Large proteins have a great tendency to aggregate but a low propensity to form amyloid fibrils.
The assembly of soluble proteins into ordered fibrillar aggregates with cross-β structure is an essential event of many human diseases. The polypeptides undergoing aggregation are generally small in size. To explore if the small size is a primary determinant for the formation of amyloids under pathological conditions we have created two databases of proteins, forming amyloid-related and non-amyloid deposits in human diseases, respectively. The size distributions of the two protein populations are well separated, with the systems forming non-amyloid deposits appearing significantly larger. We have then investigated the propensity of the 486-residue hexokinase-B from Saccharomyces cerevisiae (YHKB) to form amyloid-like fibrils in vitro. This size is intermediate between the size distributions of amyloid and non-amyloid forming proteins. Aggregation was induced under conditions known to be most effective for amyloid formation by normally globular proteins: (i) low pH with salts, (ii) pH 5.5 with trifluoroethanol. In both situations YHKB aggregated very rapidly into species with significant β-sheet structure, as detected using circular dichroism and X-ray diffraction, but a weak Thioflavin T and Congo red binding. Moreover, atomic force microscopy indicated a morphology distinct from typical amyloid fibrils. Both types of aggregates were cytotoxic to human neuroblastoma cells, as indicated by the MTT assay. This analysis indicates that large proteins have a high tendency to form toxic aggregates, but low propensity to form regular amyloid in vivo and that such a behavior is intrinsically determined by the size of the protein, as suggested by the in vitro analysis of our sample protein.
Dipartimento di Scienze Biochimiche, Università di Firenze, Florence, Italy.
Hassan
H
Ramshini
Claudia
C
Parrini
Annalisa
A
Relini
Mariagioia
M
Zampagni
Benedetta
B
Mannini
Alessandra
A
Pesce
Ali Akbar
AA
Saboury
Mohsen
M
Nemat-Gorgani
Fabrizio
F
Chiti
D000682:Amyloid / Q000096:biosynthesis*; D045744:Cell Line, Tumor; D006593:Hexokinase / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008970:Molecular Weight; D009447:Neuroblastoma / Q000473:pathology; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry* / Q000633:toxicity; D029701:Saccharomyces cerevisiae Proteins; D012995:Solubility
D000682:Amyloid; D011506:Proteins; D029701:Saccharomyces cerevisiae Proteins; D006593:Hexokinase
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