Photoaffinity labeling of a novel benzodiazepine binding protein in rat brain

Photoaffinity labeling of plasma proteins

Photoaffinity labeling is a powerful technique for identifying a target protein. A high degree of labeling specificity can be achieved with this method in comparison to chemical labeling. Human serum albumin (HSA) and α₁-acid glycoprotein (AGP) are two plasma proteins that bind a variety of endogenous and exogenous substances. The ligand binding mechanism of these two proteins is complex. Fatty acids, which are known to be transported in plasma by HSA, cause conformational changes and participate in allosteric ligand binding to HSA. HSA undergoes an N-B transition, a conformational change at alkaline pH, that has been reported to result in increased ligand binding. Attempts have been made to investigate the impact of fatty acids and the N-B transition on ligand binding in HSA using ketoprofen and flunitrazepam as photolabeling agents. Meanwhile, plasma AGP is a mixture of genetic variants of the protein. The photolabeling of AGP with flunitrazepam has been utilized to shed light on the topology of the protein ligand binding site. Furthermore, a review of photoaffinity labeling performed on other major plasma proteins will also be discussed. Using a photoreactive natural ligand as a photolabeling agent to identify target protein in the plasma would reduce non-specific labeling.

Mechanisms of action of anticonvulsant drugs

Understanding the mechanisms of action of anticonvulsant drugs has been a major research effort of neuroscientists for the last three decades. Numerous biochemical and electrophysiological processes have been shown to be modulated by anticonvulsant drugs. However, clear correlations of these effects with anticonvulsant activity are often difficult to determine. Over the last 5 years, several major research areas have developed that shed new light on the mechanisms of action of anticonvulsant drugs. Although a complete discussion of all aspects of anticonvulsant research are not possible in the scope of this article, a description of benzodiazepine receptors, mechanisms involved in neuronal sustaining repetitive firing, and calcium regulation of neuronal function have direct bearing on neuronal excitability and ultimately on anticonvulsant drug effect. Each of these major research areas has opened new insights into our understanding of molecular mechanisms of how anticonvulsant drugs work.

Characterization of a cytosolic protein (P36) isolated from pig brain by benzodiazepine-affinity chromatography

Benzodiazepine-affinity chromatography, on a column of 1012S-Sepharose, resulted in the detection and purification of a binding protein (P36) from the cytosolic fraction of pig cerebral cortex. Purified P36 was enriched over 3,500-fold in a single step and was recovered with an efficiency of 50-60%. Analysis of the purified preparation by sodium dodecyl sulphate-polyacrylamide gel electrophoresis demonstrated a single polypeptide of Mr 36,000. The Stokes radius (3.44 nm) and sedimentation coefficient (4.43S) indicated that purified P36 is a dimeric protein. Analysis of the amino acid composition of P36 revealed a relatively high content of the hydrophobic amino acids, valine and leucine. Immunoblotting of several pig tissue preparations with an antiserum raised against purified P36 demonstrated approximately equal enrichment of P36 in cerebral cortex, cerebellum, and adrenal glands. Lesser enrichment was observed in kidney and liver, whereas a number of other tissues displayed no immunoreactivity. The gamma-aminobutyrate/benzodiazepine receptor complex and P36 showed no immunological cross-reactivity. High-affinity binding activity for [3H]Ro 15-4513, [3H]flunitrazepam, or [3H]PK11195 was not detected in preparations of purified P36. However, the ability of the gamma-aminobutyrate/benzodiazepine receptor inverse agonists, methyl- and ethyl-beta-carboline-3-carboxylate, to inhibit the binding of P36 to 1012S-Sepharose at relatively low concentrations indicates that P36 exhibits a degree of binding specificity.