Metalloproteins Diversified: The Auracyanins Are a Family of Cupredoxins That Stretch the Spectral and Redox Limits of Blue Copper Proteins

Abstract

The metal sites of electron transfer proteins are tuned for function. The type 1 copper site is one of the most utilized metal sites in electron transfer reactions. This site can be tuned by the protein environment from +80 mV to +680 mV in typical type 1 sites. Accompanying this huge variation in midpoint potentials are large changes in electronic structure, resulting in proteins that are blue, green, or even red. Here, we report a family of blue copper proteins, the auracyanins, from the filamentous anoxygenic phototroph Chloroflexus aurantiacus that display the entire known spectral and redox variations known in the type 1 copper site. C. aurantiacus encodes four auracyanins, labeled A-D. The midpoint potentials vary from +83 mV (auracyanin D) to +423 mV (auracyanin C). The electronic structures vary from classical blue copper UV-vis absorption spectra (auracyanin B) to highly perturbed spectra (auracyanins C and D). The spectrum of auracyanin C is temperature-dependent. The expansion and divergent nature of the auracyanins is a previously unseen phenomenon.

Spectroscopic Characterization of a Green Copper Site in a Single-Domain Cupredoxin

“…Color codes used for these diagrams are based on spectroscopic features (see Table S1 ) rather than reported visual colors. Abbreviations used: AcoP _A.f : Acidophile cytochrome c oxidase Partner from Acidithiobacillus ferrooxidans (current study); Ami _M.e : amicyanin from Methylobacterium extorquens [59] ; Aur C _C.a and Aur D _C.a : auracyanin C and D from Chloroflexus aurantiacus [48] ; Azu-1_ M.sp and Azu-2_ M.sp: azurin isoform 1 and 2 from Methylomonas sp. [59] ; Azu_ P.a: azurin from Pseudomonas aeruginosa [55] , [60] ; CBP_ Cu: cucumber basic protein from Cucumber [19] ; Lpc_ S.c: lipocyanin from Streptomyces coelicolor [61] ; Nir_ A.c: Nitrite reductase from Achromobacter cycloclastes [19] ; Nitroso_ N.e: nitrosocyanin from Nitrosomonas europaea [62] ; Paz_ Ac : pseudoazurin from Achromobacter cycloclastes [60] ; Plc_ Sp : plastocyanin from spinach [60] ; Rus _ A.f: rusticyanin from Acidithiobacillus ferrooxidans (current study) [34] ; Ste _Cu: stellacyanin from Cucumber [63] , [64] .…”

“…While several blue cupredoxins have been spectroscopically and functionally characterized, only a few natural members from the green and red color families have been studied so far. Very recently, two other single domain cupredoxins of unknown functions have been found in Chloroflexus aurantiacus : auracyanin C and D [48] . They have unusual colors (grey and light green, respectively), spectra and R L values.…”

Engineered holocytochrome c synthases that biosynthesize new cytochromes c

“…Spectroelectrochemistry was performed using a CHI620C CH Instruments potentiostat and a Shimadzu UV-1800 spectrophotometer as described previously (37). Measurements were carried out in 50 mM sodium phosphate buffer (pH 7.0) and 50 mM NaCl.…”

Dietary copper affects antioxidant and immune activity in hybrid tilapia (Oreochromis niloticus × Oreochromis aureus)

“…Dietary copper (Cu) is an important element for organism and functions as a cofactor in various redox enzymes (Chen & Chiba, ; Fulda, Voegelin, & Kretzschmar, ; King et al., ). The formation of deleterious free radicals is also enhanced by dietary Cu (Pekal, Biesaga, & Pyrzynska, ).…”