phosphothreonine and mocimycin

During protein synthesis, translation elongation factor Tu (Ef-Tu) is responsible for the selection and binding of the cognate aminoacyl-tRNA to the acceptor site on the ribosome. The activity of Ef-Tu is dependent on its interaction with GTP. Posttranslational modifications, such as phosphorylation, are known to regulate the activity of Ef-Tu in several prokaryotes. Although a study of the Mycobacterium tuberculosis phosphoproteome showed Ef-Tu to be phosphorylated, the role of phosphorylation in the regulation of Ef-Tu has not been studied. In this report, we show that phosphorylation of M. tuberculosis Ef-Tu (MtbEf-Tu) by PknB reduced its interaction with GTP, suggesting a concomitant reduction in the level of protein synthesis. Overexpression of PknB in Mycobacterium smegmatis indeed reduced the level of protein synthesis. MtbEf-Tu was found to be phosphorylated by PknB on multiple sites, including Thr118, which is required for optimal activity of the protein. We found that kirromycin, an Ef-Tu-specific antibiotic, had a significant effect on the nucleotide binding of unphosphorylated MtbEf-Tu but not on the phosphorylated protein. Our results show that the modulation of the MtbEf-Tu-GTP interaction by phosphorylation can have an impact on cellular protein synthesis and growth. These results also suggest that phosphorylation can change the sensitivity of the protein to the specific inhibitors. Thus, the efficacy of an inhibitor can also depend on the posttranslational modification(s) of the target and should be considered during the development of the molecule.

Topics: Electrophoresis, Gel, Two-Dimensional; Guanosine Triphosphate; Immunoblotting; Mycobacterium tuberculosis; Peptide Elongation Factor Tu; Phosphoproteins; Phosphorylation; Phosphothreonine; Protein Binding; Protein Serine-Threonine Kinases; Pyridones

We have cloned and sequenced the tuf1 gene from a kirromycin-producing strain of Streptomyces collinus. The gene encodes a polypeptide of 396 amino acid residues with a molecular weight of 43,849. The protein shows 97% identity with EF-Tu1 of S. coelicolor and is sensitive to kirromycin. EF-Tu-dependent translation of poly(U) was reduced to 50% in the presence of 0.25 microM kirromycin. Using high resolution two-dimensional electrophoresis and specific immunodetection with monoclonal antibodies we found that the EF-Tu1 is phosphorylated on threonine and that serine is the second phosphate-accepting amino acid. EF-Tu1 phosphorylated on threonine and serine residues was detected among the S150 supernatant proteins of vegetative cells, aerial mycelium and spores. The level of phosphorylated EF-Tu1 varied during the growth and differentiation.

Topics: Amino Acid Sequence; Base Sequence; DNA, Bacterial; Drug Resistance, Microbial; Electrophoresis, Polyacrylamide Gel; Escherichia coli; Immunosorbent Techniques; Isoelectric Focusing; Molecular Sequence Data; Peptide Elongation Factor Tu; Phosphorylation; Phosphoserine; Phosphothreonine; Pyridones; Sequence Analysis, DNA; Streptomyces