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Homogentisic acid induces aggregation and fibrillation of amyloidogenic proteins

2016; Elsevier BV; Volume: 1861; Issue: 2 Linguagem: Inglês

10.1016/j.bbagen.2016.11.026

1872-8006

Daniela Braconi, Lia Millucci, Andrea Bernini, Ottavia Spiga, Pietro Lupetti, Barbara Marzocchi, Neri Niccolai, Giulia Bernardini, Annalisa Santucci,

Biochemical Acid Research Studies

Alkaptonuria (AKU) is an ultra-rare inborn error of metabolism characterized by homogentisic acid (HGA) accumulation due to a deficient activity of the homogentisate 1.2-dioxygenase (HGD) enzyme. This leads to the production of dark pigments that are deposited onto connective tissues, a condition named 'ochronosis' and whose mechanisms are not completely clear. Recently, the potential role of hitherto unidentified proteins in the ochronotic process was hypothesized, and the presence of Serum Amyloid A (SAA) in alkaptonuric tissues was reported, allowing the classification of AKU as a novel secondary amyloidosis.Gel electrophoresis, Western Blot, Congo Red-based assays and electron microscopy were used to investigate the effects of HGA on the aggregation and fibrillation propensity of amyloidogenic proteins and peptides [Aβ(1-42), transthyretin, atrial natriuretic peptide, α-synuclein and SAA]. LC/MS and in silico analyses were undertaken to identify possible binding sites for HGA (or its oxidative metabolite, a benzoquinone acetate or BQA) in SAA.We found that HGA might act as an amyloid aggregation enhancer in vitro for all the tested proteins and peptides in a time- and dose- dependent fashion, and identified a small crevice at the interface between two HGD subunits as a candidate binding site for HGA/BQA.HGA might be an important amyloid co- component playing significant roles in AKU amyloidosis.Our results provide a possible explanation for the clinically verified onset of amyloidotic processes in AKU and might lay the basis to setup proper pharmacological approaches to alkaptonuric ochronosis, which are still lacking.