A beta2-microglobulin cleavage variant fibrillates at near-physiological pH

Area of Science:

• Biochemistry
• Molecular Biology
• Medical Science

Background:

• Dialysis-related amyloidosis (DRA) involves beta2-microglobulin (beta2m) deposits, primarily in joints.
• The molecular basis of beta2m's amyloidogenicity remains largely undetermined.
• Native beta2m requires highly acidic conditions (pH < 4.5) for in vitro amyloid fibrillation over several days.

Purpose of the Study:

• To investigate the amyloid formation potential of a circulating beta2m variant found in dialysis patients.
• To determine the conditions under which this beta2m variant can form amyloid fibrils.
• To explore the seeding capacity of the variant's amyloid fibrils on native beta2m.

Main Methods:

• Utilized Thioflavin T fluorescence spectroscopy to monitor fibrillation.
• Employed turbidimetry to assess protein aggregation.
• Applied capillary electrophoresis and electron microscopy for detailed analysis of fibril formation and structure.

Main Results:

• A cleavage variant of beta2m, prevalent in dialysis patients, rapidly forms amyloid fibrils within an hour at pH 6.6.
• This pH level (6.6) is physiologically relevant, occurring in joints during inflammation.
• Pre-formed fibrils of the beta2m variant efficiently induced fibrillation of native beta2m, even in small quantities.

Conclusions:

• A biologically relevant variant of beta2m exhibits significant amyloidogenicity at slightly acidic pH levels.
• The rapid fibrillation of the beta2m variant at physiological pH may explain its deposition in joints in DRA.
• The potent seeding activity of the variant's fibrils suggests a mechanism for the progression of amyloidosis in dialysis patients.