Inactivation of dopamine beta-hydroxylase by beta-ethynyltyramine: kinetic characterization and covalent modification of an active site peptide

AMG 837: a potent, orally bioavailable GPR40 agonist

The discovery that certain long chain fatty acids potentiate glucose stimulated insulin secretion through the previously orphan receptor GPR40 sparked interest in GPR40 agonists as potential antidiabetic agents. Optimization of a series of β-substituted phenylpropanoic acids led to the identification of (S)-3-(4-((4'-(trifluoromethyl)biphenyl-3-yl)methoxy)phenyl)hex-4-ynoic acid (AMG 837) as a potent GPR40 agonist with a superior pharmacokinetic profile and robust glucose-dependent stimulation of insulin secretion in rodents.

Molecular modelling approaches to host-guest complexes

Host-guest interactions can be modelled as a non-bonding recognition process using long-range electrostatic forces. By using molecular isopotential maps the differences between the methotrexate-dihydrofolate reductase and folate-dihydrofolate reductase complexes can be predicted. By extending the technique to molecule-molecule docking the interaction of formamide with the crown ether 18-crown-6 can be simulated with reasonable accuracy. The closely related problem of predicting the separation of enantiomers of chiral molecules by chromatography has been attempted with encouraging results. A preliminary report is presented on the progress being made towards a better model for simulating stacking arrangement of pi systems by charge distribution.

The normal range for secondary Swain-Schaad exponents without tunneling or kinetic complexity

An analysis is presented of the range of secondary Swain-Schaad exponents to be expected at 25 degrees C in the absence of tunneling or kinetic complexity. From 15 996 sets of exact harmonic semiclassical equilibrium isotope effects for simple C-H/D/T exchange reactions and 954 sets of exact harmonic semiclassical secondary H/D/T kinetic isotope effects for C-H positions in simple organic reactions, the distribution of Swain-Schaad exponents versus magnitude of the isotope effect is determined. This distribution defines when a secondary Swain-Schaad exponent may be considered to implicate nonsemiclassical behavior, revises the expected Swain-Schaad exponent for extrapolation of secondary isotope effects, and serves as a guide to the uncertainty in such extrapolations.

The local minima method (LMM) of pharmacophore determination: a protocol for predicting the bioactive conformation of small, conformationally flexible molecules

Software has been developed for potential energy surface analysis and the local minima method of pharmacophore determination. LMM is rigorous and systematic and employs multiple conformations which are the local minima from the potential energy surface of each compound in the data set. It produces a series of possible pharmacophores from a postulated set of pharmacophore elements. The best pharmacophore is then determined by performing a comparative molecular field analysis (CoMFA) on each one. The pharmacophore which produces the most self-consistent model is deemed the best. Local minima on the gas-phase potential energy surface are shown to be a reasonably close approximation to protein bound conformations, and these conformations can be found through systematic conformational searches followed by minimization of the local minima. LMM was used to develop a 3D-QSAR model for dopamine beta-hydroxylase (DBH) inhibitors which was highly predictive (predictive R2 = 0.71 and standard error of predictions = 0.41). The model predicted that the phenyl and thienyl series of inhibitors were acting as bioisosteres. Examination of compounds overlayed in the model indicated a possible hydrogen bond acceptor in the DBH active site. Three tyrosine residues previously labeled by mechanism based inhibitors may be acting as the acceptor and therefore represent excellent candidates for site-directed mutagenesis studies.

A natural variant of bovine dopamine beta-monooxygenase with phenylalanine as residue 208: purification and characterization of the variant homo- and heterotetramers of (F208)4 and (F208)2(L208)2

Bovine dopamine beta-monooxygenase was purified from each of 18 individual adrenal glands by the method we have developed for the rapid purification of the enzyme from a single adrenal gland. Differential peptide mapping of the 18 enzyme preparations following fluorescence labeling of their cysteine residues revealed the presence of a novel variant with Phe as residue 208 in 14 adrenal glands; seven of them were homozygous for the variant allele and the remaining seven heterozygous. The variant enzyme was a tetramer and exhibited kinetic and structural properties similar to those of the wild-type tetramer (L208)4. These results indicate an allelic polymorphism and codominant expression of the two alleles of the enzyme gene.

Characterization of Drosophila tyramine beta-hydroxylase gene and isolation of mutant flies lacking octopamine

Octopamine is likely to be an important neuroactive molecule in invertebrates. Here we report the molecular cloning of the Drosophila melanogaster gene, which encodes tyramine beta-hydroxylase (TBH), the enzyme that catalyzes the last step in octopamine biosynthesis. The deduced amino acid sequence of the encoded protein exhibits 39% identity to the evolutionarily related mammalian dopamine beta-hydroxylase enzyme. We generated a polyclonal antibody against the protein product of T beta h gene, and we demonstrate that the TBH expression pattern is remarkably similar to the previously described octopamine immunoreactivity in Drosophila. We further report the creation of null mutations at the T beta h locus, which result in complete absence of TBH protein and blockage of the octopamine biosynthesis. T beta h-null flies are octopamine-less but survive to adulthood. They are normal in external morphology, but the females are sterile, because although they mate, they retain fully developed eggs. Finally, we demonstrate that this defect in egg laying is associated with the octopamine deficit, because females that have retained eggs initiate egg laying when transferred onto octopamine-supplemented food.

The effect of the inactive mutation on longevity, sex, rhythm and resistance to p-cresol in Drosophila melanogaster

Flies carrying the inactive (iav) mutation exhibit low locomotor activity and poor mating success, both of which are associated with a deficiency in the putative neurotransmitter, octopamine. Several other aspects of the iav mutant phenotype are described here. Male and female iav mutants show a small reduction in longevity but it is not clear whether this is a consequence of the iav mutation or their inactive phenotype. Young iav males show extended attractiveness to older courting males, which supports the notion that the iav gene has a role in post-eclosional maturation. The eclosion rhythm of iav mutants is normal, discounting the possibility of a role for octopamine in the maintenance of circadian rhythm. Flies carrying the iav mutation are highly susceptible to the octopamine analogue p-Cresol. Other phenotypically inactive flies show wild type levels of p-Cresol resistance. This is attributed to the deficiency of octopamine in iav mutants because low octopamine levels may be unable to out-compete the toxic effect of p-Cresol. Some inferences on the possible mode of action of the iav gene product are discussed.

Mouse dopamine beta-hydroxylase: primary structure deduced from the cDNA sequence and exon/intron organization of the gene

Genomic clones for mouse dopamine beta-hydroxylase (DBH) were isolated from two genomic libraries derived from DBA/2J and 129/SV mouse strains, by plaque hybridization with the human DBH cDNA probe. Subsequently, cDNA encoding mouse DBH was amplified with reverse transcription-polymerase chain reaction (RT-PCR) method using primers corresponding to 5'- and 3'-portions of the mouse DBH mRNA, subcloned into a plasmid vector, and subjected to nucleotide sequence analysis. The clone encoded a protein of 621 amino acids with a calculated molecular mass of 70,186 daltons. The predicted amino acid sequence of mouse DBH showed 87%, 80% and 79% identities with the rat, bovine and human enzymes, respectively. Several potential amino acid sequences that are involved in the posttranslational modification and catalytic function of DBH were identified in mouse DBH protein. Nucleotide sequence analysis of the overlapping genomic clones showed that the mouse DBH gene was composed of 12 exons about 17 kb in length. Typical TATA and CCAAT boxes were observed in the 5'-upstream region of the gene. Northern blot analysis of adrenal gland RNA detected a single size species of the mouse DBH mRNA.

The involvement of free radicals in the mechanisms of monooxygenases

The occurrence of free radicals in the mechanisms of monooxygenases reflects the chemistry of dioxygen and the inertness of typical substrates. Thus, oxidation of such substrates requires attack by reduced dioxygen-derived free radicals. Consequently, a molecule of NAD(P)H must be invested for each substrate molecule oxidized. Furthermore, since free radicals are difficult to control, deviations from the intended reaction course are frequent. These considerations are illustrated by examination of the generation and fate of enzyme- and substrate-derived free radicals at various stages in the catalytic cycles of two monooxygenases important in xenobiotic biotransformation, dopamine beta-hydroxylase and cytochrome P-450.

Bovine dopamine beta-hydroxylase, primary structure determined by cDNA cloning and amino acid sequencing

A cDNA clone encoding bovine dopamine beta-hydroxylase (DBH) has been isolated from bovine adrenal glands. The clone hybridizes to two oligonucleotide probes, one based on a previously reported active site peptide [DeWolf, W. E., Jr., et al. (1988) Biochemistry 27, 9093-9101] and the other based on the human DBH sequence [Lamouroux, A., et al. (1987) EMBO J. 6, 3931-3937]. The clone contains a 1.9-kb open reading frame that codes for the soluble form of bovine DBH, with the exception of the first six amino acids. Direct confirmation of 93% of the cDNA-derived sequence was obtained from cleavage peptides by protein sequencing and mass spectrometry. Differences were found between these two sequences at only two positions. Of the four potential N-linked carbohydrate attachment sites, two, Asn-170 and Asn-552, were shown to be partially and fully glycosylated, respectively. Within the 69% of the protein sequence confirmed by mass spectrometry, no other covalent modifications were detected.

Molecular cloning, structure, and expression of dopamine-beta-hydroxylase from bovine adrenal medulla

Dopamine-beta-hydroxylase (DBH), the enzyme that catalyzes the conversion of dopamine to norepinephrine, remains the topic of many unanswered questions. We isolated DBH cDNA clones from a bovine adrenal medulla cDNA library in the vector lambda gt10. The longest cDNA had an open reading frame encoding an entire mature DBH 578 amino acid (64,808 dalton) polypeptide chain, though lacking a portion of the signal peptide. Additional 5' clones, obtained by the polymerase chain reaction, established the sequence of a 19 amino acid signal peptide. The mature protein sequence was 84% homologous to that of human pheochromocytoma DBH, including preservation of four potential copper ligand sites (HH or HXH) and substrate binding domains. There were no hydrophobic (putative membrane spanning) domains, other than the signal peptide. All available DBH peptide and protein sequence data can be accounted for by the cDNA-deduced 578 amino acid mature protein primary structure. Prokaryotic DBH expression yielded a 65-kilodalton DBH-immunoreactive peptide that differed from eukaryotic adrenal DBH only in N-linked, endoglycosidase F-sensitive glycosylation in the latter. Southern analysis suggested one DBH gene, whereas Northern analysis suggested a single 2.6 kbp tissue-specific DBH transcript. Comparison of the DBH primary structure with other reported sequences [Protein Identification Resource (PIR), New Atlas (NEWAT)] did not indicate that DBH is a member of any known gene family. The results suggest that a single DBH gene encodes a message specifying a single DBH polypeptide chain.

Rat dopamine beta-hydroxylase: molecular cloning and characterization of the cDNA and regulation of the mRNA by reserpine

A number of cDNA clones for rat dopamine beta-hydroxylase (DBH) were isolated from a rat pheochromocytoma tumor cDNA library. The 2445 nucleotide sequence revealed a single open reading frame of 1860 nucleotides and a 3' untranslated region containing two polyadenylation addition signals. The cDNA coded for a 620 amino acid protein of 69,883 daltons. Six potential glycosylation sites and one potential phosphorylation site were identified. Amino acid residues likely to be involved in the active site of DBH and in copper ligand binding were identified. The N-terminal 42 amino acids appeared to constitute a typical but unusually long signal sequence. Hydropathy analysis indicated that this N-terminal region contained the only extensive hydrophobic domain and thus constituted the only obvious potential membrane attachment site. Northern analysis detected two mRNA species of 2.5 and 2.7 kb. The relative abundance of the 2.7 vs. 2.5 kb mRNAs was differentially regulated in PC12 cells and adrenals. DBH mRNA levels were induced in vivo in rat adrenals upon treatment with reserpine.

Structure of bovine adrenal dopamine beta-monooxygenase, as deduced from cDNA and protein sequencing: evidence that the membrane-bound form of the enzyme is anchored by an uncleaved signal peptide

A full-length cDNA for dopamine beta-monooxygenase (D beta M) from bovine adrenal glands has been cloned and sequenced. The soluble and membrane-derived forms of D beta M have also been sequenced from their N-termini. While the observed sequences for the soluble protein correspond to those previously reported [Joh, T.H., & Hwang, O. (1986) Ann. N.Y. Acad. Sci. 493, 343-350], the heavy subunit of membrane-derived enzyme is found to contain a unique N-terminus. Alignment of this N-terminus with that deduced from cDNA cloning indicates identity at 22 (and possibly 26) out of 27 residues. This comparison leads us to conclude that the membranous form of bovine D beta M retains an uncleaved N-terminal signal peptide as the source of membrane anchoring.

Sequence similarity between dopamine beta-hydroxylase and peptide alpha-amidating enzyme: evidence for a conserved catalytic domain

A comparison of human dopamine beta-hydroxylase (EC 1.14.17.1) with bovine peptide C-terminal alpha-amidating enzyme (EC 1.14.17.3), revealed a 28% identity extending throughout a common catalytic domain of approximately 270 residues. The shared biochemical properties of these two enzymes from neurosecretory granules suggests that the sequence similarity reflects a genuine homology and provides a structural basis for a new family of copper type II, ascorbate-dependent monooxygenases.