Interactions of hypocrellin B with hyaluronan and photo-induced interactions

In the current work, the molecular recognition and interaction were studied by taking advantages of the environmentally sensitive fluorescence of hypocrellin B (HB) and the structural knowledge of hyaluronan (HYA), a polysaccharide over-expressed in tumor cells or tissues. Interestingly, it was found that, binding to HYA, the absorbance of HB would be greatly strengthened, suggesting HB fitting to a hydrophobic environment in HYA, while the fluorescence seriously quenched at pH 7.0, which was very distinct from the binding of HB to proteins, liposome, other polysaccharide molecules or HYA at pH 2.0. Synchronously, the particle size of HYA would become bigger after interaction with HB, suggesting an aggregation of HYA. Considering the spectral responses of HB and the particle size change of HYA, a specific interaction of HB with HYA was proposed, that is, an HB molecule would link two HYA molecules not only by hydrophobic interaction but also by formations of intermolecular hydrogen bonds at physiological pH values. Furthermore, the estimated binding constant suggests a quite high affinity of HB to HYA. Besides, an oxygen-dependent degradation of HYA and photobleaching of HB were observed via photosensitization of HB.