Anti Zn antibodies: Cross reactivity and competitive binding with heavy metals

Monoclonal antibodies of IgM class, specific to IDA-Zn were used for evaluating their Zn2+ binding efficiency in the presence of trace metal ions such as Cr3+ Cr6+, Cu2+ and Cd2+. In the present work, antibody raised against the hapten IDA-Zn(II) was pre-incubated with different metal ions and the binding capacity to the specific hapten was tested using ELISA and immobilized metal ion affinity chromatography (IMAC) techniques. IMAC was carried out with the free antibody and antibody pre-incubated with selected heavy metal ions using Sepharose IDA-Zn2+ column and the same samples were tested using a hapten specific ELISA with non-protein hapten carrier. Different effects were observed after pre-incubation with metal ions. Cr3+ exhibited synergistic binding where as antagonism was detected with Cd2+. The synergistic effect observed with Cr3+ suggests involvement of binding sites other than that of zinc and conformational changes that result from Cr3+ binding. It is probable that, this binding event also increases the accessibility of the zinc binding sites on IgM. On the same lines, the antagonism observed with Cd2+ could be attributed to structural changes resulting in reduced accessibility to zinc binding sites. In case of Cr6+, no appreciable change in binding to IDA-Zn was observed while Cu2+ showed competitive binding.