1H chemical shift assignment for the truncated form of the human
beta2-microglobulin lacking of the first 3 residues

For several residues a second chemical shift is observed, indicating a minor conformational
species (25%).

Properties of some variants of human beta2-microglobulin and amyloidogenesis.

The solution structure of human beta2-microglobulin (beta2-m), the
nonpolymorphic component of class I major histocompatibility complex (MHC-I),
was determined by (1)H NMR spectroscopy and restrained modeling calculations.
Compared to previous structural data obtained from the NMR secondary structure
of the isolated protein and the crystal structure of MHC-I, in which the
protein is associated to the heavy-chain component, several differences are
observed. The most important rearrangements were observed for (1) strands V and
VI (loss of the C-terminal and N-terminal end, respectively), (2) interstrand
loop V-VI, and (3) strand I, including the N-terminal segment (displacement
outward of the molecular core). These modifications can be considered as the
prodromes of the amyloid transition. Solvation of the protected regions in
MHC-I decreases the tertiary packing by breaking the contiguity of the surface
hydrophobic patches at the interface with heavy chain and the nearby region at
the surface charge cluster of the C-terminal segment. As a result, the molecule
is placed in a state in which even minor charge and solvation changes in
response to pH or ionic-strength variations can easily compromise the
hydrophobic/hydrophilic balance and trigger the transition into a partially
unfolded intermediate that starts with unpairing of strand I and leads to
polymerization and precipitation into fibrils or amorphous aggregates. The same
mechanism accounts for the partial unfolding and fiber formation subsequent to
Cu(2+) binding, which is shown to occur primarily at His 31 and involve
partially also His 13, the next available His residue along the partial
unfolding pathway.

Verdone G, Corazza A, Viglino P, Pettirossi F, Giorgetti S, Mangione P, Andreola A,
Stoppini M, Bellotti V, Esposito G.
Protein Sci 2002 11(3):487-99
The solution structure of human beta2-microglobulin reveals the prodromes of its amyloid
transition.

Protein science : a publication of the Protein Society
The solution structure of human beta2-microglobulin reveals the prodromes of its amyloid transition.

The solution structure and stability of N-terminally truncated
beta2-microglobulin (deltaN6beta2-m), the major modification in ex vivo
fibrils, have been investigated by a variety of biophysical techniques. The
results show that deltaN6beta2-m has a free energy of stabilization that is
reduced by 2.5 kcal/mol compared to the intact protein. Hydrogen exchange of a
mixture of the truncated and full-length proteins at microM concentrations at
pH 6.5 monitored by electrospray mass spectrometry reveals that deltaN6beta2-m
is significantly less protected than its wild-type counterpart. Analysis of
deltaN6beta2-m by NMR shows that this loss of protection occurs in beta strands
I, III, and part of II. At mM concentration gel filtration analysis shows that
deltaN6beta2-m forms a series of oligomers, including trimers and tetramers,
and NMR analysis indicates that strand V is involved in intermolecular
interactions that stabilize this association. The truncated species of
beta2-microglobulin was found to have a higher tendency to self-associate than
the intact molecule, and unlike wild-type protein, is able to form amyloid
fibrils at physiological pH. Limited proteolysis experiments and analysis by
mass spectrometry support the conformational modifications identified by NMR
and suggest that deltaN6beta2-m could be a key intermediate of a proteolytic
pathway of beta2-microglobulin. Overall, the data suggest that removal of the
six residues from the N-terminus of beta2-microglobulin has a major effect on
the stability of the overall fold. Part of the tertiary structure is preserved
substantially by the disulfide bridge between Cys25 and Cys80, but the pairing
between beta-strands far removed from this constrain is greatly perturbed.

Esposito G, Michelutti R, Verdone G, Viglino P, Hernandez H, Robinson CV, Amoresano A,
Dal Piaz F, Monti M, Pucci P, Mangione P, Stoppini M, Merlini G, Ferri G, Bellotti V.
Protein Sci 2000 9(5):831-45
Removal of the N-terminal hexapeptide from human beta2-microglobulin facilitates protein
aggregation and fibril formation.

Removal of the N-terminal hexapeptide from human beta2-microglobulin facilitates protein aggregation and fibril formation.

beta2-microglobulin with the first 3 residues

DN3 beta2-microglobulin (R3A mutant and with the first 3 residues)

DN3 beta2-microglobulin (H31Y mutant and with the first 3 residues)