Site-specific mutagenesis of the human interleukin-1 beta gene: structure-function analysis of the cysteine residues.

Human interleukin-1 beta (IL-1 beta) has two cysteines located at amino acid residues 8 and 71 of the mature protein consisting 153 amino acids. To clarify the role of these characteristic cysteine residues in IL-1 beta, at first, an expression plasmid for site-specific mutagenesis has been constructed by inserting the ori and intergenic region of phage f1 into the IL-1 beta expression vector. The plasmid can be used not only for isolation of the modified IL-1 beta gene but for expression of the mutant protein in Escherichia coli. Using this plasmid, each of the cysteine codons in IL-1 beta gene was changed to serine or alanine codon, or deleted. The modified IL-1 beta showed that the two cysteine residues in IL-1 beta are not essential for biological activity but not to be eliminated for the maintenance of the functional structure of IL-1 beta.