated with nuclear HP1 complexes and we provide the first evidence of the NIPBL/delangin protein in human cells, a protein recently implicated in the developmental disorder, Cornelia de Lange syndrome. NIPBL is related to Nipped-B, a factor participating in gene activation by remote enhancers in Drosophila melanogaster. Thus, this spectrum of direct binding partners suggests an expanded role for HP1 as factor participating in promoter-enhancer communication, chromatin remodeling/assembly, and sub-nuclear compartmentalization.
Interacting selectively and non-covalently with lamin; any of a group of intermediate-filament proteins that form the fibrous matrix on the inner surface of the nuclear envelope.
J. Biol. Chem. 269, 11306-11311 (1994)[PubMed:8157662]
We have determined the primary structure of human LBR, an integral protein of the nuclear envelope inner membrane, and examined its interactions with lamin B and DNA. Human LBR is 68% identical to the chicken lamin B receptor and has a basic nucleoplasmic amino-terminal domain of 208 amino acids followed by a hydrophobic domain with eight putative transmembrane segments. The amino-terminal domain contains a Ser-Arg-rich stretch and consensus sites for phosphorylation by protein kinase A and p34cdc2 protein kinase. A fusion protein containing the amino-terminal domain of human LBR is recognized by autoantibodies from patients with primary biliary cirrhosis, and these serum antibodies label the nuclear envelope when examined by immunofluorescence microscopy. The LBR amino-terminal domain precipitates lamin B from nuclear extracts and retards the migration of double-stranded DNA subjected to agarose gel electrophoresis. When immobilized on nitrocellulose, the amino-terminal domain of LBR also associates with DNA, and the stretch between amino acids 71 and 100, which contains the Ser-Arg-rich stretch, is necessary for DNA binding. These results demonstrate that LBR is conserved among vertebrate species and that its nucleoplasmic domain can potentially mediate the interaction of both the nuclear lamina and the chromatin with the inner nuclear membrane.
Interacting selectively and non-covalently with any protein or protein complex (a complex of two or more proteins that may include other nonprotein molecules).
Evidence
1:
Inferred from Physical InteractionUniProtKB
J. Biol. Chem. 271, 14653-14656 (1996)[PubMed:8663349]
At the nuclear envelope in higher eukaryotic cells, the nuclear lamina and the heterochromatin are adjacent to the inner nuclear membrane, and their attachment is presumably mediated by integral membrane proteins. In a yeast two-hybrid screen, the nucleoplasmic domain of lamin B receptor (LBR), an integral protein of the inner nuclear membrane, associated with two human polypeptides homologous to Drosophila HP1, a heterochromatin protein involved in position-effect variegation. LBR fusion proteins bound to HP1 proteins synthesized by in vitro translation and present in cell lysates. Antibodies against LBR also co-immunoprecipitated HP1 proteins from cell extracts. LBR can interact with chromodomain proteins that are highly conserved in eukaryotic species and may function in the attachment of heterochromatin to the inner nuclear membrane in cells.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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