Role of Isoleucine in protein structure. - (Sep/18/2012 )

What is the role of isoleucine in protein structure?. I found that many recombinant proteins have substituted threonine by isoleucine. I don't know the goal of this substitution.

The only reason I see it would be that Ile is bulkier and more hydrophobic vs Thr which is smaller and has a hydroxyl that can make hydrogen bonds so Ile would block pockets/make pocket smaller and would disrupt hydrogen bond formation...but these are speculations based on the structural knowledge. I do not have exact explanation why Thr-->Ile. Except that on the codon level you change a C in a T and you get easily from Thr to Ile and these C-->T transitions are very easy to happen.