A hemoglobin from plants homologous to truncated hemoglobins of microorganisms.
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 alpha-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 O(2) and 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.
Watts
R A
RA
CSIRO Plant Industry, Canberra, ACT 2601, Australia.
Hunt
P W
PW
Hvitved
A N
AN
Hargrove
M S
MS
Peacock
W J
WJ
Dennis
E S
ES
D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics; D056890:Eukaryota / Q000235:genetics; D015870:Gene Expression; D017343:Genes, Plant; D006454:Hemoglobins / Q000235:genetics* / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D010944:Plants / Q000235:genetics*; D015800:Protozoan Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D054793:Truncated Hemoglobins
D001426:Bacterial Proteins; D006454:Hemoglobins; D010940:Plant Proteins; D015800:Protozoan Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; D054793:Truncated Hemoglobins