A, primary basis for diversity of the AMPK heterotrimer. The ribbon diagram of a mammalian AMPK structure is from Protein Data Bank code 2Y94 (16). Sequence information refers to canonical UniProtKB entries for human AMPK polypeptides. aa, amino acids; AID, autoinhibitory domain; GBD, glycogen-binding domain; CBS, cystathionine β-synthase sequence. B, structure of the ActivX ATP probe designed to couple desthiobiotin to conserved Lys in the ATP-binding loop of a protein kinase.