Isolation and characterization of cDNA clones encoding a 32-kDa dense-granule antigen of Sarcocystis muris (Apicomplexa)

A monoclonal antibody (2F4) directed against a 32-kDa dense-granule antigen of Sarcocystis muris cyst merozoites (bradyzoites) was used to screen a lambda ZAP cDNA expression library. A clone with an insert of 1.4 kb in length (DG 32/1) was isolated. A fusion protein derived from bacteria harbouring the recombinant plasmid DG 32/1 reacted with monoclonal antibody (mAb) 2F4. Southern blot hybridization suggests that the gene is present as a single copy. On Northern blots, a single mRNA species of 1.8 kb was detected by a cDNA-derived probe. In addition, we isolated a full-length clone (DG 32/PH1) by screening the cDNA library with a non-radioactive-labelled cDNA probe. The nucleotide sequence of DG 32/PH1 comprises 1.57 kb. It contains an open reading frame of 882 bp with a coding capacity of approximately 32 kDa. The hypothetical polypeptide consists of a putative N-terminal signal peptide and the mature protein sequence. The occurrence of an N-terminal signal sequence is consistent with the observation that the 32-kDa protein of S. muris is secreted from the dense granules.

Characterization of a 14 kDa oocyst wall protein of Eimeria tenella and E. acervulina

We have extracted a protein of 14 kDa from purified oocyst walls of several Eimeria species. Polyclonal antibodies were raised in rats against the 14 kDa proteins of E. acervulina and E. tenella. On immunoblots these antisera reacted in a highly specific manner with the homologous 14 kDa antigens, but not with heterologous antigens. In addition, specific binding of the two antisera to oocyst wall fragments of E. acervulina and E. tenella was demonstrated by immunofluorescence. Partial amino-terminal sequences comprising 20 amino acid residues were obtained from the 14 kDa oocyst wall proteins of E. acervulina and E. tenella. They are characterized by an abundance of amino acids containing hydroxyl groups in their side chains (serine, tyrosine, threonine). Binding of the oocyst wall protein of E. tenella by peanut agglutinin indicates the presence of O-linked carbohydrates.

Characterization of cDNA clones encoding a major microneme antigen of Sarcocystis muris (Apicomplexa) cyst merozoites

Two monoclonal antibodies directed against a microneme antigen of Sarcocystis muris cyst merozoites (16/17 kDa band doublet) were used to isolate cDNA clones from a lambda ZAP expression library. Restriction analysis revealed that the inserts were highly similar, with sizes ranging between 1.8 and 2.3 kb. In addition, a full-length cDNA insert of 2.6 kb was obtained by hybridization screening. On Northern blots, a single mRNA species of 2.7 kb was detected by a cDNA-derived probe. Southern blot hybridization suggests that the gene is present as a single copy. The nucleotide sequence of the full-length clone contains a single reading frame with a coding capacity of 26.5 kDa. The hypothetical polypeptide consists of a putative N-terminal signal peptide followed by a hydrophilic domain of unknown function, and the mature protein sequence. After purifying the 16/17 kDa antigen from cyst merozoites, a partial N-terminal amino acid sequence was obtained. Thus, the identity of the cDNA sequence was confirmed. The deduced sequence of the mature protein is predominantly hydrophilic and rich in cysteine (8.7%). Database searching suggested weak homologies of the hypothetical polypeptide to plasma kallikrein, tenascin and blood coagulation factors.

Cloning and expression in Escherichia coli of cDNAs encoding a 31-kilodalton surface antigen of Sarcocystis muris

Using polyadenylated RNA isolated from Sarcocystis muris cyst merozoites, we have constructed a cDNA library in the expression vector lambda ZAP. Immunoscreening with monoclonal and polyclonal antibodies directed against a 31-kDa surface antigen of S. muris [1] yielded a number of clones with insert sizes ranging between 1.1 kb and 1.3 kb. An additional clone with an insert length of 1.55 kb was isolated by screening with a labeled DNA probe derived from one of the cDNA clones. The cDNA sequence was found to contain an open reading frame specifying a polypeptide of 280 amino acids with a predicted size of 29.7 kDa. The deduced amino acid sequence is rich in serine and threonine (22%) and harbors a hypothetical N-terminal signal peptide sequence as well as a C-terminal glycosyl phosphatidylinositol anchor attachment site. The predicted amino acid sequence has been confirmed by peptide sequencing and an analysis of the overall amino acid composition of the 31-kDa protein. A recombinant protein was obtained which was recognized by the polyclonal antibodies directed against the 31-kDa antigen. Antiserum raised against the purified fusion protein specifically reacted with a 31-kDa protein from S. muris cystozoites. Southern blot analysis indicated that the corresponding gene exists as a single copy within the S. muris genome.