Structural evaluation of evolutionary differences between human current and ancestral IL2 protein

Objectives: Interleukin-2 (IL-2) is a well-known monomeric T-cell growth factor which is produced primarily by activated CD4+ T cells following exposure to antigen. We have found Thr 103 deletion in highly conserved IL2 protein in some primates involving human by multiple alignment of full length protein sequence using Mega 6. Interaction of IL2 with its receptors is critical for its biological function. Therefore, we decided to compare human and ancestral IL2 structure of IL2 before occurrence of deletion for predicting their differential evolutionary function using modeling and molecular dynamics simulation. At first, model of human IL2 and ancestral IL2 were made according to two templates (PDB codes: 1M47 and 3INK) using modeler 10. Then the best obtained models were used as starting structures for 20 ns MD simulation via Gromacs 5 package. Our results showed that deletion of Thr 103 in current IL2 lead to compactness and decrease of flexibility of current IL2 relative to ancestral IL2 and probably increase in its stability.