title: A superior drug carrier--aponeocarzinostatin in partially unfolded state fully protects the labile antitumor enediyne.
abstract: BACKGROUND
  Neocarzinostatin is a potent antitumor drug consisting of an enediyne chromophore and a protein carrier.
  
  
  METHODS
  We characterized an intermediate in the equilibrium unfolding pathway of aponeocarzinostatin, using a variety of biophysical techniques including 1-anilino-8-napthalene sulfonate binding studies, size-exclusion fast protein liquid chromatography, intrinsic tryptophan fluorescence, circular dichroism, and 1H-15N heteronuclear single quantum coherence spectroscopy.
  
  
  RESULTS
  The partially unfolded protein is in molten globule-like state, in which approximately 60% and approximately 20% tertiary and secondary structure is disrupted respectively. Despite lacking a fully coordinated tertiary structure for assembling a functional binding cleft, the protein in molten globule-like state is still able to fully protect the labile chromophore. Titration of chromophore leads the partially denatured apoprotein to fold into its native state.
  
  
  CONCLUSIONS
  These findings bring insight into conserving mechanism of neocarzinostatin under harsh environment, where even the partially denatured apoprotein exhibits protective effect, confirming the superiority of the drug carrier.
authors.affiliation: Department of Chemistry, National Chung Hsing University, Taichung, Taiwan, Republic of China. cyu.nthu@gmail.com
authors.forename: Aranganathan
authors.initials: A
authors.lastname: Shanmuganathan
authors.forename: Thallapuranam Krishnaswamy Suresh
authors.initials: TK
authors.lastname: Kumar
authors.forename: Chiy-Mey
authors.initials: CM
authors.lastname: Huang
authors.forename: Chin
authors.initials: C
authors.lastname: Yu
authors.forename: Der-Hang
authors.initials: DH
authors.lastname: Chin
mesh_terms: D000970:Antineoplastic Agents / Q000008:administration & dosage* / Q000737:chemistry; D001059:Apoproteins / Q000737:chemistry*; D001665:Binding Sites; D002942:Circular Dichroism; D004337:Drug Carriers / Q000737:chemistry*; D053281:Enediynes / Q000008:administration & dosage* / Q000737:chemistry; D019791:Guanidine / Q000494:pharmacology; D008958:Models, Molecular; D011487:Protein Conformation; D017510:Protein Folding; D009353:Zinostatin / Q000737:chemistry*
chemical_list: D000970:Antineoplastic Agents; D001059:Apoproteins; D004337:Drug Carriers; D053281:Enediynes; C052401:aponeocarzinostatin; D009353:Zinostatin; D019791:Guanidine