(a) Pattern of UWHBs, represented as green segments joining paired α-carbons, for human Hb β-subunit. (a) Pattern of UWHBs, represented as green segments joining paired α-carbons, for human Hb β-subunit. The virtual-bond chain backbone is shown schematically as a blue polygonal joining α-carbons. The sufficiently wrapped hydrogen bonds are indicated as gray segments joining the α-carbons of the paired residues. (b) Ribbon display for human Hb. Ariel Fernández et al. PNAS 2003;100:11:6446-6451 ©2003 by National Academy of Sciences