Helical formation in isolated fragments of bovine growth hormone.
The peptide 109-133 was isolated from bovine growth hormone (bGH) and studied for helix formation in aqueous solutions. This fragment was shown to contain helical structure by far-ultraviolet circular dichroism in aqueous solutions. The amount of helix was dependent on pH and peptide concentration. The peptide has maximum helicity between pH 4 and 5 and at high peptide concentration. Under these conditions for maximal helix population, this fragment is approximately 100% helical. Secondary structure predictions suggest that residues 110-127 have a strong propensity to form an amphipathic helix. We have also studied a related peptide, 96-133, and show by gel filtration that it undergoes an increase in molecular weight that directly correlates with a coil to helix transition. A comparison of the helical content of 96-133 to 109-133 and circular dichroism studies of peptide 96-112 suggest that the helix of 96-133 is limited to the 109-133 region. Current models for alpha-helix formation predict that peptides the size of 109-133 should not contain measurable helicity in aqueous solutions. Our studies show that the unusual stability of helix 109-133 is due to electrostatic interactions and probable intermolecular packing between hydrophobic faces of the amphipathic surfaces of the helices. The implications of helix formation in these fragments to a framework model of protein folding for bGH are discussed.
Brems
D N
DN
Control Division, Upjohn Company, Kalamazoo, Michigan 49001.
Plaisted
S M
SM
Kauffman
E W
EW
Lund
M
M
Lehrman
S R
SR
D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D013006:Growth Hormone; D006863:Hydrogen-Ion Concentration; D010446:Peptide Fragments; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet
D010446:Peptide Fragments; D013006:Growth Hormone