CD AND FLUORESCENCE STUDIES OF THE HUMAN GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR AND RELATED PEPTIDE CONFORMATIONS IN AQUEOUS-SOLUTION

The absorption, CD, and fluorescence emission spectra, and the fluores cence emission and depolarization lifetimes of the human granulocyte-m acrophage colony-stimulating factor (hGM-CSF) and related peptides pre viously tested for their immunological activity, were measured in wate r at various pHs and temperatures to obtain information on their confo rmation in solution. The aim was to correlate the amino acid sequences , and the chain conformations and dynamics of the peptides, with their immunological properties. The CD spectrum of hGM-CSF revealed, as exp ected, a structure in solution similar to that in the crystalline stat e, but the fluorescence data suggest that the Trp 122 residue is more accessible to the solvent than the x-ray data would lead one to expect . They also suggest that some flexibility exists between the protein's two domains, one made up of the alpha-helices A and C and the other o f the alpha-helices B and D plus the two beta-strands. In aqueous solu tion, none of the tested peptide CD spectra could be linked to a recog nizable ordered conformation, i.e., an alpha-helix or a beta-sheet. Th e fluorescence of the peptide 11-24 suggests that the Trp 13 residue m ay appear in two types of situations: (a) in aqueous solution and (b) within a globular structure. Its CD spectra show that the tryptophan r esidue exists in both cases in a highly asymmetric environment indepen dent of the pH. (C) 1995 John Wiley & Sons, Inc.