Hydrogen bonding globular proteins

Baker E N and Flubbard R E 1984 Hydrogen bonding in globular proteins Prog. Biophys. Molec. Biol. 44 97-179... 

Hydrogen bonding stabilizes some protein molecules in helical forms, and disulfide cross-links stabilize some protein molecules in globular forms. We shall consider helical structures in Sec. 1.11 and shall learn more about ellipsoidal globular proteins in the chapters concerned with the solution properties of polymers, especially Chap. 9. Both secondary and tertiary levels of structure are also influenced by the distribution of polar and nonpolar amino acid molecules relative to the aqueous environment of the protein molecules. Nonpolar amino acids are designated in Table 1.3. 

Equation (8.97) shows that the second virial coefficient is a measure of the excluded volume of the solute according to the model we have considered. From the assumption that solute molecules come into surface contact in defining the excluded volume, it is apparent that this concept is easier to apply to, say, compact protein molecules in which hydrogen bonding and disulfide bridges maintain the tertiary structure (see Sec. 1.4) than to random coils. We shall return to the latter presently, but for now let us consider the application of Eq. (8.97) to a globular protein. This is the objective of the following example. 

Figure 26.5 (a) The o-helical secondary structure of proteins is stabilized by hydrogen bonds between the N—H group of one residue and the C=0 group four residues away, (b) The structure of myoglobin, a globular protein with extensive helical regions that are shown as coiled ribbons in this representation. 

The enzymes are protein molecules having globular structure, as a rule. The molecular masses of the different enzymes have values between ten thousands and hundred thousands. The enzyme s active site, which, as a rule, consists of a nonproteinic organic compound containing metal ions of variable valency (iron, copper, molybdenum, etc.) is linked to the protein globule by covalent or hydrogen bonds. The catalytic action of the enzymes is due to electron transfer from these ions to the substrate. The protein part of the enzyme secures a suitable disposition of the substrate relative to the active site and is responsible for the high selectivity of catalytic action. 

Baker, E. N., and Hubbard, R. E. (1984). Hydrogen bonding in globular proteins. Prog. 

It is the sequence and types of amino acids and the way that they are folded that provides protein molecules with specific structure, activity, and function. Ionic charge, hydrogen bonding capability, and hydrophobicity are the major determinants for the resultant three-dimensional structure of protein molecules. The a-chain is twisted, folded, and formed into globular structures, a-helicies, and P-sheets based upon the side-chain amino acid sequence and weak intramolecular interactions such as hydrogen bonding between different parts of the peptide... 

The p-pleated sheet structure occurs in fibrous as well as globular proteins and is formed by intermolecular hydrogen bonds between a carboxyl group oxygen of one amino acid and an amine hydrogen of an adjacent polypeptide chain. Parallel p-pleated sheets form when the adjacent polypeptide chains are oriented in one direction (from N-terminal to C-terminal end or vice versa). Antiparallel p-pleated... 

Nature uses globular protein domains to bind sulfate and phosphate anions using respectively 7 and 12 complementary anion-hydrogen bond arrangements. With this in mind we decided to construct new, neutral ferrocene derivatives that contain various hydrogen bond donor and acceptor sites for anion recognition. 

The native conformation of proteins is stabilized by a number of different interactions. Among these, only the disulfide bonds (B) represent covalent bonds. Hydrogen bonds, which can form inside secondary structures, as well as between more distant residues, are involved in all proteins (see p. 6). Many proteins are also stabilized by complex formation with metal ions (see pp. 76, 342, and 378, for example). The hydrophobic effect is particularly important for protein stability. In globular proteins, most hydrophobic amino acid residues are arranged in the interior of the structure in the native conformation, while the polar amino acids are mainly found on the surface (see pp. 28, 76). 

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