Metal-dependent hydrolysis of myelin basic protein by IgGs from the sera of patients with multiple sclerosis

Homogeneous IgG fractions were obtained by chromatography of the sera of patients with multiple sclerosis (MS) on Protein G-Sepharose under conditions that remove non-specifically bound proteins. These IgGs contained several chelated metals, the relative amount of which decreases in the order: Fe ≥ Ca > Cu ≥ Zn ≥ Mg ≥ Mn ≥ Pb ≥ Co ≥ Ni. In contrast to homogeneous IgGs of healthy individuals, Abs of MS patients effectively hydrolyzed human myelin basic protein (MBP). A minor metal-dependent fraction was obtained by chromatography of highly purified IgGs from MS patient on Chelex-100. This IgG fraction did not hydrolyze human MBP in the absence of Me2+ ions but was activated after addition of Me2+ ions: Mg2+ > Mn2+ > Cu2+ > Ca2+. Proteolytic activities of IgGs from other MS patients were also activated by other metal ions (Ni2+, Fe2+, Co2+, Zn2+, Pb2+, and Co2+) and especially Ni2+. Ni2+-activated IgGs were separated into distinct MBP-hydrolyzing fractions by chromatography on HiTrap™ Chelating Sepharose charged with Ni2+. Detection of Mg2+-dependent proteolytic activity in the SDS-PAGE area corresponding only to IgG provided direct evidence that IgG from sera of MS patients possesses metal-dependent human MBP-hydrolyzing activity. Observed properties of MS abzymes distinguish them from other known mammalian metalloproteases and demonstrate their pronounced catalytic diversity. Metal-dependent IgGs from MS patients represent the first example of abzymes with metal-dependent proteolytic activity.