383
structural optimization for attaining maximum coloration, apparently resulting from
natural evolution. Upon increasing the material refractive index above the level provided by nature, there is an interesting transition from a photonic pseudogap to a
complete bandgap,” (Yin et al. 2012 ).
The results discussed above additionally support the hypothesis that air nanostructures in feather barbs and colour-producing protein can be self-assembled. This
is done by “arrested phase separation of polymerizing β-keratin from the cytoplasm
of medullary cells. Such avian amorphous photonic nanostructures with isotropic
optical properties may provide biomimetic inspiration for photonic technology”
(Saranathan et al. 2012 ).
11.1 Intermediate Filaments
Epithelial cells are, probably, the place for location of keratins as one of the largest
subgroup of intermediate fi lament (IF) proteins. IF of keratinous origin undergo
complex regulation involving post-translational modifi cations and interactions with
self and with various classes of associated proteins ( Coulombe and Omary 2002 ).
It was suggested that “the keratin-fi lament cycle of assembly and disassembly is a
major mechanism of intermediate-fi lament network plasticity, allowing rapid adaptation to specifi c requirements, notably in migrating cells,” (Kölsch et al. 2010 ).
Intermediate fi laments (IFs), microfi laments (MFs) and microtubules (MTs)
represent three main kinds of cytoskeletal fi laments in eukaryotic cells (see for
review Karantza 2011 ). Previously, IFs have been considered as “mechanical integrators of cellular space” (Lazarides 1980 ). Today, they are known to impart
mechanical stability to cells and tissues (Kreplak and Fudge 2007 ). From structural
view, there are some differences between IFs, MFs and MTs. For example,
– “MFs are composed of 6-nm intertwined actin chains and are responsible for
resisting tension and maintaining cellular shape, forming cytoplasmic protuberances and participating in cell-cell and cell-matrix interactions;
– the IFs 10 nm in diameter are more stable than actin fi laments, organize the internal three-dimensional cellular structure. Similarly to MFs, they also function in
cell shape maintenance by bearing tension,” (Karantza 2011 ; see also Herrmann
et al. 2009 ; Pollard and Cooper 2009 );
– “IFs are non-polar, and they do not exhibit large globular do mains. IF molecules
associate via a coiled-coil interaction into dimers and higher oligomers;
– all IFs have a dimeric central rod domain, which is a coiled coil of two parallel
α-helices fl anked by head and tail domains of variable lengths. They are among
the most chemically stable cellular structures, resisting high temperature, high
salt and detergent solubilization;
– antiparallel molecular dimers (referred to as tetramers) polymerize in a staggered
manner to make apolar protofi laments (3 nm in diameter). These in turn associate
to protofi brils (4–5 nm in diameter), and then form the 10-nm Ifs;
11.1 Intermediate Filaments
structural optimization for attaining maximum coloration, apparently resulting from
natural evolution. Upon increasing the material refractive index above the level provided by nature, there is an interesting transition from a photonic pseudogap to a
complete bandgap,” (Yin et al. 2012 ).
The results discussed above additionally support the hypothesis that air nanostructures in feather barbs and colour-producing protein can be self-assembled. This
is done by “arrested phase separation of polymerizing β-keratin from the cytoplasm
of medullary cells. Such avian amorphous photonic nanostructures with isotropic
optical properties may provide biomimetic inspiration for photonic technology”
(Saranathan et al. 2012 ).
11.1 Intermediate Filaments
Epithelial cells are, probably, the place for location of keratins as one of the largest
subgroup of intermediate fi lament (IF) proteins. IF of keratinous origin undergo
complex regulation involving post-translational modifi cations and interactions with
self and with various classes of associated proteins ( Coulombe and Omary 2002 ).
It was suggested that “the keratin-fi lament cycle of assembly and disassembly is a
major mechanism of intermediate-fi lament network plasticity, allowing rapid adaptation to specifi c requirements, notably in migrating cells,” (Kölsch et al. 2010 ).
Intermediate fi laments (IFs), microfi laments (MFs) and microtubules (MTs)
represent three main kinds of cytoskeletal fi laments in eukaryotic cells (see for
review Karantza 2011 ). Previously, IFs have been considered as “mechanical integrators of cellular space” (Lazarides 1980 ). Today, they are known to impart
mechanical stability to cells and tissues (Kreplak and Fudge 2007 ). From structural
view, there are some differences between IFs, MFs and MTs. For example,
– “MFs are composed of 6-nm intertwined actin chains and are responsible for
resisting tension and maintaining cellular shape, forming cytoplasmic protuberances and participating in cell-cell and cell-matrix interactions;
– the IFs 10 nm in diameter are more stable than actin fi laments, organize the internal three-dimensional cellular structure. Similarly to MFs, they also function in
cell shape maintenance by bearing tension,” (Karantza 2011 ; see also Herrmann
et al. 2009 ; Pollard and Cooper 2009 );
– “IFs are non-polar, and they do not exhibit large globular do mains. IF molecules
associate via a coiled-coil interaction into dimers and higher oligomers;
– all IFs have a dimeric central rod domain, which is a coiled coil of two parallel
α-helices fl anked by head and tail domains of variable lengths. They are among
the most chemically stable cellular structures, resisting high temperature, high
salt and detergent solubilization;
– antiparallel molecular dimers (referred to as tetramers) polymerize in a staggered
manner to make apolar protofi laments (3 nm in diameter). These in turn associate
to protofi brils (4–5 nm in diameter), and then form the 10-nm Ifs;
11.1 Intermediate Filaments