230

15

The Molecules of Life

Fig. 15.6 Hydrogen-bonding capabilities of the peptide backbone and the polar residues (after

Baker and Hubbard). Residues not shown are incapable of hydrogen bond formation

The other main structural element is the betaβ-sheet, in which the H-bonds are formed

between peptides distant along the chain.¹⁰

The formation of these H-bonds has to, and does, take place in the presence of

a huge excess of water, and epistructural tension exists at the protein–water inter-

face.¹¹ Water is an excellent donor and acceptor of H-bonds and strongly com-

petes for the intraprotein ones. Successful folding therefore depends on the ability

of the protein to isolate the structurally important H-bonds from water; structural

10 As shown in Fig. 15.6, some residues can also participate in hydrogen-bonding, but the backbone

peptide H-bonds (or potential H-bond donors and acceptors) are of course more numerous and,

hence, more significant.

11 Fernández (2012a, b).