The goal of Dr. Klee and her colleagues is to elucidate the mechanism of stimulus-response coupling mediated by Ca2+ and calmodulin. The regulation of calcineurin, the only protein phosphatase under the control of calmodulin, is used as a model system. Calcineurin, the target of immunosuppressive drugs, plays a critical role in the regulation of genes involved in cellular processes as diverse as T cell activation, cell differentiation, cardiac hypertrophy, and long term memory. Calcineurin activity is regulated by two, structurallysimilar, but functionally distinct Ca2+-binding proteins: calcineurin B, an integral subunit of the enzyme, and calmodulin. Thedisplacement of an inhibitory domain during the Ca2+-dependent binding of calmodulin to calcineurin results in a large activation ofcalcineurin affecting the Vmax of the enzyme, which is followed by a Ca2+/calmodulin- and time-dependent reversible inactivation. The identification of calcineurin as an [Fe2+-Zn2+] protein phosphatase by M. Ghosh in collaboration with J. Zweier at Johns Hopkins University provided a mechanism for this inactivation that is the result of exposure of Fe2+ at the active site facilitating its oxidation by superoxide anion. Thus, we have uncovered a novel coupling of the regulation of protein phosphorylation by Ca2+ and oxidative stress. The nature of the conformational changes that accompany Ca2+ binding to calmodulin and allow it to activate calcineurin are presently under study in collaboration with Ad Bax (NIDDK). In contrast to calmodulin, calcineurin B is tightly bound to calcineurin A even in the absence of Ca2+ (Kd=10-14M-1), but Ca2+ binding to its three moderate affinity sites is required for activity and calmodulin binding. The Ca2+-binding properties of calcineurin B and the identification of the high and moderate affinity Ca2+ sites has been analyzed by flow dialysis (X. Wang and Z. Gao) and Fourier Transformed Infrared spectroscopy in collaboration with Jill Trewhella (Los Alamos National Laboratory) using calcineurin B mutants deficient in Ca2+ binding to each one of the four Ca2+ sites. A conformational change of the regulatory domain of calcineurin A that accompanies Ca2+ binding to calcineurin B has been identified by Seun-Ah Yang. It provides a mechanism to explain the previously reported dependence of Ca2+ binding to calcineurin B for calmodulin activation and the large increase in Ca2+ affinity of calcineurin for Ca2+ upon removal of the calmodulin- binding domain (Stemmer and Klee, Biochemistry 33: 6859-66, 1994). - Calcineurin, Calcium, Calmodulin, Immunosuppression, Iron, Oxidation, Superoxide dismutase, Protein phosphatases, - Neither Human Subjects nor Human Tissues

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Intramural Research (Z01)
Project #
1Z01BC005231-25
Application #
6289080
Study Section
Special Emphasis Panel (LB)
Project Start
Project End
Budget Start
Budget End
Support Year
25
Fiscal Year
1999
Total Cost
Indirect Cost
Name
National Cancer Institute Division of Basic Sciences
Department
Type
DUNS #
City
State
Country
United States
Zip Code