SAPs, pepsin-like proteinases secreted from pathogens to degrade host proteins.
SAPs (Secreted aspartic proteinases) are secreted from a group of pathogenic fungi, predominantly Candida species. They are secreted from the pathogen to degrade host proteins. SAP is one of the most significant extracellular hydrolytic enzymes produced by C. albicans. SAP proteins, encoded by a family of 10 SAP genes. All 10 SAP genes of C. albicans encode preproenzymes, approximately 60 amino acid longer than the mature enzyme, which are processed when transported via the secretory pathway. The mature enzymes contain sequence motifs typical for all aspartyl proteinases, including the two conserved aspartate residues other active site and conserved cysteine residues implicated in the maintenance of the three-dimensional structure. Most Sap proteins contain putative N-glycosylation sites, but it remains to be determined which Sap proteins are glycosylated. This family of aspartate proteases is classified by MEROPS as the peptidase family A1 (pepsin A, clan AA). The overall structure of Sap protein conforms to the classical aspartic proteinase fold typified by pepsin. SAP is a bilobal enzyme, each lobe contributing a catalytic Asp residue, with an extended active site cleft localized between the two lobes of the molecule. One lobe may be evolved from the other through ancient gene-duplication event. More recently evolved enzymes have similar three-dimensional structures, however their amino acid sequences are more divergent except for the conserved catalytic site motif. This family of aspartate proteases is classified by MEROPS as the peptidase family A1 (pepsin A, clan AA).