Studies on surface membrane proteins of Schistosoma mansoni

The protein composition of schistosome fractions extracted from adult worms of S. mansoni was studied by electrophoresis in thin-layer polyacrylamide gel in the presence of sodium dodecyl sulfate (SDS-gels). The SDS pattern showed a complex mixture of protein components with molecular weight range of approximately 28,000-112,000. Isoelectric focusing in thin-layer polyacrylamide gel (IEF) of radiolabelled fractions from adult worms was carried out. Patterns of the radiolabelled membrane fractions (membrane pellet and frozen- thawed supernatant) showed the presence of protein bands at pH between 7.2-8.2. These bands were absent in fractions prepared from the whole worm without membrane. The stained IEF gels of the same fractions had confirmed the results obtained with the radiolabelled fractions. It was concluded that there is a specific component(s) in the membrane fractions with isoelectric points at pH between 7.2-8.2. This component(s) was termed the basic protein (BP) and found to be present in radiolabelled fractions extracted from the schistosomular stage of the parasite. BP appeared to be synthesized by the parasite as shown by internal radiolabelling of adult worms and schistosomula. However, it has been found that the basic region of the IEF gel (pH 7.2-8.2) does contain mouse immunoglobulins. But, on the specific removal of these immunoglobulins, the parasite antigens were still detectable by the coomassie blue staining. In addition, antibodies in rabbit antiserum raised specifically against partially purified BP showed no binding to the schistosomular surface membrane. Thus, BP might not be expressed on the outer surface of the parasite. The function of BP present in the surface membrane of the parasite is not clear. Yet, it might contribute to the integrity of the eleotronegatively charged schistosome tegument, by associating with the acidic phospholipids shown to be present in the tegument of adult worms. The frozen-thawed supernatant fraction (PTS) was used to study some characteristics of surface membrane proteins of adult schistosomes. It appeared to contain a complex mixture of proteins and glycoproteins. Antibodies in immune mouse serum collected at late stages of infection with S. mansoni recognized at least 3 antigens in the FTS fraction. Attempts to assess the amounts of radioactively labelled antigens recognized by mouse antibodies had met with limited success. This fraction contained some immunoglobulin classes and subclasses, mainly, IgG[2a], IgG[2b] and IgA, but not egg antigen. Isoelectric focusing of the FTS fractions extracted from individual clones of S. mansoni showed the presence of BP in all clones examined. But, BP was less labelled in some clones than in the others. It was concluded that BP is synthesized by all clones yet at different rates. Differences in the rate of incorporation of [35](S)-methionine into the surface membranes of schistosomula and adult worms derived from individual clones were reported. In addition, a direct correlation between the percentage of recovery of adult worms from mice infected with individual clones of S. mansoni and the rate of incorporation of [35](S)-methionine into schistosomula of these particular clones was noticed. It was suggested that the high rate of metabolism shown by an individual clone may account for the enhanced survival of the cercariae derived from that clone during penetration of the skin and migration through the vertebrate host