Quantitative proteomic analysis of Giardia duodenalis assemblage A: A baseline for host, assemblage, and isolate variation

Abstract

Giardia duodenalis is a gastrointestinal protozoan parasite of vertebrates and is a species complex comprised of eight assemblages, with the zoonotic assemblage A one of two subtypes infective for humans. With increasing genomic and transcriptomic data publicly available through the centralized giardiaDB.org, we have quantitatively analyzed the proteomes of eight G. duodenalis assemblage A strains (seven A1 and one A2) to provide a proteomic baseline to complement the available data. A nonredundant total of 1197 subassemblage A1 proteins and 719 subassemblage A2 proteins were identified with an average of 770 proteins in each strain. The eight strains were also searched against both assemblage A genome sequences (subassemblage A1 and A2 genomes) and demonstrated subassemblage specific differences in protein identifications, especially for variable gene families. Substantial differences were observed in the numbers and abundance in the variable surface protein family, and two different variable surface protein expression profiles that were independent of host origin, subassemblage, or geographic origin. We hypothesize that this variation in surface antigen switching events may be related to karotype and chromosomal variation, which would indicate an assemblage-independent mechanism of diversity generation in G. duodenalis. All MS data have been deposited in the ProteomeXchange with identifier PXD001272 (http://proteomecentral.proteomexchange.org/dataset/PXD001272).

Giardia secretome highlights secreted tenascins as a key component of pathogenesis

“…S2). This represents more than a quarter of the open reading frames predicted by the respective genomes in this single life cycle stage under this steady state set of in vitro culture conditions and compares favourably with other recent proteomic analyses of Giardia [17, 18]. Lists of proteins detected in only 1 of the 2 assemblages are provided (Additional file 2: Tables S1 and S2).…”

The generation gap: Proteome changes and strain variation during encystation in Giardia duodenalis

“…In total, there were 2 large functional clusters that varied between strains and life cycle stages; 'VSP/Furin-like/EGFlike' and 'ankyrin-repeat'. Both these clusters feature proteins from the Giardia variable genome already implicated in inter-and intra-assemblage variation [23,49,51]. These data reinforce the hypothesis that the diversity seen in such families at the genome level translates to crucial differences at the level of the expressed proteome between strains at both life cycle stages.…”

“…Intra-assemblage variation within G. duodenalis is yet to be comprehensively analysed since genomes have become available, although it has been shown that Giardia-specific gene families of the variable genome differ between assemblages [49,50]. Protein expression of VSP variants also varies between cultured trophozoites from multiple strains of the same subassemblage [51]. Between the 488 and the 688 reproducibly identified proteins in H-106 and B-2041 cysts, 373 proteins were common, which corresponds to 76.4% of cyst proteins from H-106 and 54.2% of proteins from B-2041 cysts (Fig.…”

“…Nonetheless, though the biological significance of differential protein 21.1 expression between H-106 and B-2041 remains unclear, it is a point of considerable strain variation. It remains to be investigated what the targets and the functions of this large class of proteins are in G. duodenalis, of which many members are also constitutively expressed [6,23,51].…”

“…In G. duodenalis post-transcriptional regulations means only a single VSP is expressed on the entirety of the parasite surface [54], and in axenic culture the absence of immune selection allows multiple VSP variants in the population to proliferate, which are detected in proteomics [6,23,51]. Though microRNAs (miRNAs) derived from small nucleolar RNAs (snoRNAS) play a role in VSP-switching [55] it is not confirmed experimentally if exogenous signals from environment, media or host affect the proliferation and survival of some VSP variants.…”