Dynamic of β2-Microglobulin Fibril Formation and Reabsorption: The Role of Proteolysis

Authors

  • Vittorio Bellotti,

    1. Department of Biochemistry University of Pavia, Pavia, Italy,
    2. Biotechnological Laboratories IRCCS Policlinico San Matteo, Pavia, Italy,
    3. Centro per lo Studio e la Cura delle Amiloidosi, Pavia, Italy, and
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  • Maurizio Gallieni,

    1. Department of Nephrology, San Paolo Hospital, Milan, Italy
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  • Sofia Giorgetti,

    1. Department of Biochemistry University of Pavia, Pavia, Italy,
    2. Biotechnological Laboratories IRCCS Policlinico San Matteo, Pavia, Italy,
    3. Centro per lo Studio e la Cura delle Amiloidosi, Pavia, Italy, and
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  • Diego Brancaccio

    1. Department of Nephrology, San Paolo Hospital, Milan, Italy
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Address correspondence to: Diego Brancaccio, MD, Department of Nephrology, Ospedale San Paolo, Via Di Rudinì 8, 20142 Milan, Italy. E-mail: diego.brancaccio@tiscalinet.it.

ABSTRACT

Dialysis-related amyloidosis (DRA) is caused by the deposition, in target tissues, of β2-microglobulin (β2M) in fibrillar conformation. Several reports indicate that fibrillar β2M is chemically heterogeneous and such heterogeneity is partially related to the presence of truncated species of the protein. In association with the full-length species, a β2M isoform lacking six N-terminal residues is present in all the samples of our collection of ex vivo fibrils. The pattern of proteolytic cleavage in amyloidosis and in other diseases is completely different, as demonstrated by the absence in fibrillar β2M of the cleavage at lysine 58, which is contrary to that described in rheumatoid arthritis and other diseases. The role of limited proteolysis of β2M in the pathogenesis of the disease is uncertain. However, we have shown that the apparently minor modification of the intact protein, such as the removal of N-terminal hexapeptide, is capable of dramatically affecting its stability, protection from proteolytic digestion, and enhance its capacity to make in vitro amyloid fibrils. The structure, folding dynamic, and function of the truncated species of β2M, peculiar of DRA, could shed new light on the mechanism of β2M fibril formation and reabsorption.

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