Ligand binding and hexacoordination in synechocystis hemoglobin

A large and phylogenetically diverse group of organisms contain truncated hemoglobins, including the unicellular cyanobacterium Synechocystis (Pesce, A., Couture, M., Dewilde, S., Guertin, M., Yamauchi, K., Ascenzi, P., Moens, L., and Bolognesi, M. (2000) EMBO J. 19, 2424-2434). Synechocystis hemogl...

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Bibliographic Details
Published in:The Journal of biological chemistry 2001-09, Vol.276 (37), p.34714-34721
Main Authors: Hvitved, A N, Trent, 3rd, J T, Premer, S A, Hargrove, M S
Format: Article
Language:English
Subjects:
Carbon Monoxide - metabolism
Cyanobacteria - chemistry
Cyanophyta
Hemoglobins - chemistry
Hemoglobins - metabolism
hexacoordination
Ligands
Oxygen - metabolism
Structure-Activity Relationship
Synechocystis
Truncated Hemoglobins
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Summary:A large and phylogenetically diverse group of organisms contain truncated hemoglobins, including the unicellular cyanobacterium Synechocystis (Pesce, A., Couture, M., Dewilde, S., Guertin, M., Yamauchi, K., Ascenzi, P., Moens, L., and Bolognesi, M. (2000) EMBO J. 19, 2424-2434). Synechocystis hemoglobin is also hexacoordinate, with a heme pocket histidine that reversibly coordinates the ligand binding site. Hexacoordinate hemoglobins are ubiquitous in plants and are now being identified in a diverse array of organisms including humans (Arredondo-Peter, R., Hargrove, M. S., Moran, J. F., Sarath, G., and Klucas, R. V. (1998) Plant Physiol. 118, 1121-1125; Trent, J. T., III, Watts, R. A., and Hargrove, M. S. (2001) J. Biol. Chem. 276, 30106-30110). Rate constants for association and dissociation of the hexacoordinating amino acid side chain in Synechocystis hemoglobin have been measured along with bimolecular rate constants for association of oxygen and carbon monoxide following laser flash photolysis. These values were compared with ligand binding initiated by rapid mixing. Site-directed mutagenesis was used to determine the roles of several heme pocket amino acids in facilitating hexacoordination and stabilizing bound oxygen. It is demonstrated that Synechocystis hemoglobin contains a very reactive binding site and that ligand migration through the protein is rapid. Rate constants for hexacoordination by His(46) are also large and facilitated by other heme pocket amino acids including Gln(43).
ISSN:0021-9258
DOI:10.1074/jbc.M105175200