Identification of trimethylation at C-terminal lysine of pilin in the cyanobacterium Synechocystis PCC 6803.
Various post-translational modifications (PTMs) of pilin in Synechocystis sp. PCC 6803 have been proposed. In this study, we investigated previously unidentified PTMs of pilin by mass spectrometry (MS). MALDI-TOF MS and TOF/TOF MS showed that the molecular mass of the C-terminal lysine of pilin was increased by 42Da, which could represent acetylation (ΔM=42.0470) or trimethylation (ΔM=42.0106). To discriminate between these isobaric modifications, the molecular mass of the C-terminal tryptic peptide was measured using 15T Fourier transform ion cyclotron resonance (FT-ICR) MS. The high magnetic field FT-ICR provided sub-ppm mass accuracy, revealing that the C-terminal lysine was modified by trimethylation. We could also detect the existence of mono- and di-methylation of the C-terminal lysine. Cells expressing a pilin point mutant with glutamine replacing the C-terminal lysine showed dramatically reduced motility and short pili. These findings suggest that trimethylation of pilin at the C-terminal lysine may be essential for the biogenesis of functional pili.
Mass Spectrometry Research Center, Korea Basic Science Institute, Ochang 363-883, South Korea.
Young Hye
YH
Kim
Kyu Hwan
KH
Park
Se-Young
SY
Kim
Eun Sun
ES
Ji
Jin Young
JY
Kim
Sang Kwang
SK
Lee
Jong Shin
JS
Yoo
Hyun Sik
HS
Kim
Young Mok
YM
Park
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism*; D008239:Lysine / Q000235:genetics / Q000378:metabolism*; D008745:Methylation; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011499:Protein Processing, Post-Translational; D046939:Synechocystis / Q000378:metabolism*
D036781:Fimbriae Proteins; D008239:Lysine