Keratin-associated proteins (KAPs) are cysteine-rich proteins synthesized during the differentiation of hair matrix cells, and form hairfibres in association with hair keratin intermediate filaments [, ]. This entry also includes the high-sulfur and high-tyrosine keratins from sheep and goats.In the hair cortex, hair keratin intermediate filaments are embedded in an interfilamentous matrix, consisting of hair keratin-associated proteins, which are essential for the formation of a rigid and resistant hair shaft through their extensive disulfide bond cross-linking with abundant cysteine residues of hair keratins []. The matrix proteins include the high-sulfur and high-glycine-tyrosine keratins.
The KAP (after Kidins220/ARMS and PifA) family of predicted NTPases are sporadically distributed across a wide phylogenetic range in bacteria and in animals. Many of the prokaryotic KAP NTPases are encoded in plasmids and tend to undergo disruption to form pseudogenes. A unique feature of all eukaryotic and certain bacterial KAP NTPases is the presence of two or four transmembrane helices inserted into the P-loop NTPase domain. These transmembrane helices anchor KAP NTPases in the membrane such that the P-loop domain is located on the intracellular side [].
The keratin-associated proteins (KAPs) are fundamental components of hair and wool fibres []. This entry represents KRTAP8-1, which is a high sulphur (HS) KAP [].
Membrane-spanning 4-domains subfamily A member 3 (MS4A3), also known as HTm4, is an hematopoietic modulator for the G1-S cell cycle transition []. HTm4 binds to the Cdk-associated Phosphatase (KAP)-Cdk2-Cyclin A complex, triggering the dissociation of cyclin A and facilitating dephosphorylation of Cdk2 by KAP [, ].
