Trichinella spiralis secretes a homologue of prosaposin.
Infective larvae and adult stage Trichinella spiralis secrete a protein homologous to prosaposin, the precursor of sphingolipid activator proteins (saposins) A-D originally defined in vertebrates. The protein contains four saposin domains, with the six cysteine residues which form the three intramolecular disulphide bonds in close register in each case. It differs substantially from vertebrate prosaposins in the N-terminal prodomain, the region separating saposins A and B, and completely lacks the C-terminal domain which has been demonstrated to be essential for lysosomal targetting in these organisms. The protein is secreted in unprocessed form with an estimated mass of 56 kDa, and contains a single N-linked glycan which is bound by the monoclonal antibody NIM-M1, characteristic of the TSL-1 antigens which are capped by tyvelose (3,6-dideoxy-D-arabinohexose). Immuno-electron microscopy localised the protein to membrane-bound vesicles and more complex multi-lamellar organelles in diverse tissues including the hypodermis, intestine and stichosomes, although it was absent from the dense-core secretory granules typical of the latter. Possible functions of a secreted prosaposin are discussed.
Department of Biological Sciences, Biochemistry Building, Imperial College London, London SW7 2AZ, UK. m.selkirk@imperial.ac.uk
Murray E
ME
Selkirk
Ayman S
AS
Hussein
Anne E
AE
Chambers
David
D
Goulding
Marie-Pierre
MP
Gares
Celia
C
Vásquez-Lopez
Teresa
T
Gárate
R Michael E
RM
Parkhouse
Kleoniki
K
Gounaris
D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry; D017124:Conserved Sequence; D003545:Cysteine / Q000737:chemistry / Q000235:genetics; D018509:DNA, Helminth / Q000737:chemistry / Q000302:isolation & purification; D015801:Helminth Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006601:Hexoses / Q000737:chemistry; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D008970:Molecular Weight; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D049231:Saposins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D017160:Trichinella spiralis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
D018509:DNA, Helminth; D015801:Helminth Proteins; D006601:Hexoses; D049231:Saposins; C009616:tyvelose; D003545:Cysteine