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PDBsum entry 4twu
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Oxygen transport
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PDB id
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4twu
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References listed in PDB file
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Key reference
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Title
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Charge-Disproportionation symmetry breaking creates a heterodimeric myoglobin complex with enhanced affinity and rapid intracomplex electron transfer.
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Authors
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E.N.Trana,
J.M.Nocek,
J.V.Woude,
I.Span,
S.M.Smith,
A.C.Rosenzweig,
B.M.Hoffman.
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Ref.
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J Am Chem Soc, 2016,
138,
12615-12628.
[DOI no: ]
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PubMed id
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Abstract
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We report rapid photoinitiated intracomplex electron transfer (ET) within a
"charge-disproportionated" myoglobin (Mb) dimer with greatly enhanced
affinity. Two mutually supportive Brownian Dynamics (BD) interface redesign
strategies, one a new "heme-filtering" approach, were employed to
"break the symmetry" of a Mb homodimer by pairing Mb constructs with
complementary highly positive and highly negative net surface charges,
introduced through D/E → K and K → E mutations, respectively. BD simulations
using a previously developed positive mutant, Mb(+6) = Mb(D44K/D60K/E85K), led
to construction of the complementary negative mutant Mb(-6) = Mb(K45E, K63E,
K95E). Simulations predict the pair will form a well-defined complex comprising
a tight ensemble of conformations with nearly parallel hemes, at a metal-metal
distance ∼18-19 Å. Upon expression and X-ray characterization of the
partners, BD predictions were verified through ET photocycle measurements
enabled by Zn-deuteroporphyrin substitution, forming the [ZnMb(-6),
Fe(3+)Mb(+6)] complex. Triplet ET quenching shows charge disproportionation
increases the binding constant by no less than ∼5 orders of magnitude relative
to wild-type Mb values. All progress curves for charge separation (CS) and
charge recombination (CR) are reproduced by a generalized kinetic model for the
interprotein ET photocycle. The intracomplex ET rate constants for both CS and
CR are increased by over 5 orders of magnitude, and their viscosity independence
is indicative of true interprotein ET, rather than dynamic gating as seen in
previous studies. The complex displays an unprecedented timecourse for CR of the
CS intermediate I. After a laser flash, I forms through photoinduced CS,
accumulates to a maximum concentration, then dies away through CR. However,
before completely disappearing, I reappears without another flash and reaches a
second maximum before disappearing completely.
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