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MtnK, methylthioribose kinase, is a starvation-induced protein in Bacillus subtilis
A Sekowska1, L Mulard, S Krogh
1HKU-Pasteur Research Centre, Dexter HC Man Building, Sassoon Road, Pokfulam, Hong Kong, China. sekowska@hkucc.hku.hk
Background:
Methylthioadenosine, the main by-product of spermidine synthesis, is degraded in Bacillus subtilis as adenine and methylthioribose. The latter is an excellent sulfur source and the precursor of quorum-sensing signalling molecules. Nothing was known about methylthioribose recycling in this organism.
Results:
Using trifluoromethylthioribose as a toxic analog to select for resistant mutants, we demonstrate that methylthioribose is first phosphorylated by MtnK, methylthioribose kinase, the product of gene mtnK (formerly ykrT), expressed as an operon with mtnS (formerly ykrS) in an abundant transcript with a S-box leader sequence. Although participating in methylthioribose recycling, the function of mtnS remained elusive. We also show that MtnK synthesis is boosted under starvation condition, in the following decreasing order: carbon-, sulfur- and nitrogen-starvation. We finally show that this enzyme is part of the family Pfam 01633 (choline kinases) which belongs to a large cluster of orthologs comprizing antibiotic aminoglycoside kinases and protein serine/threonine kinases.
Conclusions:
The first step of methylthioribose recycling is phosphorylation by MTR kinase, coded by the mtnK (formerly ykrT) gene. Analysis of the neighbourhood of mtnK demonstrates that genes located in its immediate vicinity (now named mtnUVWXYZ, formerly ykrUVWXYZ) are also required for methylthioribose recycling.
Insights
Methylthioribose recycling in Bacillus subtilis begins with phosphorylation by MtnK (methylthioribose kinase). Additional genes, mtnUVWXYZ, are also essential for this crucial metabolic pathway.
Area of Science:
- Microbiology
- Biochemistry
- Molecular Biology
Background:
- Methylthioadenosine is a key spermidine synthesis byproduct in Bacillus subtilis.
- Methylthioribose, a degradation product, serves as a sulfur source and quorum-sensing precursor.
- The metabolic fate of methylthioribose in B. subtilis was previously unknown.
Purpose of the Study:
- To elucidate the mechanism of methylthioribose recycling in Bacillus subtilis.
- To identify the genes and enzymes involved in methylthioribose metabolism.
- To understand the regulation of methylthioribose recycling under different conditions.
Main Methods:
- Selection of trifluoromethylthioribose-resistant mutants.
- Gene expression analysis (operon structure, S-box leader).
- Bioinformatic analysis (Pfam database, ortholog clusters).
Main Results:
- Identified MtnK (methylthioribose kinase) as the enzyme catalyzing the first step of methylthioribose recycling.
- Demonstrated that mtnK is co-transcribed with mtnS in an abundant transcript.
- Showed increased MtnK synthesis under carbon, sulfur, and nitrogen starvation.
- Revealed that mtnK belongs to the choline kinase family (Pfam 01633).
- Identified additional genes (mtnUVWXYZ) essential for methylthioribose recycling.
Conclusions:
- Phosphorylation by MtnK is the initial step in methylthioribose recycling.
- The mtnK gene (formerly ykrT) encodes MtnK.
- Genes mtnUVWXYZ (formerly ykrUVWXYZ) are also critical for methylthioribose recycling.