THE ASSEMBLY OF KERATINS FROM HIGHER-PLANT CELLS

In vitro assembly and morphological characteristics of purified 58 kDa, 52 kDa, 50 kDa, and 45 kDa polypeptides in the leaves and the cotyledons of the cabbage (Brassica pekinensis Rupt.) were investigated by electron microscopy and scanning tunneling microscopy. The three or four purified intermediate filament (IF) polypeptides can spontaneously assemble into intermediate filaments in vitro with a 23-24 nm axial repeat, which indicates that keratin Ifs in higher plant cells have the same molecular arrangement as in animal cells. STM images suggest that the plant keratin filaments display a pronounced structural polymorphism, which can be composed of 3 nm, 4.5 nm, or 6 nm wide keratin protofilaments.