Functional Expression of Chemoreceptors with the Help of a Guanine Nucleotide Exchange Factor

Odorant receptors and other chemoreceptors are usually poorly expressed in the plasma membrane of heterologous cells. A key point of regulation in G protein-mediated signaling is the interconversion between the active GTP-bound and inactive GDP-bound states of the G alpha subunit, which regulatory proteins, such as guanine nucleotide exchange factors (GEFs), can control. GEFs stimulate formation of the GTP-bound state of G alpha and therefore are considered to work as positive regulators of G protein-coupled receptor signaling. Ric-8B, a GEF that is specifically expressed in olfactory sensory neurons, promotes functional expression of odorant receptors in HEK293T cells because it amplifies the initially low receptor signaling through G alpha olf. This same strategy could be used to functionally express other types of chemoreceptors.

Alkaloids from the Bark of Guatteria hispida and Their Evaluation as Antioxidant and Antimicrobial Agents

Phytochemical investigation of the bark of Guatteria hispida afforded three new alkaloids, 9-methoxy-O-methylmoschatoline (1), 9-methoxyisomoschatoline (2), and isocerasonine (3), along with 10 known alkaloids, 8-oxopseudopalmatine (4), O-methylmoschatoline (5), lysicamine (6), liriodenine (7), 10-methoxyliriodenine (8), nornuciferine (9), anonaine (10), xylopine (11), coreximine (12), and isocoreximine (13). The major compounds, 2, 6, 12, and 13, showed significant antioxidant capacity in the ORAC(FL), assay. Compounds 5, 6, and 7 were active against S. epidermidis and C. dubliniensis, with MIC values in the range 12.5-100 mu g mL(-1).