Like its name suggests, a protein fiber is a fiber that is made of protein or animal based, wool and silk.
wool is a protein fiber from sheep. it's easily dyed so staining can be a problem. also colour can be removed with strong alkaline and oxidizing bleaches. wool also degrades with long and repeated exposure to high alkalinity, it will completely dissolve in a mix of 6% soloution of chlorine bleach. always leave wool carpets in a neutral state by rinsing with acid solution of a pH 5.5 to 6.5
Silk is mostly found in rugs. when encountered it should be treated with the same precautions as wool, only wit more delicacy. i.e avoid bleach and take care with alkaline solutions and aggressive tamping action. exercise extreme caution when using volatile dry solvents ( alcohol perchloroethylene, trichlorethylene) it can cause colour migration.