AHNAK binds to S100A10–AnxA2 through a series of hydrogen bonds and hydrophobic interactions. (a) At the N-terminal end of the AHNAK peptide (yellow), the backbones of Gly1 and Val3 form hydrogen bonds to the main-chain atoms of Ser12 located at the C-terminal end of the AnxA2 peptide (chain D; purple). Hydrogen bonds are represented as dashed lines, while distances are shown for solid arrows. Weak electron density halfway between Asp84 of S100A10 (marine) and Lys2 of AHNAK suggests that a water molecule may act as a bridge between the two residues, but the model contains a nearby 2-propanol molecule whose methyl group would clash with the water O atom if modeled into the density (not shown). (b) A series of hydrophobic interactions are formed between Val3 and Phe5 of AHNAK (yellow), Leu13 of AnxA2 (chain D; purple) and Ile54, Leu74, Leu78 and Ala81 of S100A10 (chain A; marine). The main-chain carbonyl of Pro6 (AHNAK) accepts a hydrogen bond from the main-chain amide of Ala76 (S100A10, chain A). (c) The middle region of the peptide contains more hydrophobic residues which interact with hydrophobic pockets on S100A10. Met8 and Ile10 of AHNAK (yellow) face several hydrophobic residues near the S100A10 dimer interface (chain A, marine; chain B, dark blue). Additionally, the side-chain hydroxyl of Ser73 (S100A10, chain B) donates a hydrogen bond to the main-chain carbonyl of Lys9 (AHNAK). (d) The main chain of Thr14 (AHNAK; yellow) accepts and donates a hydrogen bond from Ser12 of AnxA2 (chain C; magenta). Additionally, the region contains hydrophobic interactions between Phe13 of AHNAK and several hydrophobic residues of S100A10 (chain B; dark blue) and Leu13 of AnxA2 (chain C). Lower-case letters represent chain IDs.