A New Scaffold of an Old Protein Fold Ensures Binding to the Bisintercalator Thiocoraline

Tapan Biswas, Olga E. Zolova, Felipe Lombó, Fernando de la Calle, Jose A. Salas, Oleg V. Tsodikov, Sylvie Garneau-Tsodikova

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


Thiocoraline is a thiodepsipeptide with potent antitumor activity. TioX, a protein with an unidentified function, is encoded by a gene of the thiocoraline biosynthetic gene cluster. The crystal structure of the full-length TioX protein at 2.15 Å resolution reveals that TioX protomer shares an ancient βαβββ fold motif with glyoxalase I and bleomycin resistance protein families, despite a very low sequence homology. Intriguingly, four TioX monomers form a unique 2-fold symmetric tetrameric assembly that is stabilized by four intermolecular disulfide bonds formed cyclically between Cys60 and Cys66 of adjacent monomers. The arrangement of two of the four monomers in the TioX tetramer is analogous to that in dimeric bleomycin resistance proteins. This analogy indicates that this novel higher-order structural scaffold of TioX may have evolved to bind thiocoraline. Our equilibrium titration studies demonstrate the binding of a thiocoraline chromophore analog, quinaldic acid, to TioX, thereby substantiating this model. Furthermore, a strain of Streptomyces albus containing an exogenous thiocoraline gene cluster devoid of functional tioX maintains thiocoraline production, albeit with a lower yield. Taken together, these observations rule out a direct enzymatic function of TioX and suggest that TioX is involved in thiocoraline resistance or secretion.

Original languageEnglish
Pages (from-to)495-507
Number of pages13
JournalJournal of Molecular Biology
Issue number2
StatePublished - Mar 26 2010

Bibliographical note

Funding Information:
This work was supported by start-up funds from the Life Sciences Institute (to S.G.-T.) and the College of Pharmacy (to S.G.-T. and O.V.T.) at the University of Michigan and by the Vahlteich Research Award Fund, College of Pharmacy at the University of Michigan (to S.G.-T.). Research performed at JAS laboratory was funded by Red Temática de Investigación Cooperativa de Centros de Cáncer (ISCIII-RETIC RD06/0020/0026; Ministry of Health, Spain). We thank Jessica M. Pero for the cloning of the His-tagged wild-type TioX and for the preparation of its SeMet-substituted variant. We thank Dr. Spencer Anderson and the staff of sectors LS-CAT and GM/CA-CAT at the Advanced Photon Source at the Argonne National Laboratory for assistance with the X-ray diffraction data collection.


  • bacterial resistance
  • bisintercalator
  • hydrophobic pocket
  • thiocoraline
  • tryptophan fluorescence

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology


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