Chain structures hydrogen bonding cooperativity

Chains of cooperative hydrogen bonds are commonly seen in crystal structures of mono- and oligosaccharides. Shown below is a picture of the crystal structure of /)-nitrophenyl a-maltohexaoside. A long running chain of hydrogen bonds can be identified along the 2,3-vicinal... 

Favor hydrogen bond structures in which three-center bonds cross-link their chains and loops into nets and thereby enhance cooperativity (47). 

Many proteins consist of a single polypeptide chain, and are defined as monomeric proteins. However, others may consist of two or more polypeptide chains that may be structurally identical or totally unrelated. The arrangement of these polypeptide subunits is called the quaternary structure of the protein. [Note If there are two subunits, the protein is called dimeric , if three subunits trimeric , and, if several subunits, multimeric. ] Subunits are held together by noncovalent interactions (for example, hydrogen bonds, ionic bonds, and hydrophobic interactions). Subunits may either function independently of each other, or may work cooperatively, as in hemoglobin, in which the binding of oxygen to... 

Fig. 5. Protein folding. The unfolded polypeptide chain collapses and assembles to form simple structural motifs such as p-sheets and a-helices by nucleation-condensation mechanisms involving the formation of hydrogen bonds and van der Waal s interactions. Small proteins (eg, chymotrypsin inhibitor 2) attain their final (tertiary) structure in this way. Larger proteins and multiple protein assemblies aggregate by recognition and docking of multiple domains (eg, p-barrels, a-helix bundles), often displaying positive cooperativity. Many noncovalent interactions, including hydrogen bonding, van der Waal s and electrostatic interactions, and the hydrophobic effect are exploited to create the final, compact protein assembly. Further structural...

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