Two amino acid differences in the sixth transmembrane domain are partially responsible for the pharmacological differences between the 5-HT1D beta and 5-HT1E 5-hydroxytryptamine receptors.

5-Hydroxytryptamine elicits its physiological effects by interacting with a diverse group of receptors. Two of these receptors, the 5-HT1D beta and the 5-HT1E receptors, are approximately 60% identical in the transmembrane domains that presumably form the ligand binding site yet have very different pharmacological properties. Analysis of the pharmacological properties of a series of chimeric 5-HT1D beta/5-HT1E receptors indicates that sequences in the sixth and seventh transmembrane domains are responsible for the differential affinity of 5-carboxamidotryptamine for these two receptors. More detailed analysis shows that two amino acid differences in the sixth transmembrane domain (Ile333 and Ser334 in the 5-HT1D beta receptor, corresponding to Lys310 and Glu311 in the 5-HT1E receptor) are largely responsible for the differential affinities of some, but not all, ligands for the 5-HT1D beta and 5-HT1E receptors. It is likely that these two amino acids subtly determine the overall three-dimensional structure of the receptor rather than interact directly with individual ligands.

Identification of a novel hypothalamic neuropeptide Y receptor associated with feeding behavior.

Neuropeptide Y (NPY) plays important roles in the central control of appetite and energy balance, but the receptor subtype responsible for this function has not been cloned. Here we report the cloning by expression of a novel NPY receptor subtype from a rat hypothalamus cDNA library. The novel receptor, referred to as the NPY Y5 receptor, has a transcript of approximately 2.6 kilobases with an open reading frame of 1335 base pairs that encodes a 445-amino acid protein. The amino acid sequence deduced from the rat Y5 cDNA clone shows only 30-33% identity to other NPY receptors, including Y1, Y2, and Y4/PP1. Using the rat Y5 receptor cDNA probe, the human homologue was obtained by low stringency hybridization. The human Y5 amino acid sequence has 88% identity to the rat Y5 receptor. Importantly, pharmacological analysis shows that the rat and human Y5 receptors have high affinity for the peptides that elicit feeding (e.g. NPY, PYY, (2-36)NPY, and (LP)NPY) and low affinity for nonstimulating peptides (e.g. (13-36)NPY and rat PP), suggesting that it is the NPY feeding receptor subtype.

Processing of the beta-amyloid precursor protein carrying the familial, Dutch-type, and a novel recombinant C-terminal mutation.

Mutations within the beta-amyloid precursor protein (beta-APP) gene that cosegregate with early onset familial Alzheimer's disease (FAD) and hereditary cerebral hemorrhage with amyloidosis of the Dutch-type (HCHWA-D) have been reported. The effects of these mutations on the products of both the non-amyloidogenic and potentially amyloidogenic processing pathways of the beta-APP protein were examined in stably transfected cells. Processing of these mutants appeared to be the same as wild-type. These results contrasted sharply to those observed with a mutation near the amino terminus of the beta-protein domain of beta-APP. This mutation resulted in a two-fold decrease of a potentially amyloidogenic 11 kDa peptide fragment. The data suggest that the FAD and HCHWA-D mutations have no effect on the formation of potentially amyloidogenic fragments in this cell system, possibly implicating an alternative mechanism for their effects.