A developmentally regulated gene of trypanosomes encodes a homolog of rat protein-disulfide isomerase and phosphoinositol-phospholipase C

Abstract

We have isolated and characterized a developmentally regulated gene in Trypanosoma brucei, arbitrarily termed BS2. BS2 mRNA is substantially more abundant in bloodstream-form trypanosomes than in procyclic culture forms. Its nucleotide sequence reveals a single contiguous open-reading frame of 497 codons and is predicted to encode a protein of approximately 55.5 kilodaltons. A search of the NBRF protein data base revealed that within the predicted amino acid sequence are two of the evolutionarily conserved redox sites typified by thioredoxin of bacteria. Of this family of proteins, the recently sequenced rat genes encoding protein-disulfide isomerase (PDI) and form I phosphoinositide-specific phospholipase C (PIPLC) showed homology extending over the length of all three proteins (i.e., between BS2, PDI, and PIPLC). Although this homology includes the acidic C-terminus characteristic of proteins localized to the lumen of the endoplasmic reticulum, the BS2 product is predicted to possess multiple sites for N-linked glycosylation while PDI and PIPLC have none. Possible roles of the BS2 gene product in trypanosome physiology are discussed.

Characterization of Two Protein Disulfide Isomerases from the Endocytic Pathway of Bloodstream Forms of Trypanosoma brucei

“…3A). These results were in agreement with those of Hsu et al (9), who observed a 15-fold down-regulation of the BS2 mRNA in procyclic forms. Western blot analysis, using polyclonal antibodies raised against the recombinant proteins, demonstrated directly that both Tb-PDI-1 and TbPDI-2 were expressed only in bloodstream forms (Fig.…”

“…In other eukaryotes, lysosomal enzymes are routed to endosomes by a mannose 6-phosphate receptor that interacts in a reversible manner with phosphorylated mannose residues on N-glycans of the cargo protein (50). Interestingly, in a prescient comment, Hsu et al (9) observed that the number of …”

“…1B). TbPDI-2 was encoded by a full-length cDNA (ϳ2 kb) that coded for a polypeptide of 497 residues with a predicted molecular mass of 55 kDa and a pI of 5.3 and was identical to the BS2 gene product described by Hsu et al (9). TbPDI-2 contained two double-cysteine, redox-active sites located at the C-and N-terminal regions of the protein and separated by 224 residues (Fig.…”

“…Interestingly, two cDNAs were abundant among the clones selected and appeared to code for two distinct protein disulfide isomerases (PDIs). 1 One of these cDNAs was originally identified 15 years ago by Hsu et al (9) as part of their studies on gene expression in trypanosomes, but the putative PDI was not characterized. The PDIs are thiol-disulfide oxidoreductases that catalyze the formation, reduction, and isomerization of disulfide bonds, depending on the redox environment, and can also function as molecular chaperones, in which they assist in the folding of proteins (10 -12).…”

Intracellular Trafficking and Glycobiology of TbPDI2, a Stage-Specific Protein Disulfide Isomerase in Trypanosoma brucei

“…Critical to this function is the presence of one or two thioredoxin-like domains. The T. brucei genome encodes five putative PDI genes, one of which, TbPDI2 (Tb927.10.8230; initially known as BS2), is specifically upregulated in the BSF stage of the life cycle (5,16). TbPDI2 contains two thioredoxin-like domains and is unusual in that it has 12 potential N-glycosylation sites.…”