A chaperone protein is used in the cell to ensure proper protein folding, among other cellular functions.

Protein should not be capitalized unless it is at the start of a sentence or part of a proper noun or title. For example, "I ate chicken for dinner. It is a good source of protein."

My friend is protein deficient, and lacks the proper amount.

albumin

Proteins are very necessary for proper growth of your baby. So many times your doctor will prescribe you protein supplements.