第１０３回自然環境論セミナー
Dynamic docking and inter-protein electron transfer
Prof. David N. Beratan
(R.J. Reynolds Professor of Chemistry, Duke University,
http://www.chem.duke.edu/)
日時：２００４年６月１４日（金）午後３時３０分−５時
場所：発達科学部 G３０２教室（G棟３階）
概要
Horse myoglobin (Mb) provides a convenient workbench for probing the
effects of electrostatics on binding and reactivity in the dynamic
[Mb, cytochrome b5] electron-transfer (ET) complex. We have combined
mutagenesis and heme neutralization to prepare a suite of six Mb
surface-charge variants: the Mb(S92D) and Mb(V67R) mutants introduce
additional charges on the front face; and incorporation of the heme
di-ester into each of these neutralizes the charge on the heme
propionates which further increases the positive charge on the front
face. For this set of mutants, the nominal charge of Mb changes by -1
to +3 units relative to native Mb. For each member of this set, we
have measured the bimolecular quenching rate constant (k2) for the
photoinitiated ET reaction as a function of ionic strength. We find:
i) a dramatic decoupling of binding and reactivity, in which the
bimolecular rate varies 1,000-fold within the suite of Mbs without a
significant change in binding affinity; ii) the ET reaction occurs
within the thermodynamic or rapid exchange limit of the dynamic-
docking model, as shown by the fact that the zero-ionic-strength bi-
molecular rate constant varies exponentially with the net charge on Mb;
iii) Brownian Dynamics docking profiles allow us to visualize the
microscopic basis of dynamic docking; iv) a new theoretical approach
which mathematically couples docking with reactivity (Functional
Docking) successfully describes changes of bimolecular ET rates upon
protein modification and the ionic strength variations.
連絡先：蛯名邦禎 (発達科学部自然環境論講座)
e-mail: ebina@kobe-u.ac.jp
voice: 078-803-7754
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