Two-state cooperativity in helix-coil transitions

Possibly the simplest representation for a two-state folding transition of a peptide is the crystallization into helical stmctures. Since most proteins possess hehcal segments, the heluc coil transition is perhaps the most prominent stmcture formation process of proteins. Helices form, if the values of the dihedral angles ijf and (p (see Fig. 1.6) of amino acids adjacent in the sequence lie within a certain section of the Ramachandran map. The boundaries of this section are not well defined, but most amino acids in hehcal state are found with dihedral angles in the intervals (p e (—90°, —30°) and jr e (—77°, —17°) [223]. 

Protein folding channels and kinetics of two-state folding 

Same quantities as in Fig. 9.15, but for the three-helix bundle 3D. From [226]. 

It is commonplace that secondary stmctures require the formation of dipolar hydrogen bonds. Whereas hydrogen bonds are doubtless necessary to stabilize secondary structures, 

---