A singular bacteriophytochrome acquired by lateral gene transfer.
Bacteriophytochromes are phytochrome-like proteins that mediate photosensory responses in various bacteria according to their light environment. The genome of the photosynthetic and plant-symbiotic Bradyrhizobium sp. strain ORS278 revealed the presence of a genomic island acquired by lateral transfer harboring a bacteriophytochrome gene, BrBphP3.ORS278, and genes involved in the synthesis of phycocyanobilin and gas vesicles. The corresponding protein BrBphP3.ORS278 is phylogenetically distant from the other (bacterio)phytochromes described thus far and displays a series of unusual properties. It binds phycocyanobilin as a chromophore, a unique feature for a bacteriophytochrome. Moreover, its C-terminal region is short and displays no homology with any known functional domain. Its dark-adapted state absorbs maximally around 610 nm, an unusually short wavelength for (bacterio)phytochromes. This form is designated as Po for orange-absorbing form. Upon illumination, a photo-reversible switch occurs between the Po form and a red (670 nm)-absorbing form (Pr), which rapidly backreacts in the dark. Because of this instability, illumination results in a mixture of the Po and Pr states in proportions that depend on the intensity. These uncommon features suggest that BrBphP3.ORS278 could be fitted to measure light intensity rather than color.
Jaubert
Marianne
M
Laboratoire des Symbioses Tropicales et Méditerranéennes, Campus de Baillarguet, 34398 Montpellier, France.
Lavergne
Jérôme
J
Fardoux
Joël
J
Hannibal
Laure
L
Vuillet
Laurie
L
Adriano
Jean-Marc
JM
Bouyer
Pierre
P
Pignol
David
D
Giraud
Eric
E
Verméglio
André
A
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D020369:Bradyrhizobium / Q000235:genetics*; D005453:Fluorescence; D022761:Gene Transfer, Horizontal; D008969:Molecular Sequence Data; D052980:Phycobilins / Q000378:metabolism; D010798:Phycocyanin / Q000378:metabolism; D010834:Phytochrome / Q000737:chemistry / Q000235:genetics*; D013696:Temperature
D001426:Bacterial Proteins; D052980:Phycobilins; D010798:Phycocyanin; D010834:Phytochrome; C011069:phycocyanobilin