Intermediate filament associated proteins IFAP

The cytoskeleton also contains different accessory proteins, which, in accordance with their affinities and functions, are designated as microtubule-associated proteins (MAPs), actin-binding proteins (ABPs), intermediate-filament-associated proteins (IFAPs), and myosin-binding proteins. This chapter is focused on those parts of the cytoskeleton that are composed of microfilaments and microtubules and their associated proteins. The subject of intermediate filaments is dealt with in detail in Volume 2. 

Intermediate filament associated proteins (IFAPs) coordinate interactions between intermediate filaments (IFs) and other cytoskeletal elements and organelles, including membrane-associated junctions such as desmosomes and hemidesmosomes in epithelial cells, costameres in striated muscle, and intercalated discs in cardiac muscle. IFAPs thus serve as critical connecting links in the IF scaffolding that organizes the cytoplasm and confers mechanical stability to cells and tissues. However, in recent years it has become apparent that IFAPs are not limited to structural... 

KAP, keratin-associated proteins (formerly IFAP intermediate filament-associated proteins)... 

Morphologically, the fibres are composed of the cortex and the cuticle. Each of the two components is formed of various other morphological components (Table 9.6.3). The cortex contains cortical cells and the cell membrane complex. The cortical cell is further composed of macro-fibrils and intermacro-fibrillar material. The macro-fibrils consist of micro-fibrils and intermicro-fibrillar matrix. In summary, the cortex is formed of micro-fibrils (intermediate filament, IF, or keratin proteins, KP) and keratin associated proteins (IFAP or KAP), which compose the intermicrofibrillar matrix containing cytoplasmatic and nuclear remnants. This ensemble is wrapped up in the cuticle, as an external sheath which also has its own architecture, being formed of four layers the epicuticle, the a-layer, the exocuticle and the endocuticle. 

One family of IFAPs, the plakins, is responsible for linking IFs with both microtubules and mlcrofllaments. One plakln family member is plectin, a 500,000-MW protein that has been shown to cross-link intermediate filaments with microtubules and actln filaments in vitro. Plectin also Interacts with other cytoskeletal proteins, including spectrin, microtubule-associated proteins, and lamin B. Immunoelectron microscopy reveals gold-labeled antibodies to plectin decorating short, thin connections between microtubules and vimentin. 

As matrix or interfilamentous proteins, the high-sulfur proteins and the high-tyrosine proteins (see below) are now often referred to as interfilamentous associated proteins or IFAPs, especially when they are considered in the context of intermediate filament systems and terminology [124,192,229,233],... 

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