Protein Kinase, AMP-activated, alpha 1 Catalytic Subunit, EC=2.7.11.1

AMP-activated protein kinase (AMPK) is highly conserved from yeast to plants and animals and plays a key role in the regulation of energy homeostasis (1). AMPK is a heterotrimeric complex composed of a catalytic a subunit and regulatory b and y subunits, each of which is encoded by two or three distinct genes (a1, 2; B1, 2; y1, 2, 3) (2). The kinase is activated by an elevated AMP/ATP ratio due to cellular and environmental stress, such as heat shock, hypoxia and ischemia (1). The tumor suppressor LKB1, in association with accessory proteins STRAD and MO25, phosphorylates AMPKa at Thr172 in the activation loop and this phosphorylation is required for AMPK activation (3-5). AMPKa is also phosphorylated at Thr258 and Ser485 (for a1; Ser491 for a2). The upstream kinase and the biological significance of these phosphorylation events have yet to be elucidated (6). The B1 subunit is post-translationally modified by myristoylation and multisite phosphorylation including Ser24/25, Ser96, Ser101, Ser108 and Ser182 (6,7). Phosphorylation at Ser108 of the B1 subunit seems to be required for the activation of AMPK enzyme, while phosphorylation at Ser24/25 and Ser182 affects AMPK localization (7). Several mutations in AMPKy subunits have been identified, most of which are located in the putative AMP/ATP binding sites (CBS or Bateman domains). Mutations at these sites lead to reduction of AMPK activity and cause glycogen accumulation in heart or skeletal muscle (1,2). Accumulating evidence indicates that AMPK not only regulates the metabolism of fatty acids and glycogen, but also modulates protein synthesis and cell growth through EF2 and TSC2/mTOR pathways, as well as blood flow via eNOS/nNOS (1).