Abstract
Three variants of human beta(2)-microglobulin (beta(2)-m) were compared with wild-type protein. For two variants, namely the mutant R3Abeta(2)-m and the form devoid of the N-terminal tripeptide (DeltaN3beta(2)-m), a reduced unfolding free energy was measured compared with wild-type beta(2)-m, whereas an increased stability was observed for the mutant H31Ybeta(2)-m. The solution structure could be determined by (1)H NMR spectroscopy and restrained modeling only for R3Abeta(2)-m that showed the same conformation as the parent species, except for deviations at the interstrand loops. Analogous conclusions were reached for H31Ybeta(2)-m and DeltaN3beta(2)-m. Precipitation and unfolding were observed over time periods shorter than 4-6 weeks with all the variants and, sometimes, with wild-type protein. The rate of structured protein loss from solution as a result of precipitation and unfolding always showed pseudo-zeroth order kinetics. This and the failure to observe an unfolded species without precipitation suggest that a nucleated conformational conversion scheme should apply for beta(2)-m fibrillogenesis. The mechanism is consistent with the previous and present results on beta(2)-m amyloid transition, provided a nucleated oligomeric species be considered the stable intermediate of fibrillogenesis, the monomeric intermediate being the necessary transition step along the pathway from the native protein to the nucleated oligomer.
Highlights
Over the last several years, an overwhelming number of reports have addressed the phenomenon of amyloidogenesis
guanidinium chloride (GdmCl) Denaturation—The denaturation of wild-type and variant 2-m species was measured from the changes in fluorescence upon addition of GdmCl, and the results are presented in Table I and Fig. 1. ⌬N62-m appears to be the least stable species followed by ⌬N32-m and R3A2-m, which show intermediate ⌬G° and Cm values between wild type and ⌬N62-m
The nucleated conformational conversion (NCC) mechanism, which was demonstrated for Alzheimer A peptide [49, 52] and Sup35 NM domain [50] and proposed as the most general and reliable scheme for amyloidogenesis [51], seems to apply to 2-m fibril formation
Summary
Over the last several years, an overwhelming number of reports have addressed the phenomenon of amyloidogenesis. We determined the solution structure of isolated 2-m by NMR spectroscopy [5] and showed that the most important rearrangements of the protein, with respect to its structure in MHC-I, were observed for strands D and E, interstrand loop D-E, and strand A, including the N-terminal segment We stated that these modifications can be considered as the prodromes of the amyloid transition that starts at sheet 1 with the rupture of strand A pairing, and leads to polymerization, through intermolecular pairing at strand D and probably strand C, and precipitation into fibrils, i.e. according to the scheme we had proposed earlier from a comparative investigation on the full-length protein and the form devoid of the six N-terminal residues (⌬N62-m) [6]. An arginyl and a histidyl residue, respectively, are replaced with an alanyl and a tyrosyl residue, respectively
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
