Calcineurin (CaN) is a calcium- and calmodulin-dependent protein serine/threonine phosphate which is critical for several important cellular processes, including T-cell activation. CaN is the target of the immunosuppressive drugs cyclosporin A and FK506, which inhibit CaN after forming complexes with cytoplasmic binding proteins (cyclophilin and FKBP12, respectively). We report here the crystal structures of full-length human CaN at 2.1 A resolution and of the complex of human CaN with FKBP12-FK506 at 3.5 A resolution. In the native CaN structure, an auto-inhibitory element binds at the Zn/Fe-containing active site. The metal-site geometry and active-site water structure suggest a catalytic mechanism involving nucleophilic attack on the substrate phosphate by a metal-activated water molecule. In the FKBP12-FK506-CaN complex, the auto-inhibitory element is displaced from the active site. The site of binding of FKBP12-FK506 appears to be shared by other non-competitive inhibitors of calcineurin, including a natural anchoring protein.

Density-dependent expression of luminescence in Vibrio harveyi is regulated by the concentration of an extracellular signal molecule (autoinducer) in the culture medium. A recombinant clone that restored function to one class of spontaneous dim mutants was found to encode functions necessary for the synthesis of, and response to, a signal molecule. Sequence analysis of the region encoding these functions revealed three open reading frames, two (luxL and luxM) that are required for production of an autoinducer substance and a third (luxN) that is required for response to this signal substance. The LuxL and LuxM proteins are not similar in amino acid sequence to other proteins in the database, but the LuxN protein contains regions of sequence resembling both the histidine protein kinase and the response regulator domains of the family of two-component, signal transduction proteins. The phenotypes of mutants with luxL, luxM and luxN defects indicated that an additional signal-response system controlling density-dependent expression of luminescence remains to be identified.

The majority of the VEGFR2 KID residues are not necessary for kinase activity. The unique structure observed for the ends of the KID may also occur in other PDGFR family members and may serve to properly orient the KID for signal transduction. This VEGFR2 kinase structure provides a target for design of selective anti-angiogenic therapeutic agents.

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. 171:240-2414, 1989). Mutants with transposon insertions in this regulatory locus were used to construct a hybridization probe which was used in this study to Luminescent bacteria are widespread in the marine environment, where they exist planktonically and as parasites and light organ symbionts. Light production by symbiotic bacteria living in association with higher organisms may serve to attract prey, for intraspecies communication, or to escape from predators (34). Luminescence could also function to provide a direct benefit to the bacteria. One possibility is that the luminescence system is used as a terminal oxidase when the cytochrome electron transport system cannot be synthesized (low iron availability) or cannot function (low oxygen tension) (26). Luciferase, a mixed function oxidase consisting of a and I subunits, catalyzes the emission of light (Fig. 1). In the generation of light, luciferase oxidizes a reduced flavin, FMNH2, and a longchain fatty aldehyde producing oxidized flavin and the corresponding fatty acid (22). A fatty acid reductase unique to the bioluminescence system functions to synthesize or recycle the aldehyde substrate. Expression of cloned genes for luciferase and fatty acid reductase is sufficient for the production of light in a variety of nonluminous bacterial hosts (12, 37), so functions that supply reduced flavin and precursors of the fatty aldehyde substrate are apparently not unique to the bioluminescence system.Light production by most species of luminous bacteria is strongly influenced by the density of the cell culture. Light emission per cell can be as much as 1,000-fold higher in dense cultures than in dilute cultures. Density-dependent regulation of luminescence has been investigated most thoroughly with the light organ symbiont Vibrio fischeri (9,25,33 luminescence. Autoinducer from V. fischeri has been shown to be N-(P-ketocaproyl)homoserine lactone (10). The genes (lux) necessary for light production in recombinant hosts have been cloned from V. fischeri (strain MJ-1) on one 9-kilobase (kb) fragment of DNA (12, 13). This fragment contains genes encoding regulatory functions and the luciferase and fatty acid reductase enzymes. Regulation of light production in recombinant Escherichia coli containing lux genes mirrored that observed in V. fischeri, so the refined genetic techniques developed for E. coli have been used to explore the molecular basis of luminescence control. It is clear from these studies that autoinducer controls light production by inducing transcription of the lux operon encoding the enzymes for luminescence.Expression of lux in Vibrio harveyi, as in V. fischeri, is dependent on the density of the cell culture, but the luminescence systems of these species differ substantially with respect to the nature of the autoinducer substances and the organization of lux genes. The autoinducer of V. fischeri, N-(,B-ketocaproyl)homoserine lactone, is produced only by V. fischeri and elicits a response only in V. fischeri. The autoinducer from V. harveyi is dif...