Properties of some variants of human beta2-microglobulin and amyloidogenesis.
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.
Corazza
Alessandra
A
Dipartimento di Scienze e Tecnologie Biomediche and Microgravity, Aging, Training, and Immobility, Centre of Excellence, Università di Udine, Piazzale Kolbe 4, 33100 Udine, Italy.
Pettirossi
Fabio
F
Viglino
Paolo
P
Verdone
Giuliana
G
Garcia
Julian
J
Dumy
Pascal
P
Giorgetti
Sofia
S
Mangione
Palma
P
Raimondi
Sara
S
Stoppini
Monica
M
Bellotti
Vittorio
V
Esposito
Gennaro
G
D000682:Amyloid / Q000378:metabolism; D000686:Amyloidosis / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D009154:Mutation; D011487:Protein Conformation; D011489:Protein Denaturation; D013329:Structure-Activity Relationship; D001613:beta 2-Microglobulin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D000682:Amyloid; D001613:beta 2-Microglobulin