N-Homocysteinyl-Proteins - Homocysteine in Protein Structure/Function and Human Disease - page 86

Fig. 5.13 Atomic force microscopy images of 30-day-old albumin samples. Control albumin (a),
N-Hcy-albumin (b), N-Hcy-albumin diluted 50-fold with bidistilled water (c), zoom of (c)onan
annular shape of protein aggregates (d). Image size of (a)-(c)is2 m; the scale bar

represents 50 nm. Color scale range of (a) 9 nm, (b) 40 nm, and (c) 9.7 nm. Image size of (d),
185 nm

μ m 2 μ

185 nm. The scale bar represents 40 nm. Line profile (e) of the annular aggregate
shown in (d); the height of the protein aggregate is about 2 nm, and the diameter of the annular
aggregate is 54 nm (Reproduced from [171])

act as a seed, stimulating the conversion of native albumin to molecular forms with
greater propensity to aggregate [171].
Atomic force microscopy and transmission electron microscopy analyses show
that aggregated N-Hcy-albumin undergoes time-dependent structural reorganiza-
tion. After 7 days, N-Hcy-albumin aggregates show no specific morphology and the
absence of well-ordered structures [171]. However, after longer time (30 days) the
aggregates show the presence of curly protofibrils and circular structures similar to
amyloid pores (Fig. 5.13 ).
Importantly, the levels of protein N-homocysteinylation that induce aggregation
and toxicity are close to those observed in albumin from patients with hyperhomo-
cysteinemia due to CBS deficiency [338]. Taken together, these findings identify a
mechanism that may explain the role of Hcy in neurological abnormalities observed
in CBS- [46] or MTHFR-deficient patients [339], as well as in cognitive impairment
and Alzheimer's disease in the general population [56].