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Michael E Baker

Publications and source records attributed to Michael E Baker.

4 recordsLinked to original sources
PubMed2003

Inhibition of 11 beta-hydroxysteroid dehydrogenase type 2 by dithiocarbamates.

Dithiocarbamates (DTCs), important therapeutic and industrial chemicals released in high quantities into the environment, exhibit complex chemical and biological activities. Here, we demonstrate an effect of DTCs on glucocorticoid action due to inhibition of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) type 2, converting cortisol to cortisone in the kidney, but not 11 beta-HSD1, catalyzing the reverse reaction in liver and adipose tissue. Thus, DTCs may locally increase active glucocorticoid concentrations. Preincubation with the DTC thiram abolished 11 beta-HSD2 activity, suggesting irreversible enzyme inhibition. The sulfhydryl protecting reagent dithiothreitol blocked thiram-induced inhibition and NAD+ partially protected 11 beta-HSD2 activity, indicating that DTCs act at the cofactor-binding site. A 3D-model of 11 beta-HSD2 identified Cys90 in the NAD(+)-binding site as a likely target of DTCs, which was supported by a 99% reduced activity of mutant Cys90 to serine. The interference of DTCs with glucocorticoid-mediated responses suggests a cautious approach in the use of DTCs in therapeutic applications and in exposure to sources of DTCs such as cosmetics and agricultural products by pregnant women and others.

11-beta-Hydroxysteroid Dehydrogenase Type 2↗
PubMed2003

Glutamate-115 renders specificity of human 11beta-hydroxysteroid dehydrogenase type 2 for the cofactor NAD+.

The renal 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 2 catalyzes the NAD(+)-dependent oxidation of the C11-alcohol on cortisol and corticosterone to yield inactive 11-ketosteroids. The lack of purified active enzyme complicates structure-function analyses of 11beta-HSD2. Here, we constructed a 3D-structural model of 11beta-HSD2, based on known 3D-structures of other short-chain dehydrogenases/reductases (SDR), and functionally analyzed 11beta-HSD2 mutants predicted to be involved in cofactor binding. Our 3D-model explains the preference for NAD(+) over NADP(+) by the coulombic repulsion between the adenosine ribose 2'-phosphate on NADP(+) and the carboxylate on Glu(115) and to steric hindrance with the side chain on Glu(115). Indeed, replacement of Glu(115) with serine or threonine, lacking repulsive charge and unfavorable steric interactions, showed only 3-fold preference for NAD(+), compared to 40-fold for wild-type 11beta-HSD2. Mutation of both Asp(91) and Glu(115) to serine raised NADP(+)-dependent activity to that with NAD(+), but caused reduced enzymatic activity. The 3D-model predicted that this is due to a loss of stabilizing interactions of Asp(91) with Cys(90), Glu(115), Asn(117) and Gly(120). Thus, predictions using the 3D-model combined with analysis of mutants allowed the identification of residues critical for NAD(+)-dependent activity of 11beta-HSD2.

11-beta-Hydroxysteroid Dehydrogenase Type 2↗
PubMed2003

Evolution of adrenal and sex steroid action in vertebrates: a ligand-based mechanism for complexity.

Various explanations have been proposed to account for complex differentiation and development in humans, despite the human genome containing only two to three times the number of genes in invertebrates. Ignored are the actions of adrenal and sex steroids-androgens, estrogens, glucocorticoids, mineralocorticoids, and progestins-which act through receptors that arose from an ancestral nuclear receptor in a protochordate. This ligand-based mechanism is unique to vertebrates and was integrated into the already robust network of transcription factors in invertebrates. Adrenal and sex steroids influence almost all aspects of vertebrate differentiation and development. I propose that evolution of this ligand-based mechanism in a primitive vertebrate was an important contribution to vertebrate complexity. Sequencing of genomes from a cephalochordate, such as amphioxus, and from hagfish and lamprey will establish early events in the evolution of steroid hormone signaling, and also allow genetic studies to elucidate how vertebrate complexity depends on steroid hormones.

Adrenal Cortex Hormones↗