Contact Information

Department of Chemistry and Biochemistry
Texas Tech University,
Lubbock TX, 79401

Tel: 806-742-1673
Fax: 806-742-0135

E-mail:
wdavid.nes@ttu.edu.

 

Introduction

 

     The major thrust of our research is to elucidate the molecular and genetic basis of sterol biosynthetic reactions and to elucidate the role sterol structure plays in biological activity and evolution.  Our goal is to establish a full understanding of sterol diversity as a prerequisite for the rational design  of medicinal drugs, antifungal and  antiinsect compounds  to control the production and processing of sterol synthesis in normal and diseased systems. We also are researching phytosterol homeostasis  to generate transgenic plants with modified sterol compositions  that possess value-added traits.

    For example, one area of interest is the study of a key enzyme in ergosterol synthesis responsible for the critical slow step controlling the transmethylation reaction at C-24 in the fungal sterol side chain, the sterol methyl transferase (SMT).   The C-24 methyl group is an essential feature to the role of sterols in fungal physiology. Animals do not synthesize 24-alkyl sterols. Differences in sterol structure between animals and fungi (particularly opportunistic pathogens)  provide a unique opportunity to develop rational control of disease through differences in sterol synthesis. Thus, we are attempting to understand the catalytic mechanism and structure of SMTs from different sources. Specifically, we have cloned, sequenced and generated large amounts of pure recombinant SMT to study its catalysis. Using a mechanism-based approach we have designed a set of substrate, transition state and product analogs which to inhibit enzyme activity. It appears that some of these compounds have the potential to serve as taxa-specific inhibitors with high specific activity.

    A few other specific systems that are under investigation are the human sterol 8-to-7 isomerase (in cooperation with AstraZeneca Pharmaceutical), which we have overexpressed in bacteria and yeast and the 14a-demethylase enzyme from Mycobacterium tuberculosis (in cooperation with Michael Waterman at Vanderbilt Medical School) which we have overexpressed in bacteria. In both cases, we have studied  the pure enzyme kinetically. We have also generated transgenic plants with modified phytosterol compositions (in cooperation with Henry Nguyen at Texas Tech University). We have introduced foreign SMT genes from yeast into tobacco and tomato plants and utilized antisense technology to impair SMT activity in these plants. Finally, we have determined that the classic acetate/mevalonate pathway to ergosterol is not operational in the yeast-like Prototheca wickerhamii which synthesizes its sterol from the mevalonate-independent pathway.

    Students, Post-doctoral Research Associates and Visiting Scientists get training in my laboratory in organic synthesis, analysis, biochemistry, enzymology, molecular biology and microbiology. The techniques and experimental approaches developed in this laboratory are expected to be broadly applicable to the understanding of enzyme mechanistic and biosynthetic investigations.

 

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