Hexa‐histidin tag position influences disulfide structure but not binding behavior of in vitro folded N‐terminal domain of rat corticotropin‐releasing factor receptor type 2a

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Abstract
The oxidative folding, particularly the arrangement of disulfide bonds of recombinant extracellular N‐terminal domains of the corticotropin‐releasing factor receptor type 2a bearing five cysteines (C2 to C6), was investigated. Depending on the position of a His‐tag, two types of disulfide patterns were found. In the case of an N‐terminal His‐tag, the disulfide bonds C2–C3 and C4–C6 were found, leaving C5 free, whereas the C‐terminal position of the His‐tag led to the disulfide pattern C2–C5 and C4–C6, and leaving C3 free. The latter pattern is consistent with the disulfide arrangement of the extracellular N‐terminal domain of the corticotropin‐releasing factor (CRF) receptor type 1, which has six cysteines (C1 to C6) and in which C1 is paired with C3. However, binding data of the two differently disulfide‐bridged domains show no significant differences in binding affinities to selected ligands, indicating the importance of the C‐terminal portion of the N‐terminal receptor domains, particularly the disulfide bond C4–C6 for ligand binding.