When the GenBank Hyal amino acid sequence for Pp-Hyal (ADLO9135) from this study was aligned with the same allergen of V.

vulgaris (PDB 2ATM), P. annularis (HUGA_POLAN), and A. mellifera (PDB 1FCQ_A), high levels of similarity were revealed (75%, 90%, and 54%, respectively). In Fig. 2, shaded blue areas indicate several regions of similarity mainly among the three first molecules. In addition, the amino acids DFE (highlighted by a red rectangle), which are present in the active site, are also highly conserved. The two proteins – Ves v 2 (PDB ID: 2ATM) and Api m 2 (PDB ID: 1FCQ) – used for building the model of the 3D-structure of the Pp-Hyal had their 3D-structures already determined by X-ray crystallography at a resolution of 2.0 Å ( Skov et al., 2006) and 2.7 Å ( Markovic-Housley et al., 2000), respectively. Despite the greater similarity among sequences have been found between PTC124 the proteins of P. paulista and V. vulgaris, only the 3D-structure of the Api m 2 was solved with HA as its substrate, reason why the latter was used in this study to identify the Pp-Hyal active site and points of contact with the substrate. Based on its model (Fig. 3A,B), Pp-Hyal displays a structure comprised of a central barrel (β/α)7 containing seven α-helix and seven beta-sheets, in agreement with the

expected structure for all hyaluronidases DZNeP belonging to family 56 of glycoside hydrolases ( Henrissat and Bairoch, 1996; Markovic-Housley et al., 2000; Skov et al., 2006). This model also reveals two important characteristics of the Pp-Hyal structure: the presence of two disulfide bonds between Cys 19–308 and Cys 185–197 ( Fig. 3A) and putative glycosylation sites on residues Asn79, Asn187, and Asn325 ( Fig. 3B). The sites Asn79 (5′ NITI 3′) and Asn325 (5′ NITI 3′) are also found in Hyal of V. vulgaris venom ( Skov et al., 2006), indicating that they exert a direct influence on the immunogenicity of the molecule. Glycosylation is the most common post-translational modification of many eukaryotic intracellular proteins, contributing to biological

activity, immunogenicity, solubility, stability, and protease resistance. second Carbohydrate residues may be enzymatically attached to proteins through the N-glycoside bond via the amide nitrogen of asparagine, or through the O-glycoside bond via the hydroxyl group of serines, threonines, hydroxylysines or hydroxyproline, or by a glycosylphosphatidylinositol anchor, which is subsequently removed ( Steinberg et al., 2001). Fig. 4 shows the topology of the Pp-Hyal molecule ( Fig. 4A), making evident its active site position when compared to that of Hyal from A. mellifera and the predicted amino acid residues in the model that establish interaction with the substrate Ser299, Asp107 and Glu109 ( Fig. 4B).