Two histidines are involved in the coordination sphere of all type 1 blue copper proteins that play critical roles in long-range electron transfer of a wide range of biological processes from photosynthesis to respiration. Previous studies in probing the role of the histidines replaced the histidines with natural amino acids that often perturbed many factors such as electronic and steric properties at the same time, making it difficult to pinpoint the exact role of the histidine. Here we used expressed protein ligation to replace one of the equatorial histidines with its  isostructural analogues.  Electronic absorption and electron paramagnetic resonance spectra of these variants indicated minimal perturbation of the metal-binding site. On the other hand, the reduction potential of these protein varied significantly from wild type, showing a positive correlation with acid dissociation constant of heterocycle on equatorial histidine position.

Reduction potential tuning
of blue copper protein by introducing histidine analog at equatorial position

242nd National Meeting (2011)

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Reduction potential tuning of blue copper protein by introducing histidine analog at equatorial position