title: Echinococcus granulosus antigen B structure: subunit composition and oligomeric states.
abstract: BACKGROUND
  Antigen B (AgB) is the major protein secreted by the Echinococcus granulosus metacestode and is involved in key host-parasite interactions during infection. The full comprehension of AgB functions depends on the elucidation of several structural aspects that remain unknown, such as its subunit composition and oligomeric states.
  
  
  RESULTS
  The subunit composition of E. granulosus AgB oligomers from individual bovine and human cysts was assessed by mass spectrometry associated with electrophoretic analysis. AgB8/1, AgB8/2, AgB8/3 and AgB8/4 subunits were identified in all samples analyzed, and an AgB8/2 variant (AgB8/2v8) was found in one bovine sample. The exponentially modified protein abundance index (emPAI) was used to estimate the relative abundance of the AgB subunits, revealing that AgB8/1 subunit was relatively overrepresented in all samples. The abundance of AgB8/3 subunit varied between bovine and human cysts. The oligomeric states formed by E. granulosus AgB and recombinant subunits available, rAgB8/1, rAgB8/2 and rAgB8/3, were characterized by native PAGE, light scattering and microscopy. Recombinant subunits showed markedly distinct oligomerization behaviors, forming oligomers with a maximum size relation of rAgB8/3>rAgB8/2>rAgB8/1. Moreover, the oligomeric states formed by rAgB8/3 subunit were more similar to those observed for AgB purified from hydatid fluid. Pressure-induced dissociation experiments demonstrated that the molecular assemblies formed by the more aggregative subunits, rAgB8/2 and rAgB8/3, also display higher structural stability.
  
  
  CONCLUSIONS
  For the first time, AgB subunit composition was analyzed in samples from single hydatid cysts, revealing qualitative and quantitative differences between samples. We showed that AgB oligomers are formed by different subunits, which have distinct abundances and oligomerization properties. Overall, our findings have significantly contributed to increase the current knowledge on AgB expression and structure, highlighting issues that may help to understand the parasite adaptive response during chronic infection.
authors.affiliation: Laboratório de Biologia Molecular de Cestódeos and Laboratório de Genômica Estrutural e Funcional, Centro de Biotecnologia, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil.
authors.forename: Karina M
authors.initials: KM
authors.lastname: Monteiro
authors.forename: Mateus B
authors.initials: MB
authors.lastname: Cardoso
authors.forename: Cristian
authors.initials: C
authors.lastname: Follmer
authors.forename: Nádya P
authors.initials: NP
authors.lastname: da Silveira
authors.forename: Daiani M
authors.initials: DM
authors.lastname: Vargas
authors.forename: Elliot W
authors.initials: EW
authors.lastname: Kitajima
authors.forename: Arnaldo
authors.initials: A
authors.lastname: Zaha
authors.forename: Henrique B
authors.initials: HB
authors.lastname: Ferreira
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D004443:Echinococcosis / Q000469:parasitology; D004586:Electrophoresis; D006801:Humans; D008074:Lipoproteins / Q000737:chemistry* / Q000302:isolation & purification; D013058:Mass Spectrometry; D008853:Microscopy; D008969:Molecular Sequence Data; D055503:Protein Multimerization; D021122:Protein Subunits / Q000737:chemistry; D017386:Sequence Homology, Amino Acid
chemical_list: D008074:Lipoproteins; D021122:Protein Subunits; C514022:antigen B, Echinococcus granulosus