Although homo- and heterodimerizations of G protein-coupled receptors (GPCRs) are well documented, GPCR monomers are able to assemble in different ways, thus causing variations in the interactive interface between receptor monomers among different GPCRs. Moreover, the functional consequences of this phenomenon, which remain to be clarified, could be specific for different GPCRs. Synthetic peptides derived from transmembrane (TM) domains can interact with a full-length GPCR, blocking dimer formation and affecting its function. Here we used peptides corresponding to TM helices of bovine rhodopsin (Rho) to investigate the Rho dimer interface and functional consequences of its disruption. Incubation of Rho with TM1, TM2, TM4, and TM5 peptides in rod outer segment (ROS) membranes shifted the resulting detergent-solubilized protein migration through a gel filtration column toward smaller molecular masses with a reduced propensity for dimer formation in a cross-linking reaction. Binding of these TM peptides to Rho was characterized by both mass spectrometry and a label-free assay from which dissociation constants were calculated. A BRET (bioluminescence resonance energy transfer) assay revealed that the physical interaction between Rho molecules expressed in membranes of living cells was blocked by the same four TM peptides identified in our in vitro experiments. Although disruption of the Rho dimer/oligomer had no effect on the rates of G protein activation, binding of Gt to the activated receptor stabilized the dimer. However, TM peptide-induced disruption of dimer/oligomer decreased receptor stability, suggesting that Rho supramolecular organization could be essential for ROS stabilization and receptor trafficking.

Background: Structural determinants of aspartyl aminopeptidase (DNPEP) enzymatic activity have not yet been elucidated. Results: DNPEP contains a binuclear metal active site and forms a tetrahedral homo-dodecamer in solution. Conclusion: Manganese binding at the active site stimulates DNPEP activity. The tetrahedral assembly restricts peptide access to the active site. Significance: This study provides a structural and biochemical basis for understanding DNPEP physiology.

Background:The P23H opsin mutant causes the blinding human disease, retinitis pigmentosa. Results: Molecular properties of bovine P23H mutant opsin were characterized in both in vitro and a transgenic C. elegans model. Conclusion: Thermally unstable P23H isorhodopsin containing correct disulfide bond can be slowly regenerated in transgenic C. elegans. Significance: This study produced novel information about the disease-causing P23H mutant opsin.

Our findings indicate that these initial HTS and following assays can identify active therapeutic compounds, even for difficult targets such as mutant rhodopsin. The assays are readily scalable and their function has been proven with model compounds. High-throughput screening, supported by automated imaging and classic immunoassays, can further characterize multiple steps and pathways in the biosynthesis and degradation of this essential visual system protein.

Raman difference spectroscopy is used to probe the properties of a 36-nt RNA molecule, “D5”, which lies at the heart of the catalytic apparatus in group II introns. For D5 that has all its adenine residues labeled with 13C and 15N, and utilizing Raman difference spectroscopy, we identify the conformational sensitive -C-O-P-O-C- stretching modes of the unlabeled bonds adjacent to adenine bases, as well as the adenine ring modes themselves. The phosphodiester modes can be assigned to individual adenine residues based on earlier NMR data. The effect of Mg2+ binding was explored by analyzing the Raman difference spectra for [D5 + Mg2+] minus [D5 no Mg2+], for D5 unlabeled, or D5 labeled with 13C/15N-enriched adenine. In both sets of data we assign differential features to G ring modes perturbed by Mg2+ binding at the N7 position. In the A labeled spectra we attribute a Raman differential near 1450 cm−1 and changes of intensity at 1296 cm−1 to Mg binding at the N7 position of adenine bases. The A and G bases involved in Mg2+ binding again can be identified using earlier NMR results. For the unlabeled D5, a change in the C-O-P-O-C stretch profile at 811 cm−1 upon magnesium binding is due to a “tightening up” (in the sense of a more rigid molecule with less dynamic interchange among competing ribose conformers) of the D5 structure. For adenine labeled D5, small changes in the adenine backbone bond signatures in the 810 – 830 cm−1 region suggest small conformational changes occur in the tetraloop and bulge regions upon binding of Mg2+. The PO2− stretching vibration, near 1100 cm−1, from the non-bridging phosphate groups, probes the effect of Mg2+-hydrate inner-sphere interactions that cause an up-shift. In turn, the up-shift is modulated by the presence of monovalent cations since in the presence of Na+ and Li+ the up-shift is (23±2 cm−1) while in the presence of K+ and Cs+ it is (13±3 cm−1), a finding that correlates with the differences in hydration radii. These subtle differences in electrostatic interactions may be related to observed variations in catalytic activity. For a reconstructed ribozyme comprising domains 1–3 (D123) connected in cis plus domain 5 (D5) supplied in trans, cleavage of spliced exon substrates in the presence of magnesium and K+ or Cs+ is more efficient than that in the presence of magnesium with Na+ or Li+.