MOLECULAR BIOLOGICAL APPROACHES TO STUDYING TRACE MINERALS - WHY SHOULD CLINICIAN CARE

The approaches and tools of molecular biology have been enormously val uable to all branches of biological science over the last decade. Nutr ition is no exception, where studies on the influence of nutrients on gene expression and of gene products on nutrient metabolism have resul ted in a much more sophisticated and detailed understanding of nutriti onal biochemistry. An example of this as applied to trace mineral rese arch can be seen in the area of thyroidology. Until recently, the sole link between thyroid hormones and trace minerals was iodide. Then the thyroid hormone receptor was cloned and analysis of the protein codin g sequence showed it to be a member of a large family of gene activati ng receptor proteins. These all possess a region containing two cluste rs of cysteine residues, thought to chelate zinc, which is required fo r binding of the receptors to their target genes. Zinc appears to be n ecessary for the biological functioning of not only the thyroid hormon e receptor but also many other nuclear proteins which regulate gene ex pression. The principal product of the thyroid gland is thyroxine from which the more active form of the hormone, triiodothyronine, is deriv ed by peripheral monodeiodination. One of the two enzymes responsible, type I 5'-iodothyronine deiodinase, was recently cloned and shown to contain selenocysteine. Thus production of the active thyroid hormone is dependent on selenium status. These advances made with molecular bi ology have important implications for clinicians. The possibilities fo r understanding the clinical picture are immediately enhanced, improvi ng both diagnosis and treatment. Molecular biology also provides the o pportunity for developing more specific and sensitive tools for assess ing nutritional status. Diseases with a genetic basis can be unequivoc ally diagnosed and perhaps even treated. A strength of nutrition is th at it encompasses molecular biology and clinical practice and practiti oners of each can benefit from an understanding of the complementary a rea.