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As part of a study into the homo- and hetero-oligomerization properties of muscle-specific transcriptional factors, and their interation with DNA, sedimentation equilibrium studies, accompanied by circular dichroism measurements, have been made on peptides derived from the helix-loop-helix regions of MyoD and E47. In addition, a chimeric peptide, in which residues from the loop region of E47 were substituted into that of MyoD, a fluorescently labelled derivative of the MyoD-bHLH peptide and a disulphide crosslinked version of MyoD-bHLH have also been investigated. MyoD-bHLH has been found to form a monomer tetramer equilibrium in the µM concentration range, while E47-bHLH exists as a highly associated dimer. The MyoD-bHLH derivatives appear to exhibit the same oligomerization behavior as their MyoD-bHLH parent. CD studies of the disulphide-crosslinked peptide show that a level of organization higher than that of the dimer is required for structural stability in the MyoD-bHLH system. The rôle of self-association in the context of the biological function of these peoteins is discussed. [ABSTRACT FROM AUTHOR]

Protein-protein recognition and protein oligomerization functions are among the important roles played by the α-helical coiled coil motif. As part of a study into the equilibrium and kinetic aspects of the folding of model coiled coils, an investigation into the stoichiometry and magnitude of the associative constants by sedimentation equilibrium in the ultracentrifuge has been initiated. A series of interrelated model peptides, with sequence lengths of about 30 residues, has been designed, synthesized and characterized. Each of the peptides has been subjected to conventional sedimentation equilibrium analysis under a variety of conditions. The stoichiometry of self-association has been established and it has been shown that, contrary to the expected result, most of the peptides formed trimeric systems of varying stability. The effect of substituting large hydrophobic constituents of the interacting interfaces of the systems with other similar residues has been shown to have minimal effect on trimer formation. However, substitution of such residues in the central sequence positions with either alanine or asparagine leads to a marked decrease in the stability of the trimeric state. [ABSTRACT FROM AUTHOR]