Design, synthesis, and conformational studies of the hGM-CSF derived peptide (13-27)-Gly-(75-87)

An analogue of the human granulocyte-macrophage colony-stimulating factor ( hGM-CSF), hGM-CSF(13-27)-Gly-(75-87) was synthesized by solid phase methodo logy. This analogue was designed to comprise helices A and C of the native growth factor linked by a glycine bridge. Helices A and C form half of a fo ur-helix bundle motif in the crystal structure of the native factor and ale involved in the interaction with alpha- and beta-chains of the heterodimer ic receptor. A conformational analysis of the synthetic analogue by CD, two ;dimensional nmr spectroscopy, and molecular dynamics calculations is repor ted The analogue is in a random structure in water and assumes a partially alpha-helical conformation in a 1 : 1 trifluoroethanol/water mixture. The h elix content in this medium is similar to 70%. By 2D-nmr spectroscopy, two helical segments were identified in the sequences corresponding to helices A and C. In addition to medium and short-range NOESY connectivities. a long -range cross peak was found between the CP proton of val(16) and NH proton of His(87) (using the numbering of the native protein). Experimentally deri ved interproton distances were used as restraints in molecular dynamics cal culations, utilizing the x-ray coordinates as the initial structure. The fi nal structure is characterized by two helical segments in close spatial pro ximity, connected by. a loop region. This structure is similar to that of t he corresponding domain in the x-my structure of the native growth factor i n which helices A and C are oriented in an antiparallel fashion. The N-term inal residues Gly-Pro of helix C ate involved in an irregular rum connectin g the two helical segments. As a consequence, helix C is appreciably shifte d and slightly rotated with respect to helix A compared to the x-mp structu re of the native growth factor These small differences in the topology of t he two helices could explain the lower biological activity of this analogue with respect to that of the native growth factor. (C) 1999 John Wiley & So ns, Inc.