Molecular model of an alternative splice variant of human IL-4, IL- 4δ2, a naturally occurring inhibitor of IL-4-stimulated T cell proliferation

The molecular model of IL-4δ2, a naturally occurring splice variant of human IL-4 with exons 1, 3, and 4 in an open reading frame, is described. The second exon codes the main part of the long loop AB connected the helices A and B in parallel superposition. Therefore the hydrophobic core and the native fold of the rest part of IL-4δ2 molecule could be preserved without any significant changes only in the case of revolution of the helix A relative to other helices. In the result, the dominated a left-handed four- helix bundle structure of IL-4 with an up-up-down-down structural pattern is transformed to the IL-4δ2 structure with a down-up-down-down structural pattern.