cyclic AMP

cyclic AMP. Cyclic adenosine monophosphate, universally abbreviated as cAMP, is a pivotal second messenger crucial for intracellular signal transduction. Its discovery fundamentally transformed understanding of hormone action and cellular communication. This molecule mediates the effects of numerous extracellular signals, translating them into specific physiological responses within the cell.

Structure and properties

The molecule consists of an adenosine monophosphate with a phosphodiester bond linking the phosphate group to both the 3' and 5' positions of the ribose sugar, forming a characteristic cyclic structure. This unique ring conformation confers stability and specificity for binding to effector proteins like protein kinase A. Chemically, it is a derivative of adenosine triphosphate and is highly soluble in the aqueous cytosol. The structure was definitively elucidated through techniques like X-ray crystallography and nuclear magnetic resonance spectroscopy.

Biosynthesis and degradation

cAMP is synthesized from ATP by a family of enzymes known as adenylyl cyclase, which are often activated by G protein-coupled receptors upon binding of ligands such as epinephrine or glucagon. The activity of adenylyl cyclase is regulated by GTP-bound Gαs subunit proteins. Its concentration is tightly controlled by degradation via phosphodiesterase enzymes, which hydrolyze the 3'-phosphodiester bond to yield 5'-AMP. Key phosphodiesterase isoforms are targeted by drugs like caffeine and theophylline.

Biological functions

As a central second messenger, cAMP activates protein kinase A, which then phosphorylates a vast array of substrate proteins, altering their activity. This cascade regulates critical processes including glycogen metabolism in the liver, lipolysis in adipose tissue, and ion channel conductance in neurons. In bacteria, it functions in catabolite repression by binding to the catabolite activator protein. It also modulates gene expression in eukaryotes through transcription factors like CREB.

Role in disease

Dysregulation of cAMP signaling pathways is implicated in numerous pathologies. Overproduction is linked to disorders like cholera, where the Vibrio cholerae toxin persistently activates Gαs subunit. Deficiencies or mutations in components like the G protein or adenylyl cyclase are associated with conditions such as Albright's hereditary osteodystrophy. Altered phosphodiesterase activity is a factor in heart failure and inflammatory disease, making these enzymes targets for drugs like sildenafil and rolipram.

History and discovery

cAMP was discovered in 1958 by Earl Sutherland and his colleagues at Case Western Reserve University while investigating the mechanism of epinephrine action on glycogen breakdown in the liver. This seminal work, for which Earl Sutherland received the Nobel Prize in Physiology or Medicine in 1971, established the foundational concept of the second messenger. Subsequent research by Martin Rodbell and Alfred G. Gilman on G proteins, recognized with their own Nobel Prize, further detailed the upstream activation of adenylyl cyclase.

Category:Second messengers Category:Nucleotides Category:Cell signaling