Skip to main content
Journal cover image

Dynamic docking and electron transfer between Zn-myoglobin and cytochrome b(5).

Publication ,  Journal Article
Liang, Z-X; Nocek, JM; Huang, K; Hayes, RT; Kurnikov, IV; Beratan, DN; Hoffman, BM
Published in: Journal of the American Chemical Society
June 2002

We present a broad study of the effect of neutralizing the two negative charges of the Mb propionates on the interaction and electron transfer (ET) between horse Mb and bovine cyt b(5), through use of Zn-substituted Mb (ZnMb, 1) to study the photoinitiated reaction, ((3)ZnP)Mb + Fe(3+)cyt b(5) --> (ZnP)(+)Mb + Fe(2+)cyt b(5). The charge neutralization has been carried out both by replacing the Mb heme with zinc-deuteroporphyrin dimethylester (ZnMb(dme), 2), which replaces the charges by small neutral hydrophobic patches, and also by replacement with the newly prepared zinc-deuteroporphyrin diamide (ZnMb(diamide), 3), which converts the charged groups to neutral, hydrophilic ones. The effect of propionate neutralization on the conformation of the zinc-porphyrin in the Mb heme pocket has been studied by multinuclear NMR with an (15)N labeled zinc porphyrin derivative (ZnMb((15)N-diamide), 4). The rates of photoinitiated ET between the Mb's (1-3) and cyt b(5) have been measured over a range of pH values and ionic strengths. Isothermal titration calorimetry (ITC) and NMR methods have been used to independently investigate the effect of charge neutralization on Mb/b(5) binding. The neutralization of the two heme propionates of ZnMb by formation of the heme diester or, for the first time, the diamide increases the second-order rate constant of the ET reaction between ZnMb and cyt b(5) by as much as several 100-fold, depending on pH and ionic strength, while causing negligible changes in binding affinity. Brownian dynamic (BD) simulations and ET pathway calculations provide insight into the protein docking and ET process. The results support a new "dynamic docking" paradigm for protein-protein reactions in which numerous weakly bound conformations of the docked complex contribute to the binding of cyt b(5) to Mb and Hb, but only a very small subset of these are ET active, and this subset does not include the conformations most favorable for binding; the Mb surface is a large "target" with a small "bullseye" for the cyt b(5) "arrow". This paradigm differs sharply from the more familiar, "simple" docking within a single, or narrow range of conformations, where binding strength and ET reactivity increase in parallel. Likewise, it is distinct from, although complementary to, the well-known picture of conformational control of ET through "gating", or a related picture of "conformational coupling". The new model describes situations in which tight binding does not correlate with efficient ET reactivity, and explains how it is possible to modulate reactivity without changing affinity. Such "decoupling" of reactivity from binding clearly is of physiological relevance for the reduction of met-Mb in muscle and of met-Hb in a red cell, where tight binding of cyt b(5) to the high concentration of ferrous-Mb/Hb would prevent the cytochrome from finding and reducing the oxidized proteins; it likely is of physiological relevance in other situations, as well.

Duke Scholars

Published In

Journal of the American Chemical Society

DOI

EISSN

1520-5126

ISSN

0002-7863

Publication Date

June 2002

Volume

124

Issue

24

Start / End Page

6849 / 6859

Related Subject Headings

  • Zinc
  • Protein Conformation
  • Nuclear Magnetic Resonance, Biomolecular
  • Myoglobin
  • Metalloporphyrins
  • Kinetics
  • Horses
  • General Chemistry
  • Electrons
  • Cytochromes b5
 

Citation

APA
Chicago
ICMJE
MLA
NLM
Liang, Z.-X., Nocek, J. M., Huang, K., Hayes, R. T., Kurnikov, I. V., Beratan, D. N., & Hoffman, B. M. (2002). Dynamic docking and electron transfer between Zn-myoglobin and cytochrome b(5). Journal of the American Chemical Society, 124(24), 6849–6859. https://doi.org/10.1021/ja0127032
Liang, Zhao-Xun, Judith M. Nocek, Kai Huang, Ryan T. Hayes, Igor V. Kurnikov, David N. Beratan, and Brian M. Hoffman. “Dynamic docking and electron transfer between Zn-myoglobin and cytochrome b(5).Journal of the American Chemical Society 124, no. 24 (June 2002): 6849–59. https://doi.org/10.1021/ja0127032.
Liang Z-X, Nocek JM, Huang K, Hayes RT, Kurnikov IV, Beratan DN, et al. Dynamic docking and electron transfer between Zn-myoglobin and cytochrome b(5). Journal of the American Chemical Society. 2002 Jun;124(24):6849–59.
Liang, Zhao-Xun, et al. “Dynamic docking and electron transfer between Zn-myoglobin and cytochrome b(5).Journal of the American Chemical Society, vol. 124, no. 24, June 2002, pp. 6849–59. Epmc, doi:10.1021/ja0127032.
Liang Z-X, Nocek JM, Huang K, Hayes RT, Kurnikov IV, Beratan DN, Hoffman BM. Dynamic docking and electron transfer between Zn-myoglobin and cytochrome b(5). Journal of the American Chemical Society. 2002 Jun;124(24):6849–6859.
Journal cover image

Published In

Journal of the American Chemical Society

DOI

EISSN

1520-5126

ISSN

0002-7863

Publication Date

June 2002

Volume

124

Issue

24

Start / End Page

6849 / 6859

Related Subject Headings

  • Zinc
  • Protein Conformation
  • Nuclear Magnetic Resonance, Biomolecular
  • Myoglobin
  • Metalloporphyrins
  • Kinetics
  • Horses
  • General Chemistry
  • Electrons
  • Cytochromes b5