An endosymbiont chaperonin is a novel type of histidine protein kinase.
Symbionin, a GroEL homologous molecular chaperone produced by an intracellular symbiont of the pea aphid, is able to transfer its high-energy phosphate bond to other compounds through its autophosphorylation. When the urea-dissociated monomeric symbionin fixed onto a polyvinylidene difluoride membrane was incubated with [gamma-32P] ATP, it was efficiently phosphorylated at elevated temperatures. The autophosphorylated monomeric 32P-labeled symbionin, when incubated with ADP, transferred a significant portion of its radioactivity to ADP, suggesting that the autocatalytically phosphorylated monomeric symbionin contains high-energy phosphate bonds. It was also shown that when symbiotic proteins were electrophoretically separated, blotted onto a polyvinylidene disulfide membrane and incubated with 32P-labeled symbionin, radioactivity was found on several kinds of polypeptides, indicating that the phosphoryl group was transferred from symbionin to other symbiotic proteins. Peptide sequence analysis and thin-layer chromatographic analysis of the 32P-labeled tryptic fragment of the phosphorylated symbionin revealed that the site of phosphorylation is His-133. These results suggested that symbionin functions as a histidine protein kinase, or a sensor molecule, of the two-component pathway known in other organisms. However, symbionin is not similar in amino acid sequence to any known histidine protein kinase.
Morioka
M
M
Zoological Institute, Graduate School of Science, University of Tokyo.
Muraoka
H
H
Yamamoto
K
K
Ishikawa
H
H
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001042:Aphids / Q000382:microbiology; D001426:Bacterial Proteins / Q000737:chemistry*; D001665:Binding Sites; D018833:Chaperonins / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry*; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation
D001426:Bacterial Proteins; D010761:Phosphorus Radioisotopes; C044322:SymL protein, Bacteria; D006639:Histidine; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D018833:Chaperonins