The diphtheria toxin transmembrane domain as a pH sensitive membrane anchor for human interleukin-2 and murine interleukin-3

We have constructed two fusion proteins T-hIL-2 and T-mIL-3 in which human interleukin-2 (hIL-2) or murine interleukin-3 (mIL-3) are fused to the C-te rminus of the diphtheria toxin transmembrane domain (T domain). Two additio nal fusion proteins, T-(Gly(4)-Ser)(2)-hIL-2 and T-(Gly(4)-Ser)(2)-mIL-3, w ere derived by introduction of the (Gly(4)-Ser)(2) spacer between the T dom ain and cytokine components. Recognition of the hIL-2 receptor or the mIL-3 receptor by the corresponding recombinant proteins was demonstrated by the ir capacity to stimulate cytokine-dependent cell lines. All proteins retain ed the capacity of the T domain to insert into phospholipid membranes at ac idic pH, Finally, anchoring of both cytokines to the membrane of lipid vesi cles or living cells was assessed by specific antibody recognition. Our res ults show that the T domain fused to the N-terminus of a given protein can function as a pH sensitive membrane anchor for that protein.