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Magnetic Tweezers for the Measurement of Twist and Torque
Published on: May 19, 2014
Molecular characterization of helix-loop-helix peptides
S J Anthony-Cahill1, P A Benfield, R Fairman
1Biotechnology Department, DuPont Merck Pharmaceutical Co., Wilmington, DE 19880-0328.
Abstract:
A class of regulators of eukaryotic gene expression contains a conserved amino acid sequence responsible for protein oligomerization and binding to DNA. This structure consists of an arginine- and lysine-rich basic region followed by a helix-loop-helix motif, which together mediate specific binding to DNA. Peptides were prepared that span this motif in the MyoD protein; in solution, they formed alpha-helical dimers and tetramers. They bound to DNA as dimers and their alpha-helical content increased on binding. Parallel and antiparallel four-helix models of the DNA-bound dimer were constructed. Peptides containing disulfide bonds were engineered to test the correctness of the two models. A disulfide that is compatible with the parallel model promotes specific interaction with DNA, whereas a disulfide compatible with the antiparallel model abolishes specific binding. Electron paramagnetic resonance (EPR) measurements of nitroxide-labeled peptides provided intersubunit distance measurements that also supported the parallel model.
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