Recognition of pre-formed and flexible elements of an RNA stem-loop by nucleolin.

Nucleolin is an abundant nucleolar protein which is essential for ribosome biogenesis. The first two of its four tandem RNA-binding domains (RBD12) specifically recognize a stem-loop structure containing a conserved UCCCGA sequence in the loop called the nucleolin-recognition element (NRE). We have determined the structure of the consensus SELEX NRE (sNRE) by NMR spectroscopy.

Delineation of the calcineurin-interacting region of cyclophilin B.

The immunosuppressant drug cyclosporin A (CsA) inhibits T-cell function by blocking the phosphatase activity of calcineurin. This effect is mediated by formation of a complex between the drug and cyclophilin (CyP), which creates a composite surface able to make high-affinity contacts with calcineurin. In vitro, the CyPB/CsA complex is more effective in inhibiting calcineurin than the CyPA/CsA and CyPC/CsA complexes, pointing to fine structural differences in the calcineurin-binding region.

Molecular basis of sequence-specific recognition of pre-ribosomal RNA by nucleolin.

The structure of the 28 kDa complex of the first two RNA binding domains (RBDs) of nucleolin (RBD12) with an RNA stem-loop that includes the nucleolin recognition element UCCCGA in the loop was determined by NMR spectroscopy. The structure of nucleolin RBD12 with the nucleolin recognition element (NRE) reveals that the two RBDs bind on opposite sides of the RNA loop, forming a molecular clamp that brings the 5' and 3' ends of the recognition sequence close together and stabilizing the stem-loop. The specific interactions observed in the structure explain the sequence specificity for the NRE sequence.

Solution structure of the two N-terminal RNA-binding domains of nucleolin and NMR study of the interaction with its RNA target.

Nucleolin is an abundant 70 kDa nucleolar protein involved in many aspects of ribosomal RNA biogenesis. The central region of nucleolin contains four tandem consensus RNA-binding domains (RBD). The two most N-terminal domains (RBD12) bind with nanomolar affinity to an RNA stem-loop containing the consensus sequence UCCCGA in the loop.

Determination of metal ion binding sites within the hairpin ribozyme domains by NMR.

Cations play an important role in RNA folding and stabilization. The hairpin ribozyme is a small catalytic RNA consisting of two domains, A and B, which interact in the transition state in an ion-dependent fashion. Here we describe the interaction of mono-, di-, and trivalent cations with the domains of the ribozyme, as studied by homo- and heteronuclear NMR spectroscopy.

Cyclophilin B binding to platelets supports calcium-dependent adhesion to collagen.

We have recently reported that cyclophilin B (CyPB), a secreted cyclosporine-binding protein, could bind to T lymphocytes through interactions with two types of binding sites. The first ones, referred to as type I, involve interactions with the conserved domain of CyPB and promote the endocytosis of surface-bound ligand, while the second type of binding sites, termed type II, are represented by glycosaminoglycans (GAG). Here, we further investigated the interactions of CyPB with blood cell populations.

Receptor-mediated transcytosis of cyclophilin B through the blood-brain barrier.

Cyclophilin B (CyPB) is a cyclosporin A (CsA)-binding protein mainly located in intracellular vesicles and secreted in biological fluids. In previous works, we demonstrated that CyPB interacts with T lymphocytes and enhances in vitro cellular incorporation and activity of CsA. In addition to its immunosuppressive activity, CsA is able to promote regeneration of damaged peripheral nerves.

Solution structure of the HMG protein NHP6A and its interaction with DNA reveals the structural determinants for non-sequence-specific binding.

NHP6A is a chromatin-associated protein from Saccharomyces cerevisiae belonging to the HMG1/2 family of non-specific DNA binding proteins. NHP6A has only one HMG DNA binding domain and forms relatively stable complexes with DNA. We have determined the solution structure of NHP6A and constructed an NMR-based model structure of the DNA complex.

Two distinct regions of cyclophilin B are involved in the recognition of a functional receptor and of glycosaminoglycans on T lymphocytes.

Cyclophilin B is a cyclosporin A-binding protein exhibiting peptidyl-prolyl cis/trans isomerase activity. We have previously shown that it interacts with two types of binding sites on T lymphocytes. The type I sites correspond to specific functional receptors and the type II sites to sulfated glycosaminoglycans.

Solution structure of the loop B domain from the hairpin ribozyme.

The hairpin ribozyme is a small catalytic RNA with a unique two-domain structure. Here we present the solution structure of the loop B domain of the hairpin ribozyme, which contains most of the catalytically essential nucleotides. The 38-nucleotide domain contains a 16-nucleotide internal loop that forms one of the largest non-Watson-Crick segments of base pairing thus far determined by either NMR or crystallography.

Involvement of two classes of binding sites in the interactions of cyclophilin B with peripheral blood T-lymphocytes.

Cyclophilin B (CyPB) is a cyclosporin A (CsA)-binding protein, mainly associated with the secretory pathway, and is released in biological fluids. We recently reported that CyPB specifically binds to T-lymphocytes and promotes enhanced incorporation of CsA. The interactions with cellular binding sites involved, at least in part, the specific N-terminal extension of the protein.

Enhancing the effect of secreted cyclophilin B on immunosuppressive activity of cyclosporine.

Background: Cyclophilin B (CyPB) is a cyclosporine (CsA)-binding protein, located within intracellular vesicles and secreted in biological fluids. In previous works, we reported that CyPB specifically interacts with the T-cell membrane and potentiates the ability of CsA to inhibit CD3-induced proliferation of T lymphocytes.

Methods: CyPB levels were measured in plasma from healthy donors and transplant patients.

Determination of the NMR structure of the complex between U1A protein and its RNA polyadenylation inhibition element.

RNA-protein recognition is critical to post-transcriptional regulation of gene expression, yet poorly understood at the molecular level. The relatively slow progress in understanding this important area of molecular biology is due to difficulties in obtaining good-quality crystals and derivatives, and in preparing samples suitable for NMR investigation. The determination of the structure of the complex between the human U1A protein and its polyadenylation inhibition element is described here.

Structural basis of the RNA-binding specificity of human U1A protein.

The RNP domain is a very common eukaryotic protein domain involved in recognition of a wide range of RNA structures and sequences. Two structures of human U1A in complex with distinct RNA substrates have revealed important aspects of RNP-RNA recognition, but have also raised intriguing questions concerning the origin of binding specificity. The beta-sheet of the domain provides an extensive RNA-binding platform for packing aromatic RNA bases and hydrophobic protein side chains.

Distribution of cyclophilin B-binding sites in the subsets of human peripheral blood lymphocytes.

Cyclophilin B (CyPB) is a cyclosporin A (CsA)-binding protein, mainly associated with the secretory pathway and released in biological fluids. We have recently demonstrated that both free CyPB and CyPB-CsA complex specifically bind to peripheral blood T lymphocytes and are internalized. These results suggest that CyPB might promote the targeting of the drug into sensitive cells.

How accurately and precisely can RNA structure be determined by NMR?

The great diversity of RNA biological functions has led to widespread interest in RNA structure. Advances in synthetic and spectroscopic techniques have recently allowed the extension of NMR methods of structure determination to RNA structures of significant size and increased biological significance. However, it has not yet been established how accurately and precisely RNA structure can be determined by NMR.

Involvement of the N-terminal part of cyclophilin B in the interaction with specific Jurkat T-cell binding sites.

Cyclophilin B (CyPB) is secreted in biological fluids such as blood or milk and binds to a specific receptor present on the human lymphoblastic cell line Jurkat and on human peripheral blood lymphocytes. This study was intended to specify the areas of CyPB that are involved in the interaction with the receptor. A synthetic peptide corresponding to the first 24 N-terminal amino acid residues of CyPB was shown to specifically recognize the receptor.

Cyclophilin B mediates cyclosporin A incorporation in human blood T-lymphocytes through the specific binding of complexed drug to the cell surface.

Cyclophilin B (CyPB) is a cyclosporin A (CsA)-binding protein located within intracellular vesicles and released in biological fluids. We recently reported the specific binding of this protein to T-cell surface receptor which is internalized even in the presence of CsA. These results suggest that CyPB might target the drug to lymphocytes and consequently modify its activity.

Specificity of ribonucleoprotein interaction determined by RNA folding during complex formulation.

Many proteins involved in pre-mRNA processing contain one or more copies of a 70-90-amino-acid alphabeta module called the ribonucleoprotein domain. RNA maturation depends on the specific recognition by ribonucleoproteins of RNA elements within pre-mRNAs and small nuclear RNAs. The human U1A protein binds an RNA hairpin during splicing, and regulates its own expression by binding an internal loop in the 3'-untranslated region of its pre-mRNA, preventing polyadenylation.

Solution structure of the N-terminal RNP domain of U1A protein: the role of C-terminal residues in structure stability and RNA binding.

The solution structure of a fragment of the human U1A spliceosomal protein containing residues 2 to 117 (U1A117) determined using multi-dimensional heteronuclear NMR is presented. The C-terminal region of the molecule is considerably more ordered in the free protein than thought previously and its conformation is different from that seen in the crystal structure of the complex with U1 RNA hairpin II. The residues between Asp90 and Lys98 form an alpha-helix that lies across the beta-sheet, with residues IIe93, IIe94 and Met97 making contacts with Leu44, Phe56 and IIe58.

Evidence that human milk isolated cyclophilin B corresponds to a truncated form.

Cyclophilin B (CyPB) is a member of the cyclophilin family (cyclosporin A-binding proteins) with specific N- and C-terminal extensions. In contrast to cyclophilin A, CyPB owns a signal sequence leading to its translocation in the endoplasmic reticulum. CyPB was reported to be present in human blood and milk, suggesting it is secreted.

Structure of the P1 helix from group I self-splicing introns.

The upstream cleavage site of group I self-splicing introns is identified by an absolutely conserved U.G base-pair within a double helix. Mutant introns with a wobble C.

Novel three-dimensional 1H-13C-31P triple resonance experiments for sequential backbone correlations in nucleic acids.

Backbone-driven assignment methods that utilize covalent connectivities have greatly facilitated spectral assignments of proteins. In nucleic acids, 1H-13C-31P correlations could play a similar role, and several related experiments (HCP) have recently been presented for backbone-driven sequential assignments in RNA. The three-dimensional extension of 1H-31P Het-Cor (P,H-COSY-H,C-HMQC) and Het-TOCSY (P,H-TOCSY-H,C-HMQC) experiments presented here complements HCP experiments as tools for spectral assignments and extraction of dihedral angle constraints.

Divalent metal ion binding to a conserved wobble pair defining the upstream site of cleavage of group I self-splicing introns.

The upstream site of cleavage of all group I self-splicing introns is identified by an absolutely conserved U.G base pair. Although a wobble C.

Selective assay for CyPA and CyPB in human blood using highly specific anti-peptide antibodies.

Cyclophilins A and B (CyPA and CyPB) are known to be the main binding proteins for cyclosporin A (CsA), a potent immunosuppressive drug. Due to the high homology between the two proteins, antibodies to CyPB were found to cross-react with CyPA. In order to avoid this phenomenon, we raised specific antibodies against peptides copying the most divergent parts of the two sequences.