Anti-amyloidogenic property of human gastrokine 1

Gastrokine 1 (GKN1) is a stomach-specific protein expressed in normal gastric tissue but absent in gastric cancer. GKN1 plays a major role in maintaining gastric mucosa integrity and is characterized by the presence of a BRICHOS domain consisting of about 100 amino acids also found in several unrelated proteins associated with major human diseases like BRI2, related to familial British and Danish dementia and surfactant protein C (SP-C), associated with respiratory distress syndrome. It was reported that recombinant BRICHOS domains from BRI2 and SP-C precursor (proSP-C) prevent fibrils formation of amyloid-beta peptide (Aβ), that is the major component of extracellular amyloid deposits in Alzheimer's disease. Here we investigated on the interaction between human recombinant GKN1 (rGKN1) and Aβ peptide (1-40) that derives from the partial hydrolysis of the amyloid precursor protein (APP). GKN1 prevented amyloid aggregation and fibrils formation by inhibiting Aβ(1-40) polymerization, as evaluated by SDS-PAGE, thioflavin-T binding assay and gel filtration experiments. Mass spectrometry showed the formation of a prevailing 1:1 complex between GKN1 and Aβ(1-40). SPR analysis of GKN1/Aβ interaction led to calculate a dissociation constant (K_D) of 34 μM. Besides its interaction with Aβ(1-40), GKN1 showed also to interact with APP as evaluated by confocal microscopy and Ni-NTA pull-down. Data strongly suggest that GKN1 has anti-amyloidogenic properties thus functioning as a chaperone directed against unfolded segments and with the ability to recognize amyloidogenic polypeptides and prevent their aggregation.