Fig. 1.

Illustrative comparative analysis of the wrapping of backbone hydrogen bonds of pea leghemoglobin (A) and human hemoglobin β-subunit (B). The chain backbone is represented as a virtual-bond polygonal joining α-carbons. Dehydrons computed following ref. 10 are indicated as green segments joining nonadjacent α-carbons, whereas properly desolvated backbone hydrogen bonds are shown as gray segments. Whereas the pea folding domain is a perfect wrapper of its backbone and is monomeric, the tetrameric human ortholog possesses the dehydrons associated with pairs (5,9), (90,94), and (90,95). The first dehydron is adjacent to E6, the sickle-cell anemia mutation site, and is located at the protein–protein interface Glu-6-(Phe-85, Leu-88) in the deoxy fiber. The other two dehydrons are determinants of the quaternary organization (6, 10).