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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVED FORAGE AND BIOENERGY PLANTS AND TECHNOLOGIES FOR THE CENTRAL USA Title: Correlations between oxygen affinity and sequence classifications of plant hemoglobins

Authors
item Smagghe, Benoit - IOWA STATE UNIVERSITY
item Hoy, Julie - IOWA STATE UNIVERSITY
item Percifield, Ryan - UNIVERSITY OF GEORGIA
item Hargrove, Mark - IOWA STATE UNIVERSITY
item Sarath, Gautam
item Hilbert, Jean-Louis - UMRINRA FRANCE
item Watts, R - CSIRO AUSTRALIA
item Dennis, E - CSIRO AUSTRALIA
item Peacock, J - CSIRO AUSTRALIA
item Dewilde, S - UNIVERSITY OF ANTWERP
item Moens, L - UNIVERSITY OF ANTWERP
item Blouin, G - RICE UNIVERSITY
item Olson, J - RICE UNIVERSITY
item Appleby, C - EMERITUS CSIRO

Submitted to: Biopolymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 2, 2009
Publication Date: December 1, 2009
Repository URL: http://hdl.handle.net/10113/44295
Citation: Smagghe, B.J., Hoy, J., Percifield, R., Hargrove, M.S., Sarath, G., Hilbert, J., Watts, R., Dennis, E., Peacock, J., Dewilde, S., Moens, L., Blouin, G., Olson, J.S., Appleby, C.A. 2009. Correlations between oxygen affinity and sequence classifications of plant hemoglobins. Biopolymers. 91(12):1083-1096.

Interpretive Summary: Hemoglobins are ubiquitous oxygen-binding proteins. Plants contain three types of hemoglobins that differe in their oxygen-binding properties. In this work the oxygen-binding properties have been used along with protein sequence data to classify plant hemoglobins. Our data suggest that strong selective pressure has led to the evolution of plant hemoglobins to fulfill distinct physiological roles.

Technical Abstract: Plants express three phylogenetic classes of hemoglobins (Hb) based on sequence analyses. Class 1 and 2 Hbs are full length globins with the classical 8 helix Mb-like fold, whereas Class 3 plant Hbs resemble the truncated globins found in bacteria. With the exception of the specialized leghemoglobins, the physiological functions of these plant hemoglobins remain unknown. We have reviewed and, in some cases, measured new the oxygen binding properties of a large number of Class 1 and 2 plant non-symbiotic Hbs and leghemoglobins. We found that sequence classification also predicts distinct extents of hexacoordination with the distal histidine and markedly different overall oxygen affinities and association and dissociation rate constants. These results suggest strong selective pressure for the evolution of distinct physiological functions. The leghemoglobins evolved from the class 2 globins and show no hexacoordination, very high rates of O2 binding (~250 µM-1s-1), little electrostatic stabilization of bound ligands, moderately high rates of O2 dissociation (~5-15 s-1), and high oxygen affinity (P50 ˜ 50 nM). These properties both facilitate O2 diffusion to respiring, N2 fixing bacteria and reduce O2 tension in the root nodules of legumes. The class 1 plant Hbs show weak hexacoordination (KHisE7 ˜ 2), moderate rates of O2 binding (~25 µM-1s-1), very strong electrostatic stabilization of bound O2, very small rates of O2 dissociation (~0.16 s-1), and remarkably high O2 affinities (Kd or P50 ˜ 2 nM), suggesting a function involving O2 and NO scavenging. The class 2 Hbs exhibit strong hexacoordination (KHisE7 ˜ 100), low rates of O2 binding (~1 µM-1s-1), moderate electrostatic stabilization of bound O2, moderately low O2 dissociation rate constants (~1 s-1), and moderate, Mb-like O2 affinities (Kd or P50 ˜ 340 nM), perhaps suggesting a sensing role for sustained low, micromolar levels of oxygen.

Last Modified: 11/26/2014
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