1H-NMR evidence for two buried ASN side-chains in the c-Myc-Max heterodimeric α-helical coiled-coil

Abstract

Publisher Summary A dimerization motif—The Leucine Zipper (LZ)—is found in the b-LZ and b-HLH-LZ transcription factor families. In the b-LZ family, for example, GCN4 and c-Jun, Asn residues are found to be conserved at a certain position termed as “ a ” in the heptad reapeat. A pair of Asn side-chains destabilizes the homodimeric LZ coiled-coil compared to hydrophobic side-chains otherwise conserved at this position. The two Asn side-chains found at position a is likely to contribute to heterodimerization specificity by destabilizing Max homodimeric LZ. From the data presented in the chapter, it appears that Max Asn19 a can form interhelical side-chain–main-chain H-bonds. The results indicate that the two Asn side-chains found on the Max LZ are buried at the interface of the c-Myc-Max heterodimeric LZ. In other words, this chapter describes NOEs between the Hδ protons of both Asn side-chains and protons from the residues forming the holes in which they are predicted to pack on the c-Myc LZ. It reports an NOE between Max Asn19 a Hz proton and c-Myc Arg19 a backbone NH and slow deuterium exchange for both of Max Asn 19a H5 protons. These results support the proposition based on molecular modeling that this Asn side-chain forms H-bonds with the backbone carbonyl of c-Myc Leu15 d and the backbone NH of c-Myc Arg19 a .