Identification of phosphatidylcholine transfer protein-like in the parasite Entamoeba histolytica

Caveolin is the protein marker of caveola-mediated endocytosis. Previously, we demonstrated by immunoblotting and immunofluorescence that an anti-chick embryo caveolin-1 monoclonal antibody (mAb) recognizes a protein in amoeba extracts. Nevertheless, the caveolin-1 gene is absent in the Entamoeba histolytica genome database. In this work, the goal was to isolate, identify and characterize the protein that cross-reacts with chick embryo caveolin-1. We identified the protein using a proteomic approach, and the complete gene was cloned and sequenced. The identified protein, E. histolytica phosphatidylcholine transfer protein-like (EhPCTP-L), is a member of the StAR-related lipid transfer (START) protein superfamily. The human homolog binds and transfers phosphatidylcholine (PC) and phosphatidylethanolamine (PE) between model membranes in vitro; however, the physiological role of PCTP-L remains elusive. Studies in silico showed that EhPCTP-L has a central START domain and also contains a C-terminal intrinsically disordered region. The anti-rEhPCTP-L antibody demonstrated that EhPCTP-L is found in the plasma membrane and cytosol, which is in agreement with previous reports on the human counterpart. This result points to the plasma membrane as one possible target membrane for EhPCTP-L. Furthermore, assays using filipin and nystatin showed down regulation of EhPCTP-L, in an apparently cholesterol-independent way. Interestingly, EhPCTP-L binds primarily to anionic phospholipids phosphatidylserine (PS) and phosphatidic acid (PA), while its mammalian counterpart HsPCTP-L binds neutral phospholipids PC and PE. The present study provides information that helps reveal the possible function and regulation of PCTP-L expression in the primitive eukaryotic parasite E. histolytica.