adenylate cyclase
American Heritage Dictionary:
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a·den·yl·ate cyclase
American Heritage Stedman's Medical Dictionary:
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adenylate cyclase
n.
An enzyme that catalyzes the formation of cyclic AMP from ATP. Also called 3',5'-cyclic AMP synthetase.
Oxford Dictionary of Biochemistry:
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adenylate cyclase
or adenylylcyclase or (incorrectly) adenyl cyclase
EC 4.6.1.1; systematic name: ATP pyrophosphate-lyase (cyclizing); a phosphorus-oxygen lyase enzyme that catalyses the elimination of diphosphate from adenosine 5′-triphosphate (ATP) to form adenosine 3′,5′-phosphate (cyclic AMP). It is an effector of signal transduction and other fundamental regulatory mechanisms, being regulated by some Gα subunits of G-proteins. In mammals it is a widely distributed membrane-bound glycoprotein with various isoforms (115 — 180 kDa). These are six-loop-six structures, the intracellular loop and the C-terminal domain being homologous to the guanylate cyclase catalytic domain. One of them bears an ATP-binding site. Type I, 1134 amino acids, is brain-specific, Ca2+/ calmodulin activated, and inhibited by G-protein βγ subunits. Types II (1088 amino acids) and IV (1064 amino acids) are calmodulin insensitive and activated by βγ subunits; type II is found in brain and olfactory tissue, type IV is widely distributed except in testis. Type III, from olfactory sensory neurons, is calmodulin sensitive and not regulated by βγ subunits. Types V and VI form a subgroup that is widely distributed and not stimulated by βγ subunits. Saccharomyces cerevisiae enzyme (2026 amino acids) has a weak structural relationship with the mammalian enzyme. It is positively regulated by the RAS1 and RAS2 gene products, but this property is not shared by a recombinant enzyme from Schizosaccharomyces pombe. A plant gene has been cloned, the deduced protein sequence having no similarity to prokaryotic counterparts, but showing striking similarity to the catalytic region of S. cerevisiae adenylate cyclase, and with the cytoplasmic domains of bovine adenylate cyclase and two mammalian guanylate cyclases. Soluble adenylate cyclases (abbr.: sAC) are not affected by G proteins but are activated by bicarbonate in kidney and choroid plexus. Some sACs are found in bacterial toxins.
EC 4.6.1.1; systematic name: ATP pyrophosphate-lyase (cyclizing); a phosphorus-oxygen lyase enzyme that catalyses the elimination of diphosphate from adenosine 5′-triphosphate (ATP) to form adenosine 3′,5′-phosphate (cyclic AMP). It is an effector of signal transduction and other fundamental regulatory mechanisms, being regulated by some Gα subunits of G-proteins. In mammals it is a widely distributed membrane-bound glycoprotein with various isoforms (115 — 180 kDa). These are six-loop-six structures, the intracellular loop and the C-terminal domain being homologous to the guanylate cyclase catalytic domain. One of them bears an ATP-binding site. Type I, 1134 amino acids, is brain-specific, Ca2+/ calmodulin activated, and inhibited by G-protein βγ subunits. Types II (1088 amino acids) and IV (1064 amino acids) are calmodulin insensitive and activated by βγ subunits; type II is found in brain and olfactory tissue, type IV is widely distributed except in testis. Type III, from olfactory sensory neurons, is calmodulin sensitive and not regulated by βγ subunits. Types V and VI form a subgroup that is widely distributed and not stimulated by βγ subunits. Saccharomyces cerevisiae enzyme (2026 amino acids) has a weak structural relationship with the mammalian enzyme. It is positively regulated by the RAS1 and RAS2 gene products, but this property is not shared by a recombinant enzyme from Schizosaccharomyces pombe. A plant gene has been cloned, the deduced protein sequence having no similarity to prokaryotic counterparts, but showing striking similarity to the catalytic region of S. cerevisiae adenylate cyclase, and with the cytoplasmic domains of bovine adenylate cyclase and two mammalian guanylate cyclases. Soluble adenylate cyclases (abbr.: sAC) are not affected by G proteins but are activated by bicarbonate in kidney and choroid plexus. Some sACs are found in bacterial toxins.
| adenylate, adenyl cyclase, adenyl | |
| adenylate deaminase, adenylate energy charge, adenylate isopentenyltransferase |
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Adenylate cyclase
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| Adenylate cyclase | |||||||
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| Identifiers | |||||||
| EC number | 4.6.1.1 | ||||||
| CAS number | 9012-42-4 | ||||||
| Databases | |||||||
| IntEnz | IntEnz view | ||||||
| BRENDA | BRENDA entry | ||||||
| ExPASy | NiceZyme view | ||||||
| KEGG | KEGG entry | ||||||
| MetaCyc | metabolic pathway | ||||||
| PRIAM | profile | ||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||
| Gene Ontology | AmiGO / EGO | ||||||
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Adenylate cyclase (EC 4.6.1.1, also known as adenylyl cyclase, adenyl cyclase or AC) is part of the G protein signaling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell (cytoplasm).
The outside signal binds to a receptor, which transmits a signal to the G protein, which transmits a signal to adenylate cyclase, which transmits a signal by converting adenosine triphosphate to cyclic adenosine monophosphate (cAMP). cAMP is known as a second messenger.[1]
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Contents
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Types
There are ten known adenylate cyclases in mammals:
Reaction
Adenylate cyclase catalyzes the conversion of ATP to 3',5'-cyclic AMP (cAMP) and pyrophosphate.
cAMP (cyclic adenosine monophosphate) is an important molecule in eukaryotic signal transduction, a so-called second messenger. Adenylate cyclase can be activated or inhibited by G proteins, which are coupled to membrane receptors and thus can respond to hormonal or other stimuli. Following activation of adenylate cyclase, the resulting cAMP acts as a second messenger by interacting with and regulating other proteins such as protein kinase A and cyclic nucleotide-gated ion channels.
Photoactivatable adenylate cyclase (PAC) was discovered in E. gracilis and can be expressed in other organisms through genetic manipulation. Shining blue light on a cell containing PAC activates it and abruptly increases the rate of conversion of ATP to cAMP. This is a useful technique for researchers in neuroscience because it allows them to quickly increase the intracellular cAMP levels in particular neurons, and to study the effect of that increase in neural activity on the behavior of the organism. For example, PAC expression in certain neurons has been shown to alter the grooming behavior in fruit flies exposed to blue light [1]. Researchers also use channelrhodopsin-2 in a similar fashion.
Structure
Adenylyl cyclase is a transmembrane protein. It passes through the plasma membrane twelve times.
The important parts for its function are located in the cytoplasm and can be subdivided into the N-terminus, C1a, C1b, C2a, and C2b.
The C1 region exists between transmembrane helices six and seven, and the C2 region follows transmembrane helix 12.
The C1a and C2a domains form a catalytic dimer where ATP binds and is converted to cAMP.
Regulation
Adenylate cyclase is dually regulated by G proteins (Gs stimulating activity and Gi inhibiting it), and by forskolin, as well as other class-specific substrates:
- Isoforms I, III and VIII are also stimulated by Ca2+/calmodulin.
- Isoforms V and VI are inhibited by Ca2+ in a calmodulin-independent manner.
- Isoforms II, IV and IX are stimulated by beta gamma subunits of the G protein.
- Isoforms I, V and VI are most clearly inhibited by Gi, while other isoforms show less dual regulation by the inhibitory G protein.
- Soluble AC (sAC) is not a transmembrane form and is not regulated by G proteins or forskolin, instead acts as a bicarbonate/pH sensor.
In neurons, calcium-sensitive adenylate cyclases are located next to calcium ion channels for faster reaction to Ca2+ influx; they are suspected of playing an important role in learning processes. This is supported by the fact that adenylate cyclases are coincidence detectors, meaning that they are activated only by several different signals occurring together. In peripheral cells and tissues adenylate cyclases appear to form molecular complexes with specific receptors and other signaling proteins in an isoform-specific manner.
Additional images
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Beta adrenergic receptor kinase pathway
References
- ^ Reece, Jane; Campbell, Neil (2002). Biology. San Francisco: Benjamin Cummings. pp. 207. ISBN 0-8053-6624-5.
- Sodeman W and Sodeman T (1985). "Physiologic- and Adenylate Cyclase-Coupled Beta-Adrenergic Receptors", "Pathologic Physiology Mechanisms of Disease",143-145.
External links
- MeSH Adenylate+cyclase
- Interactive 3D views of Adenylate cyclase at Proteopedia Adenylyl_cyclase
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American Heritage Dictionary
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
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American Heritage Stedman's Medical Dictionary
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company.
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Oxford Dictionary of Biochemistry
Oxford University Press. Oxford Dictionary of Biochemistry and Molecular Biology © 1997, 2000, 2006 All rights reserved.
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