Disulfide and secondary structures of recombinant human granulocyte colony stimulating factor

Molecular characteristics and secondary structures of recombinant methionyl human granulocyte colony stimulating factor produced by genetically engineered Escherichia coli are described. Limited radiolabeling of the protein with tritiated iodoacetate and determination of the labeled residue revealed that this recombinant protein contains only one free cysteine at position 17 which is not essential for activity. The free cysteine is inaccessible to modification unless the molecule is unfolded under denaturing conditions. The molecule forms two disulfide bridges which were assigned as Cys(36)-Cys(42) and Cys(64)-Cys(74) based on the results of isolation and characterization of disulfide-containing peptides obtained from a subtilisin digest of the intact protein. CD analyses and secondary structure prediction suggest that the molecule is abundant in alpha-helical structures.