title: Characterization of a differentially expressed protein that shows an unusual localization to intracellular membranes in Leishmania major.
abstract: The SHERP genes are found as a tandem pair within the differentially regulated LmcDNA16 locus of Leishmania major. The SHERP gene product (small hydrophilic endoplasmic reticulum-associated protein) is unusual in its small size (6.2 kDa), its acidic pI (4.6) and its exclusive, high-level expression ( approximately 100000 copies per cell) in infective non-replicative parasite stages. No homologues have been found to date. Secondary-structure predictions suggest that SHERP contains an amphiphilic alpha-helix that is presumably involved in protein-protein interactions. SHERP has been localized to the endoplasmic reticulum as well as to the outer mitochondrial membrane in both wild-type and over-expressing parasites. Given the absence of an N-terminal signal sequence, transmembrane-spanning domains or detectable post-translational modifications, it is likely that this hydrophilic molecule is a peripheral membrane protein on the cytosolic face of intracellular membranes. This weak membrane association has been confirmed in cell-fractionation assays, in which SHERP redistributes from the cytoplasmic to the membrane fraction after in vivo cross-linking. SHERP does not appear to be involved in rearrangements of the cytoskeleton or conservation of organelle morphology during parasite differentiation. The role of this novel protein, presumed to be part of a protein complex, in infective parasites that are nutrient-deficient and pre-adapted for intracellular survival in the mammalian host is under investigation.
authors.affiliation: Wellcome Trust Laboratories for Molecular Parasitology, Department of Biochemistry, Imperial College of Science, Technology and Medicine, London SW7 2AZ, UK.
authors.forename: E
authors.initials: E
authors.lastname: Knuepfer
authors.forename: Y D
authors.initials: YD
authors.lastname: Stierhof
authors.forename: P G
authors.initials: PG
authors.lastname: McKean
authors.forename: D F
authors.initials: DF
authors.lastname: Smith
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D017124:Conserved Sequence; D017931:DNA Primers / Q000235:genetics; D015870:Gene Expression; D017125:Genes, Protozoan; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D007526:Isoelectric Point; D018320:Leishmania major / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D008970:Molecular Weight; D017433:Protein Structure, Secondary; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D015800:Protozoan Proteins