Abstract
The structural basis of the extreme pH dependence of oxygen binding to Root effect Hbs is a long-standing puzzle in the field of protein chemistry. A previously unappreciated role of steric factors in the Root effect was revealed by a comparison of pH effects on oxygenation and oxidation processes in human Hb relative to Spot (Leiostomus xanthurus) and Carp (Cyprinodon carpio) Hbs. The Root effect confers five-fold increased pH sensitivity to oxygenation of Spot and Carp Hbs relative to Hb A0 in the absence of anionic effectors, and even larger relative elevations of pH sensitivity of oxygenation in the presence of 0.2 M phosphate. Remarkably, the Root effect was not evident in the oxidation of the Root effect Hbs. This finding rules out pH-dependent alterations in the thermodynamic properties of the heme iron, measured in the anaerobic oxidation reaction, as the basis of the Root effect. The alternative explanation supported by these results is that the elevated pH sensitivity of oxygenation of Root effect Hbs is attributable to globin-dependent steric effects that alter oxygen affinity by constraining conformational fluidity, but which have little influence on electron exchange via the heme edge. This elegant mode of allosteric control can regulate oxygen affinity within a given quaternary state, in addition to modifying the T-R equilibrium. Evolution of Hb sequences that result in proton-linked steric barriers to heme oxygenation could provide a general mechanism to account for the appearance of the Root effect in the structurally diverse Hbs of many species.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1261-1268 |
| Number of pages | 8 |
| Journal | Biochimica et Biophysica Acta - Proteins and Proteomics |
| Volume | 1814 |
| Issue number | 10 |
| DOIs | |
| State | Published - Oct 2011 |
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Keywords
- Allostery
- Conformational fluidity
- Hemoglobin
- Redox potential
- Root effect
- Steric controls
ASJC Scopus subject areas
- Biochemistry
- Biophysics
- Analytical Chemistry
- Molecular Biology
Cite this
Steric factors moderate conformational fluidity and contribute to the high proton sensitivity of Root effect hemoglobins. / Bonaventura, Celia; Henkens, Robert; Friedman, Joel M.; Siburt, Claire J Parker; Kraiter, Daniel; Crumbliss, Alvin L.
In: Biochimica et Biophysica Acta - Proteins and Proteomics, Vol. 1814, No. 10, 10.2011, p. 1261-1268.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Steric factors moderate conformational fluidity and contribute to the high proton sensitivity of Root effect hemoglobins
AU - Bonaventura, Celia
AU - Henkens, Robert
AU - Friedman, Joel M.
AU - Siburt, Claire J Parker
AU - Kraiter, Daniel
AU - Crumbliss, Alvin L.
PY - 2011/10
Y1 - 2011/10
N2 - The structural basis of the extreme pH dependence of oxygen binding to Root effect Hbs is a long-standing puzzle in the field of protein chemistry. A previously unappreciated role of steric factors in the Root effect was revealed by a comparison of pH effects on oxygenation and oxidation processes in human Hb relative to Spot (Leiostomus xanthurus) and Carp (Cyprinodon carpio) Hbs. The Root effect confers five-fold increased pH sensitivity to oxygenation of Spot and Carp Hbs relative to Hb A0 in the absence of anionic effectors, and even larger relative elevations of pH sensitivity of oxygenation in the presence of 0.2 M phosphate. Remarkably, the Root effect was not evident in the oxidation of the Root effect Hbs. This finding rules out pH-dependent alterations in the thermodynamic properties of the heme iron, measured in the anaerobic oxidation reaction, as the basis of the Root effect. The alternative explanation supported by these results is that the elevated pH sensitivity of oxygenation of Root effect Hbs is attributable to globin-dependent steric effects that alter oxygen affinity by constraining conformational fluidity, but which have little influence on electron exchange via the heme edge. This elegant mode of allosteric control can regulate oxygen affinity within a given quaternary state, in addition to modifying the T-R equilibrium. Evolution of Hb sequences that result in proton-linked steric barriers to heme oxygenation could provide a general mechanism to account for the appearance of the Root effect in the structurally diverse Hbs of many species.
AB - The structural basis of the extreme pH dependence of oxygen binding to Root effect Hbs is a long-standing puzzle in the field of protein chemistry. A previously unappreciated role of steric factors in the Root effect was revealed by a comparison of pH effects on oxygenation and oxidation processes in human Hb relative to Spot (Leiostomus xanthurus) and Carp (Cyprinodon carpio) Hbs. The Root effect confers five-fold increased pH sensitivity to oxygenation of Spot and Carp Hbs relative to Hb A0 in the absence of anionic effectors, and even larger relative elevations of pH sensitivity of oxygenation in the presence of 0.2 M phosphate. Remarkably, the Root effect was not evident in the oxidation of the Root effect Hbs. This finding rules out pH-dependent alterations in the thermodynamic properties of the heme iron, measured in the anaerobic oxidation reaction, as the basis of the Root effect. The alternative explanation supported by these results is that the elevated pH sensitivity of oxygenation of Root effect Hbs is attributable to globin-dependent steric effects that alter oxygen affinity by constraining conformational fluidity, but which have little influence on electron exchange via the heme edge. This elegant mode of allosteric control can regulate oxygen affinity within a given quaternary state, in addition to modifying the T-R equilibrium. Evolution of Hb sequences that result in proton-linked steric barriers to heme oxygenation could provide a general mechanism to account for the appearance of the Root effect in the structurally diverse Hbs of many species.
KW - Allostery
KW - Conformational fluidity
KW - Hemoglobin
KW - Redox potential
KW - Root effect
KW - Steric controls
UR - http://www.scopus.com/inward/record.url?scp=79960556322&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=79960556322&partnerID=8YFLogxK
U2 - 10.1016/j.bbapap.2011.06.012
DO - 10.1016/j.bbapap.2011.06.012
M3 - Article
VL - 1814
SP - 1261
EP - 1268
JO - Biochimica et Biophysica Acta - Proteins and Proteomics
JF - Biochimica et Biophysica Acta - Proteins and Proteomics
SN - 1570-9639
IS - 10
ER -