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Structure of magnesium-loaded ALG-2
Structural highlights
FunctionPDCD6_MOUSE Calcium-binding protein required for T-cell receptor-, Fas-, and glucocorticoid-induced cell death. Calcium-dependent adapter necessary for the association between PDCD6IP and TSG101 (By similarity). May mediate Ca(2+)-regulated signals along the death pathway. Interaction with DAPK1 can accelerate apoptotic cell death by increasing caspase-3 activity (By similarity). Publication Abstract from PubMedThe penta-EF-hand (PEF) protein ALG-2 (apoptosis-linked gene 2) has been implicated in several important physiological processes, including endoplasmic reticulum-Golgi vesicular transport and endosomal biogenesis/transport. ALG-2 was recently shown to harbor a metal ion-binding site with a high affinity for Mg2+ and a low affinity for Ca2+. We herein present the X-ray structure of Mg2+-bound ALG-2des23wt. Although the Calpha trace is nearly indistinguishable from that of the Ca2+-free protein, the orientation of the C-terminal helix differs in the two structures. Consistent with that observation, replacement of the +x ligand in EF5, D169, with alanine eliminates high-affinity Mg2+ binding. It also eliminates the low-affinity Ca2+ site and lowers the affinity of the remaining Ca2+-binding sites, EF3 and EF1. The coordination environment in EF5 approaches ideal Mg2+ octahedral geometry. The ligand array, consisting of three carboxylates (+x, +y, +z), a backbone carbonyl (-y), and two water molecules (-x, -z), may offer a recipe for a high-affinity, high-selectivity Mg2+-binding site. Sequence data for other PEF proteins indicate that select calpain large subunits, notably CAPN1 and CAPN8, may also possess a high-affinity Mg2+-binding site. In Mg2+-bound ALG-2, the carbonyl of F188 and the C-terminal carboxylate of V191 interact with the epsilon-ammonium group of K137 in the opposing subunit, suggesting that Mg2+ binding could have an impact on dimerization. Interestingly, EF1 and EF3 are also occupied in the crystal, despite having modest affinity for Mg2+. The results of a calorimetry-based analysis indicate that their Mg2+ binding constants are 2 orders of magnitude lower than that determined for EF5. EF5 Is the High-Affinity Mg2+ Site in ALG-2.,Tanner JJ, Frey BB, Pemberton T, Henzl MT Biochemistry. 2016 Aug 31. PMID:27541325[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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