A superior drug carrier – aponeocarzinostatin in partially unfolded state fully protects the labile antitumor enediyne

<p>Abstract</p> <p>Background</p> <p>Neocarzinostatin is a potent antitumor drug consisting of an enediyne chromophore and a protein carrier.</p> <p>Methods</p> <p>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.</p> <p>Results</p> <p>The partially unfolded protein is in molten globule-like state, in which ~60% and ~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.</p> <p>Conclusion</p> <p>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.</p