Secondary Valence Forces Are the Glue That Holds Polypeptide Chains Together

Secondary Valence Forces Are the Glue That Holds Polypeptide Chains Together 

The studies of Anfinsen not only showed that folding can be a spontaneous process predetermined by the primary amino acid sequence, but they suggested that folded structures are thermodynamically more stable. Thus the folding of globular proteins should be understandable in terms of the types of forces that exist between polypeptide chains and water. 

Hydrogen Bonds. Many characteristics of H bonds have already been discussed because of the major role they play in stabilizing fibrous proteins. Additional aspects of H bonds to be considered relate more closely to the structures of globular proteins. Evidence for the existence of an H bond comes from the observation of a decreased distance between donor and acceptor groups forming the H bond. 

Thus from the van der Waals radii given in table 4.1, we can calculate the distances between nonbonded H and O atoms (2.6 A) and between nonbonded H and N atoms (2.7 A). When an H bond is present, this distance is usually reduced by about 0.8 A in both cases. Some important H-bond donors and acceptors are shown in figure 4.3. 

Van der Waals Forces. Van der Waals interactions are of two types one attractive and one repulsive. Attractive van der Waals forces involve interactions among induced dipoles that arise from fluctuations in the electron charge densities of neighboring nonbonded atoms. Such interactions amount to 0.1-0.2 kcal/mol despite their small size, the large number of such interactions that occur when molecules come close together makes such interactions quite significant. Van der Waals forces favor close packing in folded protein structures. 

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Visualizing Folded Protein Structures Primary Structure Determines Tertiary Structure Secondary Valence Forces Are the Glue That Holds Polypeptide Chains Together Domains Are Functional Units of Tertiary Structure Predicting Protein Tertiary Structure Quaternary Structure Involves the Interaction of Two or More Proteins... 

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