Schistosomiasis is a parasitic disease initiated by the deposition of
eggs in host tissues by the blood fluke Schistosoma. A gene encoding a
low-molecular weight GTP-binding protein (LMWGP) was cloned from Schi
stosoma mansoni using a polymerase chain reaction (PCR)-based strategy
. The gene was termed smrab (Schistosoma mansoni rab-related protein).
Northern blot analysis hybridizes smrab cDNA with a 1.5-kb band of mR
NA; this mRNA is abundantly expressed in male schistosomes, while only
slightly in females. The deduced amino acid sequence of smrab shares
ca. 70% homology with that of several rab-related LMWGPs. Smrab termin
ates in a CCXXX motif, which is one of several signals for post-transl
ational isoprenoid modification by geranylgeranyl protein transferase
(GGPT) type II. A GGPT assay with in vitro translation product confirm
s that smrab is geranylgeranylated. Recombinant expression of smrab in
the pET3a expression vector yields insoluble protein which migrates a
s a 23-kDa band on SDS-PAGE. N-terminal sequence information of the re
combinant protein matches the predicted amino acid sequence of smrab.
GTP-binding analysis indicates that the recombinant protein binds GTP.
Therefore, smrab meets the criteria recently established for acceptan
ce into the ras superfamily of GTP-binding proteins (Kahn, R.A., Der,
C.J. and Bokoch, G.M. (1992) The ras superfamily of GTP-binding protei
ns: guidelines on nomenclature. FASEB J. 6, 2512-2513, Ref. [21]).