Physical, structural, and functional properties of the β1 integrin-like fibronectin receptor (β1EhFNR) in Entamoeba histolytica

The presence in Entamoeba histolytica of a fibronectin (FN) receptor, which is antigenically related to β1 integrin-like molecules and shows 99% homology with the intermediate subunit-2 of the Gal/GalNAc-specific lectin has been described. The E. histolytica genome has been sequenced, and its analysis shows no integrin sequences. Here we provide further evidence to demonstrate that this molecule behaves as integrin-like in its physical, structural and functional properties. The purified β1EhFNR complex is resolved into three polypeptides of 150, 140, and 130 kDa. Transmission electron microscopy showed individual complexes consisting of oblong heads of 3 nm × 4 nm and two projecting arms 6–7 nm in length. In the absence of detergent, these complexes formed aggregates that were composed of clusters or “rosettes” of between two and six or more β1EhFNR complexes. The physical properties of the purified β1EhFNR complexes were: RS = 5.8 nm, S20W = 8.3, f/f0 = 1.4. This complex was seen in close physical association with adhesion plates and phagocytic invaginations, using confocal microscopy and the 3C10 mAb that recognizes these three subunits complex. Regulation of its surface expression is not dependent on protein synthesis; rather it is regulated by inward and outward mobilization of the molecules. The presence and antigenic similarity of putative β1EhFNRs in different strains and species of Entamoeba was analyzed using the 3C10 mAb; this mAb recognized the complex in all E. histolytica species, however there was no recognition in E. dispar, E. invadens, and Laredo strains. Finally, evidence is provided about post-translational modifications such as tyrosine phosphorylation and glycosylation suffered by the β1EhFNR complex.