Secreted 3-isopropylmalate methyl ester signals invasive growth during amino acid starvation in Saccharomyces cerevisiae.
The Saccharomyces cerevisiae methyltransferase encoded by TMT1 catalyzes the AdoMet-dependent monomethylation of 3-isopropylmalate, an intermediate of the leucine biosynthetic pathway. The biological significance of methylating 3-isopropylmalate and the relationship between Tmt1 and the leucine biosynthetic pathway is not yet established. We present evidence here showing that methylation of 3-isopropylmalate functions to extracellularly signal yeast to grow invasively. We show that methyl esterification generates 3-isopropylmalate-1-methyl ester. We find that the Tmt1 methyltransferase functions independently of the biosynthetic pathway but is induced when cells are starved for amino acids; the largest induction is observed with the removal of leucine from the media. This amino acid starvation stress response is controlled by the transcriptional activator Gcn4. After methylation, 3-isopropylmalate methyl ester is secreted into the media within 3 h. Thin layer chromatography and gas chromatography mass spectroscopy confirm that the intact molecule is secreted. Finally, we show that purified 3-isopropylmalate methyl ester can enhance the ability of the haploid yeast strain 10560-23C to grow invasively. Our data identifies 3-isopropylmalate methyl ester as an autoinductive molecule that provides a signal to yeast to switch from vegetative to invasive growth in response to amino acid starvation.
Dumlao
Darren S
DS
Department of Chemistry and Biochemistry, and the Molecular Biology Institute, University of California, Los Angeles, California 90095-1569, USA.
Hertz
Nicholas
N
Clarke
Steven
S
D000596:Amino Acids / Q000172:deficiency*; D050976:Basic-Leucine Zipper Transcription Factors; D002384:Catalysis / Q000187:drug effects; D003470:Culture Media; D004268:DNA-Binding Proteins / Q000378:metabolism; D004790:Enzyme Induction / Q000187:drug effects; D004951:Esterification / Q000187:drug effects; D008401:Gas Chromatography-Mass Spectrometry; D007930:Leucine / Q000096:biosynthesis / Q000494:pharmacology; D008293:Malates / Q000737:chemistry / Q000378:metabolism*; D008780:Methyltransferases / Q000096:biosynthesis; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000378:metabolism
C526908:3-isopropylmalate methyl ester; D000596:Amino Acids; D050976:Basic-Leucine Zipper Transcription Factors; D003470:Culture Media; D004268:DNA-Binding Proteins; C501391:GCN4 protein, S cerevisiae; D008293:Malates; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C025313:beta-isopropylmalate; D008780:Methyltransferases; D007930:Leucine