Together with KRT19, helps to link the contractile apparatus to dystrophin at the costameres of striated muscle. Heterotetramer of two type I and two type II keratins (By similarity). Forms a heterodimer with KRT18 (By similarity). Associates with KRT20 (By similarity). Interacts with PNN (By similarity). When associated with KRT19, interacts with DMD (By similarity). Interacts with APEX1 (By similarity). Interacts with GPER1 (By similarity). Interacts with EPPK1 (By similarity). O-glycosylated. O-GlcNAcylation at multiple sites increases solubility, and decreases stability by inducing proteasomal degradation (By similarity). O-glycosylated (O-GlcNAcylated), in a cell cycle-dependent manner. There are two types of cytoskeletal and microfibrillar keratin: I (acidic; 40-55 kDa) and II (neutral to basic; 56-70 kDa). Belongs to the intermediate filament family.