ADRB2 (adrenoceptor beta 2, surface)

Description	β2 adrenergic receptor is a member of the superfamily of G-protein coupled receptors (GPCRs) (McGraw and Liggett, 2005; Johnson, 2006). The receptor is comprised of 413 amino acid residues of approximately 46500 daltons (Johnson, 2006). β2 adrenergic receptor is N-glycosylated at amino acids 6, 15, and 187; these are important for roper insertion of the receptor into the membrane as well as for agonist trafficking (McGraw and Liggett, 2005; Johnson, 2006).
Expression	β2 adrenergic receptor is widely distributed, this protein is expressed by airway smooth muscle (30-40000 per cell), epithelial and endothelial cells of the lung, smooth muscle of blood vessels, skeletal muscle, mast cells, lymphocytes, oral and skin keratinocytes and also by diverse cancer cells (Kohm and Sanders, 2001; Lutgendorf et al., 2003; Johnson, 2006; Sood et al., 2006; Thaker et al., 2006; Yang et al., 2006; Sastry et al., 2007; Yu et al., 2007; Liu et al., 2008a; Liu et al., 2008b; Shang et al., 2009; Sivamani et al., 2009; Yang et al., 2009; Bernabé et al., 2011; Bravo-Calderón et al., 2011-2012; Steenhuis et al., 2011; Zhang et al., 2011; Loenneke et al., 2012).
Localisation	β2 adrenergic receptor is a transmembrane protein. Like all GPCRs, the β2 adrenergic receptor has seven transmembrane a domains that form a pocket containing binding sites for agonists and competitive antagonists (McGraw and Liggett, 2005; Johnson, 2006). There are 3 extracellular loops, with one being the amino terminus, and 3 intracellular loops, with a carboxy terminus (McGraw and Liggett, 2005; Johnson, 2006).
Function	Agonist binding of β2 adrenergic receptor results in activation of Gs protein. The Gs protein a subunit stimulates adenylyl cyclase to generate cyclic 3'-5'-adenosine monophosphate (cAMP), which in sequence activates the cAMP-dependent protein kinase A (PKA) and the agonist-occupied receptor is phosphorylated. After phosphorylation, the receptor switches its coupling specificity to Gi. GTP-bound Giα dissociates from the heterodimeric Gβγ, and free Gβγ subunits mediate activation of the MAP kinase signaling pathway in the same way as Gi-coupled receptors. Increase of intracellular cAMP levels leads diverse cell functions as cell proliferation, differentiation, angiogenesis and migration (Daaka et al., 1997).
	Activation of protein kinase A (PKA) by signal transduction of β2 adrenergic receptor (adapted of Rosenbaum et al., 2009).

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