Spectroscopic Properties of Non-glycosilated Functional Unit KLH2-c of Keyhole Limpet Hemocyanin

The functional unit KLH2-c, isolated from the structural subunit KLH2 of keyhole limpet Megathura crenulata hemocyanin, was studied to explain the effect of the oligosaccharide component for the conformational stability of the protein. The properties of this FU were characterized by fluorescence spectroscopy, combined with fluorescence quenching studies, using acrylamide, caesium chloride and potassium iodide as tryptophan quenchers. Using circular dichroism and fluorescence spectroscopy, the thermostability of the non-glycosylated FU KLH2-c was studied in comparison to the glycosylated native molecule, the structural subunits KLH1, KLH2 and the FU RvH1-a of Rapana venosa Hc. The melting Tm (45°C) as well as the critical temperatures Tc (46) were found to be less for KLH2-c compared to the glycosylated forms which could be explained to be caused by the presence of oligosaccharide side chains and aggregation effects.