β2-Microglobulin, a 12 kDa protein forming part of the class I HLA (histocompatibility locus antigen) major histocompatibility complex, has been used as a prognosis factor for multiple myeloma and as a marker of renal function, and has been shown to be involved in the pathogenesis of dialysis-related amyloidosis. α2-Macroglobulin has the ability to bind a wide range of physiologically important molecules, thereby influencing their metabolic impact. In this study we show by Western blotting analysis that β2-microglobulin binds to α2-macroglobulin in vitro. This binding was confirmed by BIAcore analysis, and was shown by ELISA to be concentration-dependent. The sequences of the binding peptides in the mature β2-microglobulin molecule were identified by Spot multiple peptide synthesis and α2-macroglobulin binding studies. In conclusion, β2-microglobulin interacts specifically with the universal antiprotease a2-macroglobulin. The identification of this interaction brings into question some of the axioms on the metabolism of β2-microglobulin, and may help to explain the clinical findings observed in b2-microglobulin-related diseases.

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