Evidence for the importance of a positive charge and an alpha-helical structure of the C-terminus for biological activity of human IL-6.

Thirteen point mutations of human interleukin-6 at the C-terminus were constructed at the cDNA-level. Two degenerate oligonucleotide primers were used for PCR synthesis of two groups of point mutations at positions 182 and 184. The mutated cDNAs were in vitro transcribed and translated and subsequently assayed for biological activity in the B9 cell proliferation test. Our results confirm our former findings obtained with deletion mutants on the importance of the C-terminus of IL-6 for biological activity. In addition, we now present evidence for the importance of an alpha-helix at the C-terminus of IL-6 and the presence of the positive charge at position 182 for biological activity.