Screening for glycosylphosphatidylinositol-anchored proteins in the Paracoccidioides brasiliensis transcriptome

ABSTRACT

Open reading frames in the transcriptome of Paracoccidioides brasiliensis were screened for potential glycosylphosphatidylinositol (GPI)-anchored proteins, which are a functionally and structurally diverse family of post-translationally modified molecules found in a variety of eukaryotic cells. Numerous studies have demonstrated that various GPI anchor sequences can affect the localization of these proteins in the plasma membrane or the cell wall. The GPI anchor core is produced in the endoplasmic reticulum by sequential addition of monosaccharides and phospho-ethanolamine to phosphatidylinositol. The complete GPI anchor is post-translationally attached to the protein carboxyl-terminus by GPI transamidases. Removal of this GPI lipid moiety by phospholipases generates a soluble form of the protein. The identification of putative GPI-attached proteins in the P. brasiliensis transcriptome was based on the following criteria the presence of an N-terminal signal peptide for secretion and a hydrophobic region in the C-terminus presenting the GPI-attachment site. The proteins that were identified were in several functional categories i) eight proteins were predicted to be enzymes (Gel1, Gel2, Gel3, alpha-amylase, aspartic proteinase, Cu-Zn SOD, DFG5, PLB); ii) Ag2/PRA, ELI-Ag1 and Gel1 are probably surface antigens; iii) Crh-like and the GPI-anchored cell wall protein have a putative structural role; iv) ECM33 and Gels (1, 2 and 3) are possibly involved in cell wall biosynthesis, and v) extracellular matrix protein is considered to be an adhesion protein. In addition, eight deduced proteins were predicted to localize in the plasma membrane and six in the cell wall. We also identified proteins involved in the synthesis, attachment and cleaving of the GPI anchor in the P. brasiliensis transcriptome.