This green structure, the IRS itself is phosphorylated at four tyrosine residues. So upon binding, the IRS itself is phosphorylated by the insulin receptor kinase. Now, what is the point of asphorylating this region? And in general, what exactly is the function of the IRS one structure? Well, the IRS protein is not actually a protein that activates something in the pathway. Instead, what it does is it functions as an adaptive protein.