David R. Evans, Ph.D.

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Professor Area of interest: Pyrimidine biosynthesis Ph. D. Wayne State University, Detroit, MI, 1968 Evans Lab page e-mail: devans@cmb.biosci.wayne.edu Tel: 313-577-1016

We are studying the structure and function of large complex multidomain proteins. Much of our work focuses on the CAD, a 1.5 megadalton complex that catalyzes the initial steps in pyrimidine biosynthesis and regulates its activity. We are especially interested in the control mechanisms, such as allosteric regulation and phosphorylation, interdomain signaling that coordinates reactions occurring on distinct domains, and channeling by which the intermediates are sequestered within the complex and passed from site to site via intramolecular tunnels. The regulation of CAD by phosphorylation by various kinases implicated in cell growth is especially interesting. MAP kinase, activated when growth signals bind to extracellular receptors, phosphorylates a specific threonine residue on CAD, a modification that results in its activation and stimulation of pyrimidine biosynthesis. MAP kinase phosphorylation is antagonized by cyclic AMP dependent protein kinase A (PKA), which phosphorylates a distinct serine residue and leads to a decrease in CAD activity. We have evidence that CAD, MAP kinase, PKA and the phosphatase PP1 form a large signaling complex that is regulated by the phosphorylation of specific components. A second project is an investigation of the adaptive mechanisms of proteins isolated from hyperthermophiles that flourish near deep-ocean hydorthermal vents and hot springs at temperatures close to 100 ^o C. We recently cloned and expressed five proteins that initiate pyrimidine biosynthesis in Aquifex aeolicus, an ancient organism occupying the deepest branch on the eubacterial phylogenetic tree. The structure of these proteins is very unusual and confers the ability to sequester labile intermediates thus preventing their thermal degradation.