Carbohydrate recognition site of interleukin-2 in relation to cell proliferation.

Interleukin-2 (IL-2) is a cytokine with important roles in the immune system. IL-2 initially binds a high mannose-type glycan and a specific peptide sequence of the IL-2 receptor alpha-subunit and sequentially forms a high affinity complex of IL-2.IL-2 receptor alpha-, beta-, and gamma-subunits. This formation induces cellular signaling and cell proliferation (Fukushima, K., and Yamashita, K. (2001) J. Biol. Chem. 276, 7351-7356). To determine the carbohydrate-binding site of IL-2, we prepared wild-type and point-mutated (35)S-IL-2 by an in vitro transcription and translation method. We found that wild-type (35)S-IL-2 tends to form a dimer spontaneously, and the dimeric form has both carbohydrate recognition activity and cell proliferation activity. Moreover, substitution of Asn-26 in IL-2 with Gln or Asp conserved the dimeric form and affected the carbohydrate recognition activities in correspondence with the cell proliferation activities, suggesting that Asn-26 in IL-2 is involved in the carbohydrate recognition site. These results suggest that the carbohydrate recognition of IL-2 dimer triggers formation of high affinity complex (IL-2.IL-2Ralpha, -beta, -gamma)(2), and the hetero-octamer stimulates IL-2-dependent T-cell proliferation by intensifying cellular signaling.