Oligomeric
states of the amyloid β-protein (Aβ) appear to be causally
related to Alzheimer’s disease (AD). Recently, two familial
mutations in the amyloid precursor protein gene have been described,
both resulting in amino acid substitutions at Ala2 (A2) within Aβ.
An A2V mutation causes autosomal recessive early onset AD. Interestingly,
heterozygotes enjoy some protection against development of the disease.
An A2T substitution protects against AD and age-related cognitive
decline in non-AD patients. Here, we use ion mobility-mass spectrometry
(IM-MS) to examine the effects of these mutations on Aβ assembly.
These studies reveal different assembly pathways for early oligomer
formation for each peptide. A2T Aβ42 formed dimers, tetramers,
and hexamers, but dodecamer formation was inhibited. In contrast,
no significant effects on Aβ40 assembly were observed. A2V Aβ42
also formed dimers, tetramers, and hexamers, but it did not form dodecamers.
However, A2V Aβ42 formed trimers, unlike A2T or wild-type (wt)
Aβ42. In addition, the A2V substitution caused Aβ40 to
oligomerize similar to that of wt Aβ42, as evidenced by the
formation of dimers, tetramers, hexamers, and dodecamers. In contrast,
wt Aβ40 formed only dimers and tetramers. These results provide
a basis for understanding how these two mutations lead to, or protect
against, AD. They also suggest that the Aβ N-terminus, in addition
to the oft discussed central hydrophobic cluster and C-terminus, can
play a key role in controlling disease susceptibility