Interaction of glucose with hemoglobin: a study in aqueous solution and at the air-water interface using the Langmuir-Blodgett technique

Here, we report the glycosylation of human adult hemoglobin (Hb) studied in aqueous solution and at the air-water interface by the Langmuir-Blodgett (LB) technique. Pressure-area (pi-A) and pressure-time (pi-t) measurements show that the concentration of glucose (GLC) and interaction time have an effect on Hb molecular area as well as on surface activity. Solution studies by UV-vis absorption and emission spectroscopy show that the GLC can alter the local conformation of Hb to some extent at the tryptophan and heme residues. CD spectroscopic studies in solution indicate that the alpha-helix content increases in the presence of GLC at the secondary structure level, which may be the cause of an increased adsorption rate of Hb. Also, secondary structure calculation using FTIR technique in the LB film follows the decrease in alpha-helix and increase in beta-sheet structure as well as the formation of intermolecular aggregates. AFM images of Hb in the LB film indicate the transition from globular to an ellipsoid-like structure of Hb in the presence of GLC. FTIR studies of the LB film support the AFM imaging and the analysis of pi-t kinetics. The molecular docking study revealed that Val 1 and Lys 132 are the most favorable docked sites along with some other sites such as Hem 147, Trp 37, Asp 94, Tyr 145, Leu 91, His 143, Glu 43 etc. The overall study may predict the processes of interactions with the increased concentration of GLC on Hb as well as on other long lived proteins.