Ann Stock
	Professor Department of Biochemistry UMDNJ-Robert Wood Johnson Medical School Associate Investigator Howard Hughes Medical Institute Member Cancer Institute of New Jersey Ph.D., 1986, University of California, Berkeley Tel:  [732] 235-4844 Fax: [732] 235-5289 stock@cabm.rutgers.edu Stock Lab Website

Signal transduction, protein kinases, response regulators, receptor modification, bacterial chemotaxis, X-ray crystallography.

The goal of research in our laboratory is to understand the molecular mechanisms of receptor-mediated signal transduction. In particular, research is focused on elucidating structure/function relationships in proteins involved in information processing using a combination of molecular genetic, biochemical and X-ray crystallographic methods. Specific interest is directed toward investigating the role of covalent modifications of proteins in signaling pathways.

A large fraction of bacterial signal transduction systems utilize a common mechanism involving transfer of a high energy phosphoryl group from a histidine protein kinase to an aspartate residue of a response regulator protein. The regulatory domains of the response regulator proteins can be thought of as phosphorylation-activated switches that are turned on and off by phosphorylation and dephosphorylation. In the active, phosphorylated state, the conserved regulatory domains interact productively with other protein domains to activate specific effector functions such as flagellar rotation, regulation of transcription, or enzymatic catalysis. We have solved the crystal structures of several representative members of the response regulator family including the chemotaxis response regulator CheY, the chemotaxis receptor methylesterase, CheB, the DNA-binding domain of the winged-helix transcriptional regulator OmpR, and the transcription factor DrrD. These structures and correlated biochemical studies have provided insight into the mechanism of function of response regulators. Phosphorylation alters the conformation of the regulatory domain and the altered molecular surface is exploited for regulatory protein-protein interactions. Current efforts are focused on understanding the molecular details of these regulatory interactions through structural characterization of the active forms of these proteins in the context of protein-protein and protein-DNA complexes.

Additional structural studies are focused on families of unusual protein kinases. One project focuses on the conserved catalytic domains of bacterial histidine protein kinases. A second project is focused on a novel family of eukaryotic Ser/Thr protein kinases that bear no sequence resemblance to previously characterized Ser/Thr and Tyr protein kinases. The protein kinase we are presently studying is eEF2 kinase, a calmodulin-dependent kinase that phosphorylates elongation factor 2, resulting in inhibition of translation. This kinase is found at elevated levels in some tumors and its role in oncogenesis is being pursued by collaborators at the Cancer Institute of New Jersey.

Bacterial chemotaxis receptors are subject to reversible covalent modifications that modulate their signaling activities and allow for adaptation to stimuli. The transmembrane receptors are reversibly methylated at specific glutamate residues within their conserved cytoplasmic domains by an S-adenosylmethionine-dependent methyltransferase, CheR, and a methylesterase, CheB. The study of methylesterase CheB intersects with our interest in response regulator proteins (described above). Additionally, we have determined the structure of methyltransferase, CheR, bound to the inhibitor S-adenosylhomocysteine, providing the first structural information for a protein methyltransferase, and have also determined the structure of CheR bound to a fragment of the chemotaxis receptor for aspartate. Interactions between the methyltransferase and receptors are highly regulated, with the methylation state of the receptor influencing its susceptibility to further modification. Biochemical studies are directed at probing the regulatory interactions between the methyltransferase and the chemoreceptors.

Domain interactions of two response regulators. Methylesterase CheB and transcription factor DrrD are shown with their regulatory domains in similar orientations. Phosphorylation at the conserved aspartate (shown) induces structural perturbations in a surface of the regulatory domain (gold) resulting in activation of effector domain activities, the catalytic activity of CheB and the DNA-binding of DrrD. (CheB structure by S. Djordjevic, A. West & P. Goudreau; DrrD structure by D. Buckler)

Selected Publications1