166
M. Pecul and W. Dzwolak
area on the Ramachandran plot assigned to β-sheets. This structural polymorphism
of extended structures, especially those aggregated in the form of so-called amyloid
fibrils, may lead to pronounced differences in corresponding far-uv Cd spectra
[55, 56]. On the other hand, the CD signal of a typical β-sheet structure found in
globular proteins yields a rather simple spectrum containing a positive band at ca.
195 nm (ππ*) and a negative one at 216 nm (nπ*), as shown in Fig. 6.2.
the polyproline II conformation is thought to represent a major share of unfolded
or disordered protein state. It is also assumed by charged homopolypeptide chains
such as poly-L-lysine and poly-L-glutamic acid at neutral ph. the corresponding
Cd spectra are rather flat with a stronger negative band at 200 nm and a very weak
positive one near 218 nm. Typically, a gradual denaturation of α-helical protein e.g.
by temperature will be followed in far-uv Cd spectra by a stepwise decay of the
208 nm/222 nm negative bands and a simultaneous appearance of the spectral features of the emerging polyproline II conformation. Certainly, denaturation or even
covalent degradation of a protein does not have to result in a complete breakdown
of the native structure. Still, far-uv Cd spectroscopy has proven sensitive to follow
such limited or localized changes in the native state, as has been recently shown in
a time-lapse spectroscopic study on enzymatically-degraded β-lactoglobulin and
β-casein [57].
Finally, the variety of turns present in protein molecules will also contribute
to the net far-uv Cd spectrum. Because soluble polypeptide model with a neat
turn structure of a particular type are often scarce or inaccessible, assignment of
Fig. 6.2 Far uv Cd spectra
associated with various types
of secondary structure. Solid
line, α- helix; long dashed
line, anti-parallel (β-sheet;
dotted line, type I (β-turn;
cross dashed line, extended
31-helix or poly (Pro) II
helix; short dashed line, irregular structure, according to
Kelly, Jess and Price [18]
M. Pecul and W. Dzwolak
area on the Ramachandran plot assigned to β-sheets. This structural polymorphism
of extended structures, especially those aggregated in the form of so-called amyloid
fibrils, may lead to pronounced differences in corresponding far-uv Cd spectra
[55, 56]. On the other hand, the CD signal of a typical β-sheet structure found in
globular proteins yields a rather simple spectrum containing a positive band at ca.
195 nm (ππ*) and a negative one at 216 nm (nπ*), as shown in Fig. 6.2.
the polyproline II conformation is thought to represent a major share of unfolded
or disordered protein state. It is also assumed by charged homopolypeptide chains
such as poly-L-lysine and poly-L-glutamic acid at neutral ph. the corresponding
Cd spectra are rather flat with a stronger negative band at 200 nm and a very weak
positive one near 218 nm. Typically, a gradual denaturation of α-helical protein e.g.
by temperature will be followed in far-uv Cd spectra by a stepwise decay of the
208 nm/222 nm negative bands and a simultaneous appearance of the spectral features of the emerging polyproline II conformation. Certainly, denaturation or even
covalent degradation of a protein does not have to result in a complete breakdown
of the native structure. Still, far-uv Cd spectroscopy has proven sensitive to follow
such limited or localized changes in the native state, as has been recently shown in
a time-lapse spectroscopic study on enzymatically-degraded β-lactoglobulin and
β-casein [57].
Finally, the variety of turns present in protein molecules will also contribute
to the net far-uv Cd spectrum. Because soluble polypeptide model with a neat
turn structure of a particular type are often scarce or inaccessible, assignment of
Fig. 6.2 Far uv Cd spectra
associated with various types
of secondary structure. Solid
line, α- helix; long dashed
line, anti-parallel (β-sheet;
dotted line, type I (β-turn;
cross dashed line, extended
31-helix or poly (Pro) II
helix; short dashed line, irregular structure, according to
Kelly, Jess and Price [18]