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Biosynthesis of circular proteins in plants
Amanda D Gillon1, Ivana Saska, Cameron V Jennings
1Department of Biochemistry, La Trobe University, Melbourne, Victoria 3086, Australia.
The Plant Journal : for Cell and Molecular Biology
|December 19, 2007
Summary
Researchers investigated how plant cyclotides are made. They found specific mutations prevent circularization, suggesting two distinct processing pathways exist in plants for producing mature cyclotides.
Area of Science:
- Biochemistry
- Plant Science
- Molecular Biology
Background:
- Plant cyclotides are circular proteins derived from linear precursors.
- The precise mechanism for cyclotide domain excision and N-/C-terminus ligation remains unclear.
Purpose of the Study:
- To elucidate the production mechanism of the prototypic cyclotide kalata B1 from its precursor Oak1.
- To investigate the role of conserved residues and motifs in cyclotide processing.
Main Methods:
- Immunoprecipitation experiments were used to study protein interactions.
- MALDI-TOF mass spectrometry analyzed peptide products in different plant species.
Main Results:
- Oldenlandia affinis exclusively produced mature kalata B1.
- Transgenic plants (Arabidopsis thaliana, Nicotiana tabacum, N. benthamiana) produced both linear and circular forms.
- Mutations at the conserved C-terminal asparagine residue or truncation of the tripeptide motif abolished circular peptide production.
Conclusions:
- Two distinct in planta processing pathways are proposed: one yielding mature cyclotides and another producing non-cyclizable linear variants.
- Conserved C-terminal residues and motifs are critical for the cyclization step in plant cyclotide biosynthesis.
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