Resolving the zinc binding capacity of honey bee vitellogenin and locating its putative binding sites

The protein vitellogenin (Vg) plays a central role in lipid transportation in most egg‐laying animals. High Vg levels correlate with stress resistance and lifespan potential in honey bees (Apis mellifera). Vg is the primary circulating zinc‐carrying protein in honey bees. Zinc is an essential metal ion in numerous biological processes, including the function and structure of many proteins. Measurements of Zn(2+) suggest a variable number of ions per Vg molecule in different animal species, but the molecular implications of zinc‐binding by this protein are not well‐understood. We used inductively coupled plasma mass spectrometry to determine that, on average, each honey bee Vg molecule binds 3 Zn(2+)‐ions. Our full‐length protein structure and sequence analysis revealed seven potential zinc‐binding sites. These are located in the β‐barrel and α‐helical subdomains of the N‐terminal domain, the lipid binding site, and the cysteine‐rich C‐terminal region of unknown function. Interestingly, two potential zinc‐binding sites in the β‐barrel can support a proposed role for this structure in DNA‐binding. Overall, our findings suggest that honey bee Vg bind zinc at several functional regions, indicating that Zn(2+)‐ions are important for many of the activities of this protein. In addition to being potentially relevant for other egg‐laying species, these insights provide a platform for studies of metal ions in bee health, which is of global interest due to recent declines in pollinator numbers.