Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Schistosomiasis is one of the most prevalent human diseases and is caused by the long-term survival of parasitic blood flukes. Membrane constituents at the surface of these parasites play a major role in parasite metabolism and elaborate sophisticated mechanisms for evasion of the host immune response. Despite this fact, little is known about the molecular properties or functions of individual membrane proteins. This study provides information regarding two polypeptides associated with the apical plasma membrane (APM) of Schistosoma mansoni.;An in vitro system for studying protein phosphorylation in the isolated APM was developed and the protein substrates of endogenous protein kinase activity were described. A 24 kilodalton (kDa) phosphoprotein was characterized in detail. Analysis of the structure of this polypeptide by lectin affinity chromatography, endoglycosidase digestion and phase separation in Triton X-114 demonstrated that the 24 kDa molecule was an integral membrane protein with N-linked oligosaccharides. In addition, the 24 kDa phosphoprotein was shown to be a major APM immunogen by immunoprecipitation with anti-APM antisera and with antibodies affinity purified from the 24 kDa region of preparative Western blots.;In order to isolate cDNA clones encoding APM polypeptides, comprehensive cDNA expression libraries were constructed in {dollar}\lambda{dollar} bacteriophage vectors and were screened with anti-APM antisera. Two cDNA clones were isolated and their nucleotide sequences determined. One cDNA was 141 base pairs in length and was shown to encode antigenic determinants shared with the 24 kDa phosphoprotein antigen. This cDNA was not full length since the homologous mRNA was approximately 800 residues in length. A possible open reading frame from this cDNA however, contained a signal for N-linked glycosylation. A second near full-length cDNA of 2621 base pairs was also cloned and sequenced. An open reading frame deduced from this cDNA predicted a protein of 702 amino acids with a molecular weight of 76 kDa. The deduced protein sequence was shown to be similar to the known sequences of vertebrate calpains.;This study provides the basis for a detailed structure/function analysis of the membrane-associated polypeptides encoded by the cloned cDNAs.



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