A Hemoglobin from Plants Homologous to Truncated Hemoglobins of Microorganisms

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 98; no. 18; pp. 10119 - 10124
• Main Authors: Watts, R. A., Hunt, P. W., Hvitved, A. N., Hargrove, M. S., Peacock, W. J., Dennis, E. S.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 28.08.2001; National Acad Sciences; The National Academy of Sciences
• Subjects: Amino Acid Sequence; Amino acids; Animals; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis thaliana; Bacterial Proteins - genetics; Biochemistry; Biological Sciences; Eukaryota - genetics; Evolution; Flowers & plants; Gene Expression; Genes, Plant; GLB3 gene; GLB3 protein; Hemoglobin; Hemoglobins - genetics; Hemoglobins - metabolism; Introns; Kinetics; Ligands; Microorganisms; Molecular Sequence Data; Molecules; Photolysis; Phylogeny; Plant Proteins - genetics; Plant Proteins - metabolism; Plants; Plants - genetics; Proteins; Protozoan Proteins - genetics; RNA, Messenger - genetics; RNA, Plant - genetics; Sequence Homology, Amino Acid; Truncated Hemoglobins; Tuberculosis
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.191349198

We have identified a nuclear-encoded Hb from plants (GLB3) that has a central domain similar to the "truncated" Hbs of bacteria, protozoa, and algae. The three-dimensional structure of these Hbs is a 2-on-2 arrangement of α-helices, distinct from the 3-on-3 arrangement of the standard globin fold [Pesce, A., Couture, M., Dewilde, S., Guertin, M., Yamauchi, K., Ascenzi, P., Moens, L. & Bolognesi, M. (2000) EMBO J. 19, 2424-2434]. GLB3-like genes are not found in animals or yeast, but our analysis reveals that they are present in a wide range of Angiosperms and a Bryophyte. Although cyanobacteria and Chlamydomonas have 2-on-2 Hbs (GLBN), GLB3 is more likely related to GLBO-type 2-on-2 Hbs from bacteria. Consequently, GLB3 is unlikely to have arisen from a horizontal transfer between the chloroplast and nuclear genomes. Arabidopsis thaliana GLB3 protein exhibits unusual concentration-independent binding of O2and CO. The absorbance spectrum of deoxy-GLB3 is unique; the protein forms a transient six-coordinate structure after reduction and deoxygenation, which slowly converts to a five-coordinate structure. In A. thaliana, GLB3 is expressed throughout the plant but responds to none of the treatments that induce plant 3-on-3 Hbs. Our analysis of the sequence, ligand interactions, and expression profile of GLB3 indicates that this protein has unique biochemical properties, evolutionary history, and, most likely, a function distinct from those of other plant Hbs.