What are the types of protein sulfation and their implications in protein-protein interactions?

Protein sulfation is a post-translational modification, where a sulfate group gets added to a specific amino acid residue in a protein. This modification adds a negative charge to the protein which can affect its structure or function. There are primarily two types of protein sulfation - tyrosine sulfation and N-terminal methionine sulfation.

Tyrosine Sulfation: This type of sulfation involves the addition of sulfate groups to the hydroxyl group of a tyrosine residue in a protein. The enzyme Tyrosylprotein sulfotransferase (TPST) is responsible for performing tyrosine sulfation. Proteins that are targeted for tyrosine sulfation often play crucial roles in protein-protein interactions. They are involved in various biological processes like blood clotting, inflammation, and viral entry into host cells. Defects in tyrosine sulfation can lead to diseases like atherosclerosis, arthritis, and various infectious diseases.

N-Terminal Methionine Sulfation: This type of sulfation is less common, and it involves the addition of sulfate groups to the N-terminal methionine residues of a protein. The enzyme involved in this type of sulfation is yet to be clearly identified. The functional implications of this sulfation type are not as well-studied as tyrosine sulfation, but it is considered to play a role in protein stability and lifespan.

Protein sulfation can influence protein-protein interactions in several ways. Addition of a sulfate group can lead to changes in protein shape or charge distribution, thus altering how proteins interact with one another. This can affect the strength or specificity of protein interactions. Furthermore, some proteins may require sulfation to be recognized and interact with other proteins. For example, sulfated tyrosine residues have been found to be crucial for the binding of chemokine receptors with their ligands, and for the binding of coagulation factors with their substrates. Therefore, alterations in protein sulfation can have striking effects on the biological processes mediated by these proteins.