title: Conformational flexibility of a human immunoglobulin light chain variable domain by relaxation dispersion nuclear magnetic resonance spectroscopy: implications for protein misfolding and amyloid assembly.
abstract: The conformational flexibility of a human immunoglobulin κIV light-chain variable domain, LEN, which can undergo conversion to amyloid under destabilizing conditions, was investigated at physiological and acidic pH on a residue-specific basis by multidimensional solution-state nuclear magnetic resonance (NMR) methods. Measurements of backbone chemical shifts and amide (15)N longitudinal and transverse spin relaxation rates and steady-state nuclear Overhauser enhancements indicate that, on the whole, LEN retains its native three-dimensional fold and dimeric state at pH 2 and that the protein backbone exhibits limited fast motions on the picosecond to nanosecond time scale. On the other hand, (15)N Carr--Purcell--Meiboom--Gill (CPMG) relaxation dispersion NMR data show that LEN experiences considerable slower, millisecond time scale dynamics, confined primarily to three contiguous segments of about 5-20 residues and encompassing the N-terminal β-strand and complementarity determining loop regions 2 and 3 in the vicinity of the dimer interface. Quantitative analysis of the CPMG relaxation dispersion data reveals that at physiological pH these slow backbone motions are associated with relatively low excited-state protein conformer populations, in the ~2-4% range. Upon acidification, the minor conformer populations increase significantly, to ~10-15%, with most residues involved in stabilizing interactions across the dimer interface displaying increased flexibility. These findings provide molecular-level insights about partial protein unfolding at low pH and point to the LEN dimer dissociation, initiated by increased conformational flexibility in several well-defined regions, as being one of the important early events leading to amyloid assembly.
authors.affiliation: Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, United States.
authors.forename: Sujoy
authors.initials: S
authors.lastname: Mukherjee
authors.forename: Simon P
authors.initials: SP
authors.lastname: Pondaven
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Jaroniec
mesh_terms: D001536:Bence Jones Protein / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007147:Immunoglobulin Light Chains / Q000737:chemistry* / Q000378:metabolism; D007135:Immunoglobulin Variable Region / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D009068:Movement; D009101:Multiple Myeloma; D019906:Nuclear Magnetic Resonance, Biomolecular; D017510:Protein Folding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary
chemical_list: D007147:Immunoglobulin Light Chains; D007135:Immunoglobulin Variable Region; D001536:Bence Jones Protein