The D/D genotype of the alpha2B-adrenoceptor is a novel genetic risk factor for acute coronary events, but not for hypertension.

The isomerization and decomposition dynamics of the simplest Criegee intermediate CH2 OO have been studied by classical trajectory simulations using the multireference ab initio MR-PT2 potential on the fly. A new, accelerated algorithm for dynamics with MR-PT2 was used. For an initial temperature of 300 K, starting from the transition state from CH2 OO→CH2 O2  , the system reaches the dioxirane structure in around 50 fs, then isomerizes to formic acid (in ca. 2800 fs), and decomposes into CO+H2 O at around 2900 fs. The contributions of different configurations to the multiconfigurational total electronic wave function vary dramatically along the trajectory, with diradical contributions being important for transition states corresponding to H-atom transfers, while being only moderately significant for CH2 OO. The implications for reactions of Criegee intermediates are discussed.

The alpha2-adrenergic receptors (alpha2-ARs) mediate signals to intracellular second messengers via guanine nucleotide binding proteins. Three human genes encoding alpha2-AR subtypes (alpha2A, alpha2B, alpha2C) have been cloned. Several chemical compounds display subtype differences in their binding and/or functional activity. Site-directed mutagenesis and molecular modeling are new tools with which to investigate the subtype selectivity of ligands. In this study, we introduce a new approach to mapping of the binding site crevice of the human alpha2A-AR. Based on a three-dimensional receptor model, we systematically mutated residues 197-201 and 204 in the fifth transmembrane domain of the human alpha2A-AR to cysteine. Chloroethylclonidine, an alkylating derivative of the alpha2-adrenergic agonist clonidine, binds irreversibly to alpha2A-ARs by forming a covalent bond with the sulfhydryl side chain of a cysteine residue exposed in the binding cavity, leading to inactivation of the receptor. Irreversible binding of chloroethylclonidine was used as a criterion for identifying introduced cysteine residues as being exposed in the binding cavity. The results supported a receptor model in which the fifth transmembrane domain is alpha-helical, with residues Val197, Ser200, Cys201, and Ser204 exposed in the binding pocket. Residues Ile198, Ser199, Ile202, and Gly203 face the lipid bilayer of the plasma membrane. This approach emerges as a powerful tool for structural characterization of the alpha2-ARs.

The alpha2-adrenergic receptors mediate part of the actions of the catecholamines noradrenaline and adrenaline on the regulation of energy balance. As part of an ongoing study on the genetics of obesity, the entire coding sequence of the alpha2B-adrenoceptor gene was screened in 58 obese, nondiabetic Finns by PCR-single stranded conformational analysis (PCR-SSCA). A polymorphism that leads to a deletion of 3 glutamic acids from a glutamic acid repeat element (Glu x 12, amino acids 297-309) present in the third intracellular loop of the receptor protein was identified. This repeat element has previously been shown to be important for agonist-dependent receptor desensitization. Of 166 genotyped subjects, 47 (28%) had 2 normal (long) alleles (Glu12/Glu12), 90 (54%) were heterozygous (Glu12/Glu9), and 29 (17%) were homozygous for the short (Glu9/Glu9) form. The basal metabolic rate, determined by indirect calorimetry and adjusted for fat-free body mass, fat mass, sex, and age, was 94 Cal/day (5.6%) lower (95% confidence interval for difference, 32, 156) in subjects homozygous for the short allele than in subjects with two long alleles (F = 4.84; P = 0.009, by ANOVA). Thus, a genetic polymorphism of the alpha2B-adrenoceptor subtype can partly explain the variation in basal metabolic rate in an obese population and may therefore contribute to the pathogenesis of obesity.