Wool microfibrillar keratin. There are two types of cytoskeletal and microfibrillar keratin: I (acidic; 40-55 kDa) and II (neutral to basic; 56-70 kDa). The low-sulfur proteins, derived from the microfibrillar fraction of wool extracts, are composed of two families, each consisting of 4 homologous subunits: the type I components (8C-1, 8C-2, 8A and 8B) and the type II components (5, 7A, 7B, and 7C). Belongs to the intermediate filament family.