title: 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.
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.
authors.affiliation: Dipartimento di Scienze e Tecnologie Biomediche and MATI Centre of Excellence, University of Udine, Italy.
authors.forename: Maria C
authors.initials: MC
authors.lastname: Mimmi
authors.forename: Thomas J D
authors.initials: TJ
authors.lastname: Jørgensen
authors.forename: Fabio
authors.initials: F
authors.lastname: Pettirossi
authors.forename: Alessandra
authors.initials: A
authors.lastname: Corazza
authors.forename: Paolo
authors.initials: P
authors.lastname: Viglino
authors.forename: Gennaro
authors.initials: G
authors.lastname: Esposito
authors.forename: Ersilia
authors.initials: E
authors.lastname: De Lorenzi
authors.forename: Sofia
authors.initials: S
authors.lastname: Giorgetti
authors.forename: Mette
authors.initials: M
authors.lastname: Pries
authors.forename: Dorthe B
authors.initials: DB
authors.lastname: Corlin
authors.forename: Mogens H
authors.initials: MH
authors.lastname: Nissen
authors.forename: Niels H H
authors.initials: NH
authors.lastname: Heegaard
mesh_terms: D019075:Electrophoresis, Capillary; D006801:Humans; D007669:Kidney Calculi / Q000628:therapy / Q000652:urine; D008239:Lysine; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008958:Models, Molecular; D011487:Protein Conformation; D017582:Renal Replacement Therapy; D013816:Thermodynamics; D001613:beta 2-Microglobulin / Q000737:chemistry* / Q000302:isolation & purification / Q000652:urine
chemical_list: D001613:beta 2-Microglobulin; D008239:Lysine