Adenylyl cyclase

Adenylyl Cyclase

Adenylyl cyclase (AC) is an enzyme with key regulatory roles in essentially all cells. It catalyzes the conversion of adenosine triphosphate (ATP) to cyclic adenosine monophosphate (cAMP) and pyrophosphate. cAMP is a crucial second messenger involved in signal transduction pathways, mediating the effects of hormones like glucagon and adrenaline.

Structure

Adenylyl cyclase is a membrane-bound enzyme that is typically composed of two transmembrane domains, each containing six membrane-spanning helices, and two cytoplasmic domains that form the catalytic core. The enzyme exists in multiple isoforms, each with distinct regulatory properties and tissue distributions.

Function

The primary function of adenylyl cyclase is to convert ATP to cAMP, which then acts as a second messenger to activate protein kinase A (PKA) and other downstream targets. This process is crucial for the regulation of various physiological processes, including metabolism, ion channel conductance, and gene transcription.

Regulation

Adenylyl cyclase activity is regulated by G protein-coupled receptors (GPCRs). When a ligand binds to a GPCR, it activates a G protein, which can either stimulate or inhibit adenylyl cyclase, depending on the type of G protein involved. For example, G_s proteins stimulate adenylyl cyclase, while G_i proteins inhibit it.

Isoforms

There are nine known isoforms of adenylyl cyclase in mammals, each with unique regulatory properties and tissue distributions. These isoforms are classified into four groups based on their regulatory characteristics:

• Group I: AC1, AC3, AC8 - Calcium/calmodulin-stimulated
• Group II: AC2, AC4, AC7 - G_s and G_i insensitive
• Group III: AC5, AC6 - Inhibited by calcium
• Group IV: AC9 - Distinct regulatory properties

Clinical Significance

Dysregulation of adenylyl cyclase activity is implicated in various diseases, including heart failure, depression, and certain types of cancer. Understanding the specific roles of different adenylyl cyclase isoforms in these conditions is an active area of research.

Related Pages

• Cyclic adenosine monophosphate
• G protein-coupled receptor
• Protein kinase A
• Signal transduction

Gallery

• Structure of adenylyl cyclase
  Structure of adenylyl cyclase
• Adenylate kinase
  Adenylate kinase
• Adenylyl cyclase diagram
  Adenylyl cyclase diagram
• Beta adrenergic receptor kinase
  Beta adrenergic receptor kinase