Beta subunit of AMP-activated protein kinase (AMPK), which is required for transcriptional, metabolic, and developmental adaptations in response to glucose limitation. Has a structural role, mediating heterotrimer formation, and a regulatory role, defining carbon source-regulated subcellular location and substrate specificity of the AMPK kinase complex. AMPK is a heterotrimer of an alpha catalytic subunit (ssp2), a beta (amk2) and a gamma non-catalytic subunits (cbs2). The beta subunit serves as a bridge between the catalytic and the regulatory subunit. Belongs to the 5'-AMP-activated protein kinase beta subunit family. Extended N-terminus.