A PCR technique employing relatively conserved regions of variant- specific surface antigen(VSP) genes was developed to differentiate Giardia isolates. The regions of the VSPH7 protein responsible for Zn and mental binding was determined by the use of fusion peptides containing various regions of VSPH7. Although the previously defined LIM- RING finger-like region bound Zn, other regions also could bind metals, and this was most likely due to CXXCXnCXXXC motifs scattered throughout the protein. There is conservation of spacing between CXXC motifs in a subset of VSPs. These findings indicate a conservation of structure, but diversity in antigenicity. Prior studies identified a transcript (GLORF- C4) specific for Group 3 Giardia; however, antibodies produced to the fusion protein identified a similar protein in other groups. Therefore, homologous proteins are present in other Giardia groups, and the reason the transcripts are not identified is because the sequences differ. Other proteins have also be identified which differ among Giardia lamblia isolates.
