No abstract

Interleukin 13 (IL‐13), a member of the α‐helical family of cytokines, has ∼30% primary sequence homology with IL‐4 and shares a common receptor component. The biologically active rhIL‐13 is monomeric and non‐glycosylated, and contains two disulfide bonds as determined by comparative electrospray mass spectrometric (MS) analysis of the protein before and after reduction with dithiothreitol–dithioerythritol. A trypsin‐resistant core peptide of rhIL‐13 was isolated and analyzed by plasma desorption (PD) MS, identifying a disulfide‐linked core peptide. Subsequent digestion of this core peptide by pepsin, followed by PDMS analysis of the resulting cystine‐containing peptic fragments, provided rapid determination of the existing disulfide bonds between cysteine residues 28–56 and 44–70. This disulfide arrangement is similar to that observed for the analogous four internal cysteine residues in hIL‐4. The conservation of disulfide bond arrangements between hIL‐13 and hIL‐4, coupled with their α‐helical structure and sequence homologies, confirms that IL‐13 and IL‐4 are structural homologues. It is also consistent with their reported similarities in biological function and receptor binding kinetics. Copyright © 2000 John Wiley & Sons, Ltd.

Interleukin 13 (IL-13), a member of the a-helical family of cytokines, has ∼30% primary sequence homology with IL-4 and shares a common receptor component. The biologically active rhIL-13 is monomeric and nonglycosylated, and contains two disulfide bonds as determined by comparative electrospray mass spectrometric (MS) analysis of the protein before and after reduction with dithiothreitol-dithioerythritol. A trypsin-resistant core peptide of rhIL-13 was isolated and analyzed by plasma desorption (PD) MS, identifying a disulfidelinked core peptide. Subsequent digestion of this core peptide by pepsin, followed by PDMS analysis of the resulting cystine-containing peptic fragments, provided rapid determination of the existing disulfide bonds between cysteine residues 28-56 and 44-70. This disulfide arrangement is similar to that observed for the analogous four internal cysteine residues in hIL-4. The conservation of disulfide bond arrangements between hIL-13 and hIL-4, coupled with their a-helical structure and sequence homologies, confirms that IL-13 and IL-4 are structural homologues. It is also consistent with their reported similarities in biological function and receptor binding kinetics.