PDBsum entry 6mjs

Electron transport

PDB id: 6mjs

Contents

Protein chains

128 a.a.

Ligands

REQ ×4

Metals

_CU ×4

Waters ×271

References listed in PDB file

Key reference

• Title: Two tryptophans are better than one in accelerating electron flow through a protein.
• Authors: K.Takematsu, H.R.Williamson, P.Nikolovski, J.T.Kaiser, Y.Sheng, P.Pospíšil, M.Towrie, J.Heyda, D.Hollas, S.Záliš, H.B.Gray, A.Vlček, J.R.Winkler.
• Ref.: ACS Cent Sci, 2019, 5, 192-200. [DOI no: 10.1021/acscentsci.8b00882]
• PubMed id: 30693338

Abstract

We have constructed and structurally characterized a Pseudomonas aeruginosa azurin mutant Re126WWCu^I , where two adjacent tryptophan residues (W124 and W122, indole separation 3.6-4.1 Å) are inserted between the Cu^I center and a Re photosensitizer coordinated to the imidazole of H126 (Re^I(H126)(CO)₃(4,7-dimethyl-1,10-phenanthroline)⁺). Cu^I oxidation by the photoexcited Re label (*Re) 22.9 Å away proceeds with a ∼70 ns time constant, similar to that of a single-tryptophan mutant (∼40 ns) with a 19.4 Å Re-Cu distance. Time-resolved spectroscopy (luminescence, visible and IR absorption) revealed two rapid reversible electron transfer steps, W124 → *Re (400-475 ps, K₁ ≅ 3.5-4) and W122 → W124^•+ (7-9 ns, K₂ ≅ 0.55-0.75), followed by a rate-determining (70-90 ns) Cu^I oxidation by W122^•+ ca. 11 Å away. The photocycle is completed by 120 μs recombination. No photochemical Cu^I oxidation was observed in Re126FWCu^I , whereas in Re126WFCu^I , the photocycle is restricted to the ReH126W124 unit and Cu^I remains isolated. QM/MM/MD simulations of Re126WWCu^I indicate that indole solvation changes through the hopping process and W124 → *Re electron transfer is accompanied by water fluctuations that tighten W124 solvation. Our finding that multistep tunneling (hopping) confers a ∼9000-fold advantage over single-step tunneling in the double-tryptophan protein supports the proposal that hole-hopping through tryptophan/tyrosine chains protects enzymes from oxidative damage.