Figure 3.

Two views of a crystal structure of a partial heterotrimeric complex of mammalian AMPK¹⁶; the right-hand view is rotated about 180° about the y axis compared to the left-hand view. The constructs crystallized contained only the C-terminal domain of the β subunit and also lacked a flexible loop in the C-terminal domain of the α subunit. The α subunit AID was present but was not resolved in this crystal form; in the left-hand view, its approximate location would just to the right of the junction between the αsubunit C-lobe (green) and the α-linker (red). The crystals contained AMP bound at sites 3 and 4. Note how in this structure, access to the Thr172 site is restricted by the close association of the α-CTD with the kinase domain (left-hand view). In addition, note how AMP bound in site 3 is not visible because it is covered by the “α-hook” structure of the linker peptide (right-hand view, linker peptide in red). Key to acronyms: N-lobe, N-terminal lobe of kinase domain; C-lobe, C-terminal lobe of kinase domain; γ-NTD, N-terminal region of γ subunit; α-CTD, α subunit C-terminal domain; β-CTD, β subunit C-terminal domain; γ-CBS1-4, CBS repeats in γ subunit.