Phosphorylation of LHI beta during membrane synthesis in the photosynthetic bacterium Rhodovulum sulfidophilum.
Cells of Rhv. sulfidophilum were grown under different conditions in the presence of 32P-phosphate and the corresponding H and L membrane fractions obtained and fractionated by SDS-PAGE. Both membranes showed almost identical polypeptide composition. The bacteriochlorophyll (Bchl) specific content in H was always lower that in L. As described before, oxygen did not regulate gene expression. Under high light, an almost two- to threefold decrease of the cellular specific Bchl content was observed. Pulse and chase experiments showed that transitions from aerobiosis to light-anaerobiosis did not quantitatively affect the Bchl content of the membranes, although a turnover of the 32P-phosphate and 35S-methionine was observed. LHI beta was the only polypeptidic subunit of the Bchl-binding polypeptides that was phosphorylated in vivo, and phosphotyrosine was the only phosphorylated amino acid detectable. The phosphorylated LHI beta was determined to be insoluble in the organic solvent mixture of (vol/vol) 1:1 chloroform-methanol containing ammonium acetate (0.1 m final concentration). Treatment with a chaotropic agent such as Na2CO3 solubilized the phosphorylated LHI beta, indicating that part of this posttranslationally modified polypeptide was not inserted in a transmembrane position. These results were used to speculate about the regulatory properties of this posttranslational modification of LHI beta on membrane differentiation.
Iustman
L J
LJ
Cátedra de Microbiología, Facultad de Agronomía, (UBA) and Instituto de Investigaciones Bioquímicas y Fisiológicas (IByF-CONICET), Av. San Martín 4453, 1417 Capital Federal, Argentina.
Pucheu
N L
NL
Kerber
N L
NL
Vandekerckhove
J
J
Tadros
M H
MH
Garcia
A F
AF
D020561:Alphaproteobacteria / Q000254:growth & development / Q000378:metabolism*; D001426:Bacterial Proteins; D001429:Bacteriochlorophylls / Q000378:metabolism; D002254:Carbonates / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D015964:Gene Expression Regulation, Bacterial; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010766:Phosphorylation; D010788:Photosynthesis / Q000502:physiology; D045322:Photosynthetic Reaction Center Complex Proteins / Q000302:isolation & purification / Q000378:metabolism*
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D002254:Carbonates; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; C094744:light-harvesting complex 1, Rhodospirillum; C005686:sodium carbonate