Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Heterotrimeric G proteins, composed of alpha and betagamma subunits, forward signals from transmembrane receptors to intracellular effector enzymes and ion channels. Free betagamma activates downstream targets, but its action is terminated by association with GDP-liganded alpha subunits. Because alpha can inhibit activation of many effectors by betagamma, it is likely that the alpha subunit binding surfaces on betagamma overlap the surfaces necessary for effector activation. To test this hypothesis, we mutated residues on beta shown to contact alpha in the recently published crystal structures of the alphabetagamma heterotrimer (Wall, M. A., Coleman, D. E., Lee, E., Iniguez-Lluhi, J. A., Posner, B. A., Gilman, A. G., and Sprang, S. R. (1995) Cell 83, 1047-1058; Lambright, D. G., Sondek, J., Bohm, A., Skiba, N. P., Hamm, H. E., and Sigler, P. B. (1996) Nature 379, 311-319.). The alpha subunit binds to the flat, top surface of the toroidal beta subunit and also extends a helix along the side of the beta subunit at blade 1. We mutated four residues on the top surface of beta (Hbeta1[L117A], Hbeta1[D228R], Hbeta1[D246S], and Hbeta1[W332A]) and two residues on the side of beta that contacts alpha (Hbeta1[N88A/K89A]). Each of the mutant proteins was able to form beta gamma dimers, but they differed in their ability to bind alpha and to activate phospholipase C beta2 (PLCbeta2), PLCbeta3, and adenylyl cyclase II. Mutation of residues along the side of the torus at blade 1 diminish affinity for alpha but do not prevent activation of any of the effectors. Mutations on the alpha binding surface differentially affected PLCbeta2, PLCbeta3, and adenylyl cyclase II. Residues that affect PLCbeta and adenylyl cyclase II activity are found on opposite sides of the central tunnel, suggesting that PLC and adenylyl cyclase, like the alpha subunit, make many contacts on the top surface. None of the mutations affected the ability of betagamma to inhibit adenylyl cyclase I. We conclude that alpha, PLCbeta2, PLCbeta3, and adenylyl cyclase II share an interaction on the top surface of beta. The importance of individual residues is different for alpha binding and for effector activation and differs even between closely related isoforms of the same effector.
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PMID:Sites for Galpha binding on the G protein beta subunit overlap with sites for regulation of phospholipase Cbeta and adenylyl cyclase. 963 86

The effects of low concentrations of extracellular ATP on cytosolic Ca(2+), membrane potential, and transcription of IL-6 were studied in monocyte-derived human macrophages. During inflammation or infection many cells secrete ATP. We show here that application of 10 microM ATP or 10 microM UTP induces oscillations in cytosolic Ca(2+) with a frequency of approximately 12 min(-1) and oscillations in membrane potential. RT-PCR analysis showed expression of P2Y(1), P2Y(2), P2Y(11), P2X(1), P2X(4), and P2X(7) receptors, large-conductance (KCNMA1 and KCNMB1-4), and intermediate-conductance (KCNN4) Ca(2+)-activated K(+) channels. The Ca(2+)oscillations were unchanged after removal of extracellular Ca(2+), indicating that they were mainly due to movements of Ca(2+) between intracellular compartments. Comparison of the effects of different nucleotides suggests that the Ca(2+) oscillations were elicited by activation of P2Y(2) receptors coupled to phospholipase C. Patch-clamp experiments showed that ATP induced a transient depolarization, probably mediated by activation of P2X(4) receptors, followed by membrane potential oscillations due to opening of Ca(2+)-activated K(+) channels. We also found that 10 microM ATP gamma S increased transcription of IL-6 approximately 40-fold within 2 h. This effect was abolished by blockade of P2Y receptors with 100 microM suramin. Our results suggest that ATP released from inflamed, damaged, or metabolically impaired cells represents a "danger signal" that plays a major role in activating the innate immune system.
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PMID:Extracellular ATP induces oscillations of intracellular Ca2+ and membrane potential and promotes transcription of IL-6 in macrophages. 1519 22