Circular Proteins in Plants

Much interest has been generated by recent reports on the discovery of circular (i.e. head-to-tail cyclized) proteins in plants. Here we report the three-dimensional structure of one of the newest such circular proteins, MCoTI-II, a novel trypsin inhibitor fromMomordica cochinchinensis, a member of the Cucurbitaceae plant family. The structure consists of a small β-sheet, several turns, and a cystine knot arrangement of the three disulfide bonds. Interestingly, the molecular topology is similar to that of the plant cyclotides (Craik, D. J., Daly, N. L., Bond, T., and Waine, C. (1999) J. Mol. Biol. 294, 1327–1336), which derive from the Rubiaceae and Violaceae plant families, have antimicrobial activities, and exemplify the cyclic cystine knot structural motif as part of their circular backbone. The sequence, biological activity, and plant family of MCoTI-II are all different from known cyclotides. However, given the structural similarity, cyclic backbone, and plant origin of MCoTI-II, we propose that MCoTI-II can be classified as a new member of the cyclotide class of proteins. The expansion of the cyclotides to include trypsin inhibitory activity and a new plant family highlights the importance and functional variability of circular proteins and the fact that they are more common than has previously been believed. Insights into the possible roles of backbone cyclization have been gained by a comparison of the structure of MCoTI-II with the homologous acyclic trypsin inhibitors CMTI-I and EETI-II from the Cucurbitaceae plant family.

[1]  D. Craik,et al.  Chemical synthesis and folding pathways of large cyclic polypeptides: studies of the cystine knot polypeptide kalata B1. , 1999, Biochemistry.

[2]  H. Paulus,et al.  Protein splicing and related forms of protein autoprocessing. , 2000, Annual review of biochemistry.

[3]  L. Chiche,et al.  1H 2D NMR and distance geometry study of the folding of Ecballium elaterium trypsin inhibitor, a member of the squash inhibitors family. , 1989, Biochemistry.

[4]  K. Wüthrich.  NMR of proteins and nucleic acids , 1988 .

[5]  J. Thornton,et al.  AQUA and PROCHECK-NMR: Programs for checking the quality of protein structures solved by NMR , 1996, Journal of biomolecular NMR.

[6]  J Otlewski,et al.  The refined 2.0 Å X‐ray crystal structure of the complex formed between bovine β‐trypsin and CMTI‐I, a trypsin inhibitor from squash seeds (Cucurbita maxima) Topological similarity of the squash seed inhibitors with the carboxypeptidase A inhibitor from potatoes , 1989, FEBS letters.

[7]  J. Priestle,et al.  Structure of the complex of leech-derived tryptase inhibitor (LDTI) with trypsin and modeling of the LDTI-tryptase system. , 1997, Structure.

[8]  M Karplus,et al.  Application of molecular dynamics with interproton distance restraints to three-dimensional protein structure determination. A model study of crambin. , 1986, Journal of molecular biology.

[9]  Andreas Plückthun,et al.  Circular β‐lactamase: stability enhancement by cyclizing the backbone , 1999 .

[10]  A. Brünger,et al.  Torsion angle dynamics: Reduced variable conformational sampling enhances crystallographic structure refinement , 1994, Proteins.

[11]  L. Bohlin,et al.  Seven novel macrocyclic polypeptides from Viola arvensis. , 1999, Journal of natural products.

[12]  F Sandberg,et al.  Oldenlandia affinis (R&S) DC. A plant containing uteroactive peptides used in African traditional medicine. , 2000, Journal of ethnopharmacology.

[13]  David J. Craik,et al.  Acyclic Permutants of Naturally Occurring Cyclic Proteins , 2000, The Journal of Biological Chemistry.

[14]  L. Chiche,et al.  Squash trypsin inhibitors from Momordica cochinchinensis exhibit an atypical macrocyclic structure. , 2000, Biochemistry.

[15]  Q Huang,et al.  Refined 1.6 A resolution crystal structure of the complex formed between porcine beta-trypsin and MCTI-A, a trypsin inhibitor of the squash family. Detailed comparison with bovine beta-trypsin and its complex. , 1993, Journal of molecular biology.

[16]  S Luckett,et al.  High-resolution structure of a potent, cyclic proteinase inhibitor from sunflower seeds. , 1999, Journal of molecular biology.

[17]  K. Wüthrich,et al.  Torsion angle dynamics for NMR structure calculation with the new program DYANA. , 1997, Journal of molecular biology.

[18]  J Otlewski,et al.  Determination of the complete three-dimensional structure of the trypsin inhibitor from squash seeds in aqueous solution by nuclear magnetic resonance and a combination of distance geometry and dynamical simulated annealing. , 1989, Journal of molecular biology.

[19]  A T Brünger,et al.  Torsion-angle molecular dynamics as a new efficient tool for NMR structure calculation. , 1997, Journal of magnetic resonance.

[20]  J. Tam,et al.  An unusual structural motif of antimicrobial peptides containing end-to-end macrocycle and cystine-knot disulfides. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[21]  K. Gustafson,et al.  Solution structure by NMR of circulin A: a macrocyclic knotted peptide having anti-HIV activity. , 1999, Journal of molecular biology.

[22]  J. Otlewski,et al.  High-resolution structures of three new trypsin-squash-inhibitor complexes: a detailed comparison with other trypsins and their complexes. , 1999, Acta crystallographica. Section D, Biological crystallography.

[23]  I. Campbell,et al.  Elucidation of the primary and three-dimensional structure of the uterotonic polypeptide kalata B1. , 1995, Biochemistry.

[24]  J. Thornton,et al.  PROMOTIF—A program to identify and analyze structural motifs in proteins , 1996, Protein science : a publication of the Protein Society.

[25]  T. C. Evans,et al.  The Cyclization and Polymerization of Bacterially Expressed Proteins Using Modified Self-splicing Inteins* , 1999, The Journal of Biological Chemistry.

[26]  P. Anderson,et al.  Cyclopsychotride A, a biologically active, 31-residue cyclic peptide isolated from Psychotria longipes. , 1994, Journal of natural products.

[27]  L. Pannell,et al.  New circulin macrocyclic polypeptides from Chassalia parvifolia. , 2000, Journal of natural products.

[28]  L. Pannell,et al.  Circulins A and B. Novel human immunodeficiency virus (HIV)-inhibitory macrocyclic peptides from the tropical tree Chassalia parvifolia. , 1994 .

[29]  C. Chi,et al.  Protein, cDNA, and genomic DNA sequences of the towel gourd trypsin inhibitor. A squash family inhibitor. , 1993, The Journal of biological chemistry.

[30]  W. Hendrickson,et al.  A structural superfamily of growth factors containing a cystine knot motif , 1993, Cell.

[31]  M. Karplus,et al.  CHARMM: A program for macromolecular energy, minimization, and dynamics calculations , 1983 .

[32]  D. Craik,et al.  A common structural motif incorporating a cystine knot and a triple‐stranded β‐sheet in toxic and inhibitory polypeptides , 1994, Protein science : a publication of the Protein Society.

[33]  M. Billeter,et al.  MOLMOL: a program for display and analysis of macromolecular structures. , 1996, Journal of molecular graphics.

[34]  K Wüthrich,et al.  Efficient analysis of protein 2D NMR spectra using the software packageEASY , 1991, Journal of biomolecular NMR.

[35]  S. Benkovic,et al.  Production of cyclic peptides and proteins in vivo. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[36]  D. Craik,et al.  The cystine knot motif in toxins and implications for drug design. , 2001, Toxicon : official journal of the International Society on Toxinology.

[37]  L. Pannell,et al.  Cycloviolins A-D, anti-HIV macrocyclic peptides from Leonia cymosa. , 2000, The Journal of organic chemistry.