Immunoglobulin heavy chain binding protein

Pre-B lymphocytes, and hybridomas derived from them, synthesize immunoglobulin heavy (IgH) chain in the absence of light (L) chain. In the Abelson virus transformed line 18-81, which is representative of the pre-B cell stage, we observed that at least some of the H-chains are bound to a protein other than L-chain. Here we show that the protein (which we term immunoglobulin heavy-chain binding protein, BiP) binds non-covalently to free IgH, but not to IgH associated with IgL.     

香叶木苷的血浆蛋白结合率研究

研究香叶木苷的血浆蛋白结合率．以体外方式，用平衡透析法模拟香叶木苷在大鼠体内与血浆蛋白结合的过程，并以高效液相色谱法测定香叶木苷在透析袋内血浆中的药物质量浓度与透析袋外缓冲液中的质量浓度，计算血浆蛋白结合率．香叶木苷在血浆中药物质量浓度为1～90μg／mL范围内，其与大鼠血浆蛋白的结合率范围为29．83％～32．56％，波动较小，结果可靠．香叶木苷属于低血浆蛋白结合率药物，大部分药物分子以游离形式发挥药效．     

生长素结合蛋白研究进展

植物细胞感受生长素的信号是由生长素结合蛋白和生长素分子相结合。从而引起生长素信号传递的一系列级联反应而完成的．生长素与其结合蛋白的结合是生长素引发生理反应的第一步，也是必需的过程．     

The role of protein surface charges in ion binding

Protein engineering is a means of probing the role of electrostatic interactions in protein functions; this elegant technique has been applied to the elucidation of electrostatic effects in enzyme catalysis. Here we show how the use of mutant proteins allows the determination of the contributions of individual charges to the free energy of ion binding to proteins. We have investigated the importance of three negatively charged side chains in the binding of Ca2+ to bovine calbindin D9K (ref.2): these are clustered around the calcium sites but are not directly involved as ligands. Each of these charges is found to contribute approximately 7 kJ mol-1 to the free energy of binding of two Ca2+ ions and to affect the cooperativity of Ca2+ binding. The influence of surface charges on ion binding to proteins may be more common than generally supposed and could have important consequences for protein function.     

Mapping antibody binding sites on protein antigens.

The large surfaces of protein antigens that interact with antibody-combining sites can be determined using deuterium-exchange labelling and two-dimensional 1H nuclear magnetic resonance (NMR). This technique may also be applied to other protein-protein interactions to identify key residues that contribute to the affinity.     

DNA sequence determinants of CAP-induced bending and protein binding affinity

The sites of DNA bending induced by binding catabolite activator protein are identified and shown to coincide with positions where DNA grooves face the protein. The bendability of DNA with different sequences at these bend centres parallels the bending preference of the sequences in nucleosomal DNA. Anisotropic DNA bendability significantly affects the structure and strength of regulatory protein-DNA complexes.     

Regulation of glutamate receptor binding by the cytoskeletal protein fodrin

The erythrocyte cytoskeleton, which consists primarily of a meshwork of spectrin and actin, controls cell shape and the disposition of proteins within the membrane. Proteins similar to spectrin have recently been found in diverse cells and tissues, and it is possible that they mediate the capping of cell-surface receptors, although this has not been demonstrated directly. In neurones, the spectrin-like protein fodrin lines the cortical cytoplasm and may link actin filaments to the membrane. Fodrin has been hypothesized to regulate the number of receptor binding sites on neuronal membranes for the putative neurotransmitter L-glutamate. Micromolar calcium concentrations activate the thiol protease calpain I, induce fodrin degradation and more than double the density of glutamate binding sites; these effects are all blocked by thiol protease inhibitors. We have now used specific antibodies to examine further the role of fodrin proteolysis in regulating glutamate receptors. We report that fodrin antibodies block the fodrin degradation and increase in glutamate binding normally induced by calcium, and so provide direct evidence for control of membrane receptors by a non-erythroid spectrin.     

Phospholipid binding by a synaptic vesicle protein homologous to the regulatory region of protein kinase C

Neurotransmitters are released at synapses by the Ca2(+)-regulated exocytosis of synaptic vesicles, which are specialized secretory organelles that store high concentrations of neurotransmitters. The rapid Ca2(+)-triggered fusion of synaptic vesicles is presumably mediated by specific proteins that must interact with Ca2+ and the phospholipid bilayer. We now report that the cytoplasmic domain of p65, a synaptic vesicle-specific protein that binds calmodulin contains an internally repeated sequence that is homologous to the regulatory C2-region of protein kinase C (PKC). The cytoplasmic domain of recombinant p65 binds acidic phospholipids with a specificity indicating an interaction of p65 with the hydrophobic core as well as the headgroups of the phospholipids. The binding specificity resembles PKC, except that p65 also binds calmodulin, placing the C2-regions in a context of potential Ca2(+)-regulation that is different from PKC. This is a novel homology between a cellular protein and the regulatory domain of protein kinase C. The structure and properties of p65 suggest that it may have a role in mediating membrane interactions during synaptic vesicle exocytosis.