Do proteins generally contain phosphorus and sulfur? I've heard that proteins generally contain six main elements - carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. I know that proteins are made from amino acids. Amino acids are composed of an amino group, a carboxyl group, a lone hydrogen atom, and a side chain that varies between amino acids. Of the 20 major amino acids, none of them have a side chain that contains phosphorus. Only cysteine and methionine contain sulfur. So, are sulfur and phosphorus atoms really characteristic in the structure of a protein?

Of the 22 known proteinogenic amino acids, all contain hydrogen, carbon, nitrogen and oxygen. Some (methionine and cysteine) contain sulfur while one (selenocysteine) contains selenium. None contain phosphorus, but this element can be incorporated by:

1. Post translational phosphorylation of various residues. This often allows/prevents binding of other proteins and/or triggers a conformational change in the target protein. It is also necessary for proper folding of some proteins (example). Sulfur can also be incorporated in a similar manner (sulfation).

2. Incorporation of phosphorus containing prosthetic groups). This can occur covalently and is necessary for the function of some proteins. Sulfur can also be incorporated as part of prosthetic groups.




You may also consider the other elements necessary for the structure/function of many proteins: iodine in thyroglobulin, iron in hemoglobin, etc...