We have crystallized a complex of human TGF-beta1 with the human type II TGF-beta receptor. The size of these crystals are still less than the optimum for X-ray diffraction. Currently, we are trying a number of experiments to obtain larger crystals. Natural killer (NK) cells employ a set of cell surface receptors termed killer inhibitory receptors (KIR) to confer selective protection on target cells from NK-mediated lysis. Through a collaboration within the LMS, we have constructed a baculovirus expression system to express at least two different p58 NK receptors. Milligram amounts of receptor proteins have been expressed and purified. Crystallization experiments are in progress. We have crystallized and determined the three dimensional structure of formate dehydrogenase H from E. coli in its oxidized, reduced and an inhibitor bound forms. The enzyme contains multiple redox centers, which include a molybdopterin cofactor, an iron-sulfur cluster and a natural selenocysteine residue at its active site. Due to the unique composition of cofactors, E. coli formate dehydrogenase H not only carries out the redox reaction at the molybdenum center like other molybdenum-molybdopterin containing enzymes, but in addition, it also facilitates the transfer of the two electrons, obtained during the oxidation of its substrate formate, from the molybdenum center to downstream electron acceptors through part of its cofactors, an iron-sulfur cluster. The structure was determined using a combination of multiple isomorphous replacement method, and the multiwavelength anomalous dispersion technique. The resolution of the refined structures are 2.3, 2.8, 2.8 angstroms for the reduced, oxidized and the inhibitor bound forms, respectively. The results allow us to propose a catalytic mechanism that may be general to all members of this enzyme family.
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