Multiple native-like conformations trapped via self-association-induced hydrophobic collapse of the 33-residue beta-sheet domain from platelet factor 4.
Native platelet factor 4 (PF4) (70 residues) has a hydrophobic three-stranded anti-parallel beta-sheet domain on to which is folded an amphipathic C-terminal alpha-helix and an aperiodic N-terminal domain. The 33-amino acid beta-sheet domain from PF4 (residues 23-55) has been synthesized and studied by c.d. and n.m.r. At 10 degrees C and low concentration, peptide 23-55 appears to exist in aqueous solution in a random-coil distribution of highly flexible conformational states. Some preferred conformation, however, is observed, particularly within a relatively stable chain reversal from Leu-45 to Arg-49. As the peptide concentration and/or temperature is increased, a new conformational state(s) appears and intensifies as slowly exchanging (600 MHz 1H-n.m.r. chemical-shift time scale) random-coil resonances disappear. Hill plots of the concentration-dependence indicated mostly tetramer formation as found in native PF4. Although apparent resonance linewidths in aggregate state(s) are of the order of 100 Hz, sequence-specific assignments for most resonances could be made. N.m.r./nuclear Overhauser effect structural analysis indicates the formation of multiple native-like anti-parallel beta-sheet conformations, kinetically trapped via subunit-association-induced hydrophobic collapse and stabilized by low-dielectric electrostatic interactions among/between Gly-28 and Lys-50 in opposing subunits. Results are discussed in terms of protein folding.
Ilyina
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Department of Biochemistry, University of Minnesota, Minneapolis 55455.
Mayo
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D000595:Amino Acid Sequence; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002942:Circular Dichroism; D004563:Electrochemistry; D006801:Humans; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010978:Platelet Factor 4 / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary
D046911:Macromolecular Substances; D010978:Platelet Factor 4