IglG is a metal-binding PAAR-like protein.

(A) Metal content of purified GST-IglG or GST proteins was determined by ICP-MS. Values for Iron (Fe), Zinc (Zn), Copper (Cu) and Nickel (Ni) are shown. Box and whiskers (Min to Max) are shown with each point representing the metal to protein ratio for independent protein expression and purification processes (n = 5). (B) Metal content of purified GST-IglG or the indicated GST-IglG cysteine mutant proteins was determined by ICP-MS. The metal content (iron plus zinc) of each GST-IglG cysteine mutant was normalized to the metal content of the GST-IglG protein expressed and purified at the same time. (C) Purified His₆-IglG protein is shown by coomassie blue staining (lane 3) after purification under denaturing conditions and refolding by step-wise dialysis. Whole cell lysates before (lane 1) and after IPTG induction (lane 2) are shown. (D, E) The conformation of His₆-IglG protein refolded in the presence of EDTA was analyzed by circular dichroism spectroscopy upon addition of increasing concentrations of FeSO₄ and ZnSO₄ (D), or increasing concentrations of TCEP (E) to reduce the potential disulfide bonds (concentrations are expressed as molar equivalent).