Comprehensive proteome analysis of propolis elucidates the origin and function of its proteins

Propolis is a resinous honeybee product, rich in polyphenolic compounds and with high economic value. Although extensive studies regarding the chemical composition of different propolis extracts have been carried out, the propolis proteome remained unknown. The present study aimed at characterizing the proteome of two geographically-distinct propolis originating from Belgium and Iran. Propolis extracts were analysed by SDS-PAGE followed by MALDI-TOF MS (mass spectrometry) and LC-ESI-MS. Our in-depth proteomic analysis led to the identification of honeybee venom and royal jelly proteins, and numerous plant-defense proteins in propolis, extending our understanding on the antimicrobial properties of this complex natural substance. The proteome of both propolis was mainly made up of proteins belonging to the poplar tree. The poplar PR-2 (β-1,3-glucanases) and PR-8 (acidic endochitinases) proteins were found to be the major components of both propolis extracts, while bee venom (Api m 1) and royal jelly allergens (MJRP 1 and 2) were only identified in the propolis from Belgium. Overall, our proteome analyses revealed that propolis extracts from Belgium and Iran shared a core protein composition originating from the poplar proteome. The majority of identified proteins are involved in the plant defense against pathogens, some belonging to well-known pathogenesis-related families.