Variants of beta-microglobulin cleaved at lysine-58 retain the main conformational features of the native protein but are more conformationally heterogeneous and unstable at physiological temperature

FEBS J. 2006 Jun;273(11):2461-74. doi: 10.1111/j.1742-4658.2006.05254.x.

Abstract

Cleavage of the small amyloidogenic protein beta2-microglobulin after lysine-58 renders it more prone to unfolding and aggregation. This is important for dialysis-related beta2-microglobulin amyloidosis, since elevated levels of cleaved beta2-microglobulin may be found in the circulation of dialysis patients. However, the solution structures of these cleaved beta2-microglobulin variants have not yet been assessed using single-residue techniques. We here use such methods to examine beta2-microglobulin cleaved after lysine-58 and the further processed variant (found in vivo) from which lysine-58 is removed. We find that the solution stability of both variants, especially of beta2-microglobulin from which lysine-58 is removed, is much reduced compared to wild-type beta2-microglobulin and is strongly dependent on temperature and protein concentration. 1H-NMR spectroscopy and amide hydrogen (1H/2H) exchange monitored by MS show that the overall three-dimensional structure of the variants is similar to that of wild-type beta2-microglobulin at subphysiological temperatures. However, deviations do occur, especially in the arrangement of the B, D and E beta-strands close to the D-E loop cleavage site at lysine-58, and the experiments suggest conformational heterogeneity of the two variants. Two-dimensional NMR spectroscopy indicates that this heterogeneity involves an equilibrium between the native-like fold and at least one conformational intermediate resembling intermediates found in other structurally altered beta2-microglobulin molecules. This is the first single-residue resolution study of a specific beta2-microglobulin variant that has been found circulating in dialysis patients. The instability and conformational heterogeneity of this variant suggest its involvement in beta2-microglobulin amyloidogenicity in vivo.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Electrophoresis, Capillary
  • Humans
  • Kidney Calculi / therapy
  • Kidney Calculi / urine
  • Lysine*
  • Magnetic Resonance Spectroscopy
  • Mass Spectrometry
  • Models, Molecular
  • Protein Conformation
  • Renal Replacement Therapy
  • Thermodynamics
  • beta 2-Microglobulin / chemistry*
  • beta 2-Microglobulin / isolation & purification
  • beta 2-Microglobulin / urine

Substances

  • beta 2-Microglobulin
  • Lysine