N-Homocysteinyl-Proteins - Homocysteine in Protein Structure/Function and Human Disease - page 90

and aggregation rates depend on the extent of N-homocysteinylation and tempera-
ture. The DLS and microscopic studies reveal the formation of large aggregates of
N-Hcy-caseins (1-3 μ m). N-Homocysteinylation of α (S1)- and β -caseins results in

the formation of regular spheres, whereas N-homocysteinylated -casein forms thin

unbranched fibrils about 400-800 nm long. Amyloid character of N-Hcy-

κ

-casein
fibrils is further confirmed by the changes in Congo red spectra. These data indicate
that N-homocysteinylation of intrinsically unstructured proteins restricts their
structure to the

κ

-sheet conformation, which facilitates amyloidal transformation
of native caseins structures [354].

β

5.4.5.7 N -Hcy-Crystallin

Preponderance of evidence indicates that hyperhomocysteinemia is often
associated with various diseases of the eye. For example, in humans one of the
manifestations of severe hyperhomocysteinemia due to CBS deficiency is the
dislocated optic lens, ectopia lentis [46]. However, the molecular basis of pathology
of the visual system induced by elevated Hcy is not known. Lens protein
modifications are often underlying problems, becoming more prevalent with age.
Thus, it is likely that lens protein modification by N-homocysteinylation might
contribute to pathological consequences of hyperhomocysteinemia affecting the
eye. Indeed, bovine -crystallin, a major component of lens protein pool, is known

to be susceptible to N-homocysteinylation in vitro (Table 3.3 ) [78] and to carry a
small amount of N-linked Hcy in vivo (Table 5.4 ) [297]. The molecular
consequences of bovine lens protein N-homocysteinylation have been examined
in a recent study using spectroscopic techniques, SDS-PAGE, and Western blot
analysis [355]. Similar to other proteins [78], N-homocysteinylation induces lens
protein aggregation, which, if it were to occur in the eye, would cause vision
problems. Lens protein aggregates undergo fibrillation, which is detected by
increases in Congo red absorption and thioflavin T fluorescence. SDS-PAGE and
Western blotting of N-homocysteinylated lens proteins show that essentially all
detectable eye lens crystallins become prone to aggregation after the modification,
with N-Hcy-

α

-crystallin comprising the major portion of lens protein aggregate.
These findings suggest that lens protein N-homocysteinylation is a possible mecha-
nism accounting for the association of hyperhomocysteinemia with impairments of
the visual system [355].

α

5.4.5.8 N -Hcy-Dynein

Folate deficiency markedly affects hippocampal cell proliferation, migration,
differentiation, survival, vesicular transport, and synaptic plasticity [299]. This
occurs through alterations in signaling, impaired expression of proteins involved
in elongation and stabilization of axons and dendrites, defect in cell polarity and