Molecular recognition patterns between vitamin B12 and human serum albumin explored through STD–NMR and spectroscopic methods

Ligand-receptor molecular recognitionis the basis of biological process. The Saturation Transfer Difference-NMR (STD-NMR) technique has been recently used to gain qualitative and quantitative information about physiological interactions at atomic-resolution. The molecular recognition patterns between Vitamin B12 (VB12) and human serum albumin (HSA) were investigated by STD-NMR supplemented by other spectroscopies and molecular docking. STD-NMR delivered a complete picture that the substituent groups on the tetrapyrrole ring of VB12 interacted with site III of HSA through binding epitope mapping and competitive probe experiments. STD-NMR and fluorescence results proved the moderate binding capability of VB12 and clarified a static, spontaneous, and temperature-sensitive binding mechanism. 3D-fluorencence, FT-IR and circular dichroism spectra showed a compact protein structure by interacting with VB12. Size distribution and surface hydrophobicity showed the surface properties changes of HSA caused by the binding of VB12. Computer simulation confirmed the recognition mode in theory and was compared with experiments. This work is beneficial for understanding the safety and biological action of VB12, and will attract researchers interested in NMR technology.