Prokaryotic calcium‐binding protein of the calmodulin superfamily Calcium binding to a Saccharopolyspora erythraea 20 kDa protein

Abstract

The EF-hand calcium-binding protein from Saccharopolyspora erythraea has been shown, using ¹¹³Cd NMR, to possess three Cd²⁺-ion binding sites. This indicates that of the four EF-hand motifs in the molecule, one (probably site 2) is unable to bind Cd²⁺-ions. Data from the titration of the protein with Ca²⁺, in the presence of Quin2, were fitted to a curve calculated on the assumption that the protein contains three high affinity Ca²⁺ binding sites, two of which (pK ₁ = 8.0. pK ₂ = 9.0) are strongly cooperative, and one single site (pK ₃ = 7.5). Preliminary ¹H NMR experiments indicate marked structural changes upon Ca²⁺-binding.