Structure, stability and biological properties of a N-terminally truncated form of recombinant human interleukin-6 containing a single disulfide bond.
A mutant species of the 185-residue chain of human interleukin-6 lacking 22-residues at its N-terminus and with a Cys-->Ser substitution at positions 45 and 51 was produced in Escherichia coli. The 163-residue protein des-(A1-S22)-[C45S, C51S]interleukin-6, containing a single disulfide bridge, formed inclusion bodies. Mutant interleukin-6 was solubilized in 6 M guanidine hydrochloride, subjected to oxidative refolding and purified to homogeneity by ammonium sulfate precipitation and hydrophobic chromatography. The purity of the mutant species was established by electrophoresis, isoelectrofocusing and reverse-phase HPLC and its structural identity was checked by N-terminal sequencing of both the intact protein and several of its proteolytic fragments. Electrospray mass spectrometry analysis of mutant interleukin-6 gave a molecular mass of 18,695 +/- 2 Da in excellent agreement with the calculated value. Circular dichroic, fluorescence emission and second-derivative ultraviolet absorption spectra indicated that mutant interleukin-6 maintains the overall secondary and tertiary structure, as well as stability characteristics, of the recombinant wild-type human interleukin-6. The urea-induced unfolding of mutant interleukin-6, monitored by circular dichroic measurements in the far-ultraviolet region, occurs as a highly cooperative process with a midpoint of denaturation at 5.5 M urea. The data of the reversible unfolding of mutant interleukin-6 mediated by urea were used to calculate a value of 20.9 +/- 0.4 kJ.mol-1 for the thermodynamic stability of the protein at 25 degrees C in the absence of denaturant. The biological activity of mutant interleukin-6 was evaluated in vitro by the hybridoma proliferation assay, and in vivo by measuring thrombopoiesis in monkeys. Dose/response effects of the mutant were comparable or even higher than those of the wild-type protein. Overall the results of this study show that mutant interleukin-6 is a biologically active cytokine, which could find practical use as a therapeutic agent.
Breton
J
J
Pharmacia-Farmitalia, Bioscience Centre, Nerviano, Milan, Italy.
La Fiura
A
A
Bertolero
F
F
Orsini
G
G
Valsasina
B
B
Ziliotto
R
R
De Filippis
V
V
Polverino de Laureto
P
P
Fontana
A
A
D000595:Amino Acid Sequence; D000818:Animals; D002455:Cell Division; D002460:Cell Line; D004220:Disulfides / Q000737:chemistry*; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D015850:Interleukin-6 / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism
D004220:Disulfides; D015850:Interleukin-6; D011994:Recombinant Proteins