In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 115, No. 24 ( 2018-06-12), p. 6195-6200
Abstract:
Despite high structural homology between NO reductases (NORs) and heme-copper oxidases (HCOs), factors governing their reaction specificity remain to be understood. Using a myoglobin-based model of NOR (Fe B Mb) and tuning its heme redox potentials (E°′) to cover the native NOR range, through manipulating hydrogen bonding to the proximal histidine ligand and replacing heme b with monoformyl (MF-) or diformyl (DF-) hemes, we herein demonstrate that the E°′ holds the key to reactivity differences between NOR and HCO. Detailed electrochemical, kinetic, and vibrational spectroscopic studies, in tandem with density functional theory calculations, demonstrate a strong influence of heme E°′ on NO reduction. Decreasing E°′ from +148 to −130 mV significantly impacts electronic properties of the NOR mimics, resulting in 180- and 633-fold enhancements in NO association and heme-nitrosyl decay rates, respectively. Our results indicate that NORs exhibit finely tuned E°′ that maximizes their enzymatic efficiency and helps achieve a balance between opposite factors: fast NO binding and decay of dinitrosyl species facilitated by low E°′ and fast electron transfer facilitated by high E°′. Only when E°′ is optimally tuned in Fe B Mb(MF-heme) for NO binding, heme-nitrosyl decay, and electron transfer does the protein achieve multiple ( 〉 35) turnovers, previously not achieved by synthetic or enzyme-based NOR models. This also explains a long-standing question in bioenergetics of selective cross-reactivity in HCOs. Only HCOs with heme E°′ in a similar range as NORs (between −59 and 200 mV) exhibit NOR reactivity. Thus, our work demonstrates efficient tuning of E°′ in various metalloproteins for their optimal functionality.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.1720298115
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2018
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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