K88 major fimbrial subunit. Fimbriae (also called pili), are polar filaments radiating from the surface of the bacterium to a length of 0.5-1.5 micrometers and numbering 100-300 per cell. They enable bacteria to colonize the epithelium of specific host organs. K88 fimbria, 0.1-1 micrometer in length and 7 nanometers in diameter, is composed of about 100 identical subunits. The protein exists in several antigenic variants. Belongs to the fimbrial K88 protein family.