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Chem Biol. 2015 May 21;22(5):571-82. doi: 10.1016/j.chembiol.2015.04.010. Epub 2015 May 7.

Peptide macrocyclization by a bifunctional endoprotease.

Author information

1
The University of Western Australia, School of Chemistry and Biochemistry, 35 Stirling Highway, Crawley, Perth 6009, Australia; ARC Centre of Excellence in Plant Energy Biology, 35 Stirling Highway, Crawley, Perth 6009, Australia.
2
ARC Centre of Excellence in Plant Energy Biology, 35 Stirling Highway, Crawley, Perth 6009, Australia.
3
The University of Queensland, Institute for Molecular Bioscience, Brisbane 4072, Australia.
4
The University of Western Australia, School of Chemistry and Biochemistry, 35 Stirling Highway, Crawley, Perth 6009, Australia; ARC Centre of Excellence in Plant Energy Biology, 35 Stirling Highway, Crawley, Perth 6009, Australia. Electronic address: joshua.mylne@uwa.edu.au.

Abstract

Proteases usually cleave peptides, but under some conditions, they can ligate them. Seeds of the common sunflower contain the 14-residue, backbone-macrocyclic peptide sunflower trypsin inhibitor 1 (SFTI-1) whose maturation from its precursor has a genetic requirement for asparaginyl endopeptidase (AEP). To provide more direct evidence, we developed an in situ assay and used (18)O-water to demonstrate that SFTI-1 is excised and simultaneously macrocyclized from its linear precursor. The reaction is inefficient in situ, but a newfound breakdown pathway can mask this inefficiency by reducing the internal disulfide bridge of any acyclic-SFTI to thiols before degrading it. To confirm AEP can directly perform the excision/ligation, we produced several recombinant plant AEPs in E. coli, and one from jack bean could catalyze both a typical cleavage reaction and cleavage-dependent, intramolecular transpeptidation to create SFTI-1. We propose that the evolution of ligating endoproteases enables plants like sunflower and jack bean to stabilize bioactive peptides.

PMID:
25960260
DOI:
10.1016/j.chembiol.2015.04.010
[Indexed for MEDLINE]
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