Identification of trimethylation at C-terminal lysine of pilin in the cyanobacterium Synechocystis PCC 6803 |
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Authors: | Kim Young Hye Park Kyu Hwan Kim Se-Young Ji Eun Sun Kim Jin Young Lee Sang Kwang Yoo Jong Shin Kim Hyun Sik Park Young Mok |
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Affiliation: | aMass Spectrometry Research Center, Korea Basic Science Institute, Ochang 363-883, South Korea;bGraduate School of Analytical Science and Technology, Chungnam National University, Daejeon, 305-333, South Korea |
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Abstract: | 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 42 Da, 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. |
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Keywords: | Synechocystis sp. PCC 6803 Pilin Post-translational modification Trimethylation |
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