Insulin solution structure

In crystal structures the two chains of insulin form highly ordered globular structures (8). Two main structural types form depending on crystallization conditions. In both structures the A-chains form two CC-helical segments, from residues Al—A8 and A13—A19, which are connected by a turn. In the structure referred to as the T-state, the B-chain contains two regions of extended chain, Bl—B8 and B21—B30, connected by an Ot-helix from B9-B19. In the R-state structure, the B-chain helix extends from Bl—B19. The crystallographic T-state structure best matches the solution structure of insulin determined by nmr (9), although the R-state can be induced in solution under the appropriate conditions. The surface of insulin which interacts with the insulin receptor includes the N- and C-termini of the A-chain and the C-terminus of the B-chain. 

Pyridine 2,6-dicarboxylic acid (dipic) also reacts favorably in a tridentate manner with vanadate to form a distorted trigonal bipyramidal complex [60], Multinuclear NMR studies of the complex in aqueous solution were consistent with the formation of only one complex (-533 ppm) that was monoanionic and had VL stoichiometry and a solution structure that corresponded to the crystalline compound [61], A pH variation study of a sample (10 mM in H20) prepared from the crystalline material showed that this complex is stable over a very wide pH range. Although it was almost fully dissociated at pH 7.3, the complex regenerated at lower pH and was almost fully formed at pH 6. At pH 0.4, it was partially dissociated to cationic vanadate but was still about half formed at pH 0.3 [61], One of the reasons for the extended range under strongly acidic conditions is the fact that the complex can be protonated and has a pKa very close to 0. This compound is a well-known insulin-... 

Solution structures of the R-6 human insulin hexamer. Biochemistry, 36, 9409-9422. 

In the case of Msp A, microspheres were prepared in a mild environment that is, an organic solvent and a high shear were absent. A circular dichroism (CD) spectrum of insulin released from Msp A was virtually identical to that of a freshly prepared native insulin solution. This means that the released insulin preserved its secondary structure. In contrast, the CD spectrum for Msp B indicated a loss of secondary structure integrity due to both the use of dichloro-methane and the harsh preparation conditions employed (48). 

Solution Structures of Insulin-Enhancing Vanadium(IV) Complexes... 

Insulin binding to the extracellular side of cell membranes initiates the insulin cascade , a series of phosphorylation/dephosphorylation steps. A postulated mechanism for vanadium is substitution of vanadate for phosphate in the transition state structure of protein tyrosine phosphatases (PTP).267,268 In normal physiological conditions, the attainable oxidation states of vanadium are V111, Viv and Vv. Relevant species in solution are vanadate, (a mixture of HV042-/ H2VOO and vanadyl V02+. Vanadyl is not a strong inhibitor of PTPs, suggesting other potential mechanisms for insulin mimesis for this cation. 

Physical properties of the protein structure should be considered in designing strategies to achieve stable formulations because they can often yield clues about which solution environment would be appropriate for stabilization. For example, the insulin molecule is known to self-associate via a nonspecific hydrophobic mechanism66 Stabilizers tested include phenol derivatives, nonionic and ionic surfactants, polypropylene glycol, glycerol, and carbohydrates. The choice of using stabilizers that are amphiphilic in nature to minimize interactions where protein hydrophobic surfaces instigate the instability is founded upon the hydro-phobic effect.19 It has already been mentioned that hydrophobic surfaces prefer... 

Before we take leave of primary structures for proteins, there is one last, important realization. Proteins serving the same function in different species may have different primary structures. For example, the primary structures of bovine, ovine, and human insulins are not quite the same. They are closely related but not identical. Different species have discovered different protein solutions for the same biological problem. 

The crystal structure of this protein has been shown to depend on the salt solution from which it is crystallized.45 When crystallized from (NH4)2S04, the insulin hexamer is held together in part by two Zn2+ ions. These can be visualized as being at either end of a cylinder, and each Zn2 has as a ligand one histidine imidazole nitrogen atom from one of three chains. Thus a histidine (his B.10) of each of the six chains is coordinated to Zn2+, three at each Zn2+. The Zn2+ ions occupy octahedral (trigonally distorted) sites overall. 

The overall fold of a globular protein molecule in solution is likely to be given by the X-ray structure of the molecule in a crystal. This has been shown to be the case in detail for one protein, lysozyme, by means of nuclear magnetic resonance techniques, and is highly probable for others. It is necessary, however, to be aware that the conditions under which the protein is crystallized, or studied in solution, can affect the fold, and this has been illustrated with insulin. 

Hodgkin s third major project was determining the structure of the protein insulin. It was only technical advances in the 1960s that made the solution finally possible. When the results were published in 1969, the researchers were listed in alphabetical order, showing her willingness to share credit and her egalitarian attitude toward all research workers. 

There is a rich literature for the determination of these symmetry families [31], and this might be of use in the back-translation problem. In any case, for structural unidentifiability caused by conserved moieties the back-translation may be formulated by simple linear combinations [3, 6]. Another special case where improved solutions of the back-translation problem are possible is term elimination and lumping [6] examples of both these cases in the model for insulin signaling are provided in the next section. First, however, we must consider the back-translation problem in the example introduced above. 

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