ALG-2 divalent-ion affinity: Calorimetric analysis of the des23 versions reveals high-affinity site for Mg2 +

•ALG-2des23wt binds Ca2 + ions sequentially, with no apparent cooperativity.•ALG-2des23ΔGF122 binds Ca2 + with evidence of inter-subunit cooperativity.•Both isoforms possess a high-affinity (K > 5 × 104 M− 1) binding-site for Mg2 +.•The high-affinity Mg2 + site exhibits atypically low affinity for Ca2 +.•The Mg2 +-binding site is believed to reside in the EF5 binding loop.

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