6D45

L89S Mutant of FeBMb Sperm Whale Myoglobin

Summary for 6D45

• Entry DOI: 10.2210/pdb6d45/pdb
• Descriptor: Myoglobin, PROTOPORPHYRIN IX CONTAINING FE (3 entities in total)
• Functional Keywords: nitric oxide reductase, nor, biosynthetic, hco, metal binding protein, oxygen storage
• Biological source: Physeter catodon (Sperm whale)
• Total number of polymer chains: 1
• Total formula weight: 17871.30

Authors

Bhagi-Damodaran, A.,Mirts, E.N.,Sandoval, B.,Lu, Y. (deposition date: 2018-04-17, release date: 2018-05-23, Last modification date: 2023-10-04)

Primary citation

Bhagi-Damodaran, A.,Reed, J.H.,Zhu, Q.,Shi, Y.,Hosseinzadeh, P.,Sandoval, B.A.,Harnden, K.A.,Wang, S.,Sponholtz, M.R.,Mirts, E.N.,Dwaraknath, S.,Zhang, Y.,Moenne-Loccoz, P.,Lu, Y.
Heme redox potentials hold the key to reactivity differences between nitric oxide reductase and heme-copper oxidase.
Proc. Natl. Acad. Sci. U.S.A., 115:6195-6200, 2018

PubMed 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 (FeMb) 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 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 FeMb(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.

PubMed: 29802230
DOI: 10.1073/pnas.1720298115

Experimental method

X-RAY DIFFRACTION (1.779 Å)