ANALYSIS OF 3 HUMAN INTERLEUKIN-5 STRUCTURES SUGGESTS A POSSIBLE RECEPTOR-BINDING MECHANISM

We compared three crystal structures of human interleukin 5 (hIL5) exp ressed in either E. coli (hIL5(E.coli)), Sf9 cells (hIL5(Sf9)) or Dros ophila cells (hIL5(Drosophila)). The dimeric hIL5 structures show subt le but significant conformational differences which are probably a con sequence of the different crystallization conditions trapping this pro tein into one of two states. We refer to these two distinct conformati ons as the 'open' and 'tight' state, according to the packing around t he cleft between the two subunits. We hypothesize that these two stabl e conformational states reflect the structure of the free or receptor bound hIL5. (C) 1998 Federation of European Biochemical Societies.