Stage-specific expression of a Schistosoma mansoni polypeptide similar to the vertebrate regulatory protein stathmin

The ubiquitous vertebrate protein stathmin is expressed and phosphorylated in response to a variety of external and internal signals. Stathmin, in tur n, controls cell growth and differentiation through its capacity to regulat e microtubule assembly dynamics. This is the first report on the molecular cloning and characterization of a stathmin-like protein (SmSLP) in an inver tebrate, the human blood fluke Schistosoma mansoni. SmSLP is first synthesi zed at high levels in the intermediate molluscan host and completely disapp ears 48 h after penetration into the mammalian host. The protein is prefere ntially iodinated in intact immature parasites using the Bolton-Hunter reag ent, can be quantitatively extracted in high salt buffers, and remains solu ble after boiling. Native SmSLP was partially sequenced, and its complete s tructure was derived from the cloning and sequencing of its cDNA, The seque nce is up to 26% identical to vertebrate stathmin sequences and contains tw o potential phosphorylation sites. Native SmSLP is indeed phosphorylated be cause phosphatase digestion shifts its mobility in electrofocusing gels. Sm SLP associates with tubulin, as suggested by immune co-precipitation result s. Irt vitro experiments demonstrated that SmSLP inhibits tubulin assembly and causes the depolymerization of preassembled microtubules, thus probably fulfilling regulatory roles in critical steps of schistosome development.