Giardia duodenalis Assemblage A Quantitative Proteomics

Giardia duodenalis is a protozoan parasite of a wide range of vertebrates and one of the leading causes of gastroenteritis worldwide. G. duodenalis is a species complex of 8 assemblages with the zoonotic assemblage A as one of two discrete subtypes that is infective for humans. With increasing genomic and transcriptomic data now publicly available through the centralised giardiaDB.org, we have quantitatively analysed the proteomes of 8 G. duodenalis assemblage A strains (7 A1 and 1 A2) to provide a comprehensive proteomic baseline to complement these studies. Protein analysis identified a non-redundant total of 1220 proteins with an average of 764 proteins in each strain. At least 10% of all proteins identified were from the 4 protein families in the G. duodenalis variable genome, and substantial differences in number and abundance profiles in the Variable Surface Protein (VSP) family was observed. We also searched the 8 strains against both assemblage A genomes (subassemblage A1 and A2 genomes) and showed losses in protein identifications, especially for protein identifications associated with Giardia variable gene families which are sub-assemblage specific. We observed two expression profiles of VSPs within Giardia, which was independent to host origin, subassemblage, geographic origin and introduction to axenic culture and may indicate variation in surface antigen switching events and population heterogeneity. We hypothesise this variation may be related to karotype and chromosomal variation, which would indicate an assemblage-independent mechanism of variation in G. duodenalis.