Keratin IFs

Types I and II are the keratins that are found in various combinations in epithelial cells throughout the body. Keratin IFs must include representative subunits of both type I and type II IF subunits with each tissue having a characteristic combination. In contrast, type III IF subunits typically form homopolymers. They include IFs that are characteristic of less differentiated cells like glial or neuronal precursors, as well as those seen in more specialized cell types like smooth muscle cells and mature astrocytes. These three types of IF not only share sequence homology within their rod domains but their genes... 

The head and tail domains in keratin molecules generally contain a multitude of sites that allow keratin IFs to form covalent bonds with other proteins. For example, in the case of the keratin IFs in the inner root sheath, lysine to glutamine crosslinks have been characterized between the head and (more often) the tail domains in (generally) both Type I and Type II chains, envoplakin, epiplakin, the SPR2 (small proline-rich) family, and trichohyalin (Steinert et al., 2003). Likewise, in noninner root... 

Parry, D. A. D. (1995). Hard u-keratin IF A structural model lacking a head-lo-lail molecular overlap but having hybrid features characteristic of both epidermal keratin and vimentin IF. Proteins 22, 267-272. 

Parry, D. A. D. (1997). Protein chains in hair and epidermal keratin IF Structural features and spatial arrangements. In Formation and Structure of Human Hair (P. Jolles, H. Zahn, and H. Hocker, Eds.), pp. 177-207. Birkhauser, Basel. 

Keratin IFs exhibit different motile behaviors compared with type III and IV IFs, and continue to move in the absence of MT in cells treated with MT inhibitors, such as nocodazole. It has been proposed that actin may be involved in their transport (Yoon et al., 2001). Time lapse imaging of keratin-GFP has revealed that keratin IF formation begins in the cell cortex in a region enriched in actin and required for both intact MT and actin, and that actin governs the organization and movement of keratin in Xenopus egg extracts (Weber and Bement, 2002). Less is known about specific mediators of these interactions, although the fact that myosin Va associates with NFs raises the interesting possibility that other such interactions may exist for keratins. 

To compare the backbone mobility of the rod domain with the end domains, keratin IF was labeled with L-[l- C]leucine, as more than 90% of the... 

In modem usage, the observed filaments in fiber sections are strictly called hard keratin IFs. Traditionally, these IFs— known as microfibrils—have probably received more intensive study over the years than other fiber stmctural components. The range of the various... 

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