HelixLoopHelix
Helix-loop-helix (HLH) is a common protein structural motif characterized by two alpha helices connected by a short loop. The HLH region frequently appears as part of larger domains in a broad range of eukaryotic proteins, most notably transcription factors. The motif promotes protein–protein interactions, particularly dimerization, which is essential for the function of many HLH-containing proteins. In many cases, a basic region adjacent to the HLH enables DNA binding and helps define target specificity.
When a basic region is present, the motif is referred to as basic helix-loop-helix (bHLH). The basic
Structure and dynamics: In the HLH region, helices 1 and 2 form a coiled-coil-like interface stabilized by
Biological roles and examples: bHLH transcription factors regulate development and differentiation, including muscle differentiation (MyoD, myogenin),