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The modular organization of multifunctional peptide synthetases
J Vater1, T Stein, D Vollenbroich
1Max-Volmer-Institut für Biophysikalische Chemie und Biochemie, Technische Universität Berlin, Germany. jovajceh@mailszrz_zrz_TU-Berlin.DE
Journal of Protein Chemistry
|July 1, 1997
Summary
Gramicidin S synthetase 2 was labeled to identify a peptide fragment crucial for nonribosomal peptide biosynthesis. This research supports the "Multiple Carrier Model" for synthesizing complex peptides.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- Nonribosomal peptide synthetases (NPSs) are large modular enzymes responsible for synthesizing a diverse array of bioactive peptides.
- Understanding the catalytic mechanisms and functional roles of conserved residues within NPS modules is essential for elucidating peptide biosynthesis pathways.
Purpose of the Study:
- To identify and characterize the valine thiolation center of Gramicidin S synthetase 2.
- To investigate the function of conserved amino acid residues in thiolation, elongation, and epimerization motifs of surfactin synthetase.
- To discuss the modular structure of multifunctional peptide synthetases.
Main Methods:
- Affinity labeling of Gramicidin S synthetase 2 with N-[3H]ethylmaleimide.
- Tryptic digestion and purification of radioactive peptide fragments using reversed-phase High-Performance Liquid Chromatography (HPLC).
- Identification of the peptide fragment using liquid-phase N-terminal sequencing and Electrospray Ionization Mass Spectrometry (ESI-MS).
- Site-specific mutagenesis of surfactin synthetase modules.
Main Results:
- A radioactive hexadecapeptide fragment containing the thiolation motif LGG(H/D)S(L/I) was isolated and identified.
- A 4'-phosphopantetheine cofactor was found attached to the reactive serine of the isolated peptide fragment.
- Mutagenesis studies provided insights into the roles of conserved residues in peptide biosynthesis steps.
Conclusions:
- The findings confirm the presence of a thiolation center and the attachment of a 4'-phosphopantetheine cofactor, supporting the 'Multiple Carrier Model' of nonribosomal peptide biosynthesis.
- The study enhances the understanding of the functional significance of conserved residues within NPS modules.
- The research contributes to a broader discussion on the modular architecture and operational mechanisms of peptide synthetases.