Discovery and characterization of novel cyclotides originated from chimeric precursors consisting of Albumin-1 chain a and cyclotide domains in the Fabaceae family
Nguyen, Giang Kien Truc
Nguyen, Ngan Thi Kim
Nguyen, Phuong Quoc Thuc
Chiu, Ming Sheau
Tam, James P.
Date of Issue2011
School of Biological Sciences
The tropical plant Clitoria ternatea is a member of the Fabaceae family well known for its medicinal values. Heat extraction of C. ternatea revealed that the bioactive fractions contained heat-stable cysteine-rich peptides (CRPs). The CRP family of A1b (Albumin-1 chain b/leginsulins), which is a linear cystine knot CRP, has been shown to present abundantly in the Fabaceae. In contrast, the cyclotide family, which also belongs to the cystine knot CRPs but with a cyclic structure, is commonly found in the Rubiaceae, Violaceae, and Cucurbitaceae families. In this study, we report the discovery of a panel of 15 heat-stable CRPs, of which 12 sequences (cliotide T1-T12) are novel. We show unambiguously that the cliotides are cyclotides and not A1bs, as determined by their sequence homology, disulfide connectivity, and membrane active properties indicated by their antimicrobial activities against Escherichia coli and cytotoxicities to HeLa cells. We also show that cliotides are prevalent in C. ternatea and are found in every plant tissue examined, including flowers, seeds, and nodules. In addition, we demonstrate that their precursors are chimeras, half from cyclotide and the other half from Albumin-1, with the cyclotide domain displacing the A1b domain in the precursor. Their chimeric structures likely originate from either horizontal gene transfer or convergent evolution in plant nuclear genomes, which are exceedingly rare events. Such atypical genetic arrangement also implies a different mechanism of biosynthetic processing of cyclotides in the Fabaceae and provides new understanding of their evolution in plants.
The journal of biological chemistry
© 2011 The American Society for Biochemistry and Molecular Biology. This is the author created version of a work that has been peer reviewed and accepted for publication by Discovery and Characterization of Novel Cyclotides Originated from Chimeric Precursors Consisting of Albumin-1 Chain a and Cyclotide Domains in the Fabaceae Family, JBC Papers in Press. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: http://dx.doi.org/10.1074/jbc.M111.229922.