PRESENCE AND CELLULAR-DISTRIBUTION OF A 60-KDA PROTEIN RELATED TO MITOCHONDRIAL HSP60 IN GIARDIA-LAMBLIA

Giardia lamblia trophozoites contain a 60-kDa protein recognized in im munoblots by antibody to mammalian hsp60, a protein localized in mitoc hondria in eukaryotic cells. The cellular distribution of this protein is evaluated by immunofluorescence microscopy using monoclonal antibo dy to human hsp60, polyclonal antibody to rodent hsp60, and 2 monoclon al antibodies to mycobacterial 65-kDa antigen, a prokaryotic hsp60 hom olog. W of these antibodies, except 1, which is specific for prokaryot ic hsp60, give a punctate labeling pattern throughout the cytoplasm, i ndicating that the 60-kDa protein is concentrated at discrete sites in the cytoplasm. The polyclonal hsp60 antiserum reveals additional punc tate labeling colocalized on axonemes of the anterior flagella. Postem bedment immunogold labeling and electron microscopy confirm that the a ntigen is clustered at foci in the cytoplasm but show no evidence of a ssociation with a membranous organelle. The hsp60 reactivity is also o bserved on anterior axonemes within the cytoplasm and on the adhesive disc. Hoechst 33258 DNA staining as well as electron microscopy give n o evidence of endosymbionts, so a false positive due to a prokaryotic hsp60 homolog is unlikely. The presence of an hsp60-related protein in G. lamblia raises interesting questions concerning its origin.