Disulfides structure prediction

IL-2 is a 15.5-kDa protein of 133 amino acids (385). A disulfide bond between Cys58 and CyslOS is essential for bioactivity, whereas glycosylation does not seem to be important (386). A 3D structure for IL-2 has been solved to 3.0-A resolution (387), indicating that this cytokine is composed of a fourfold bundle cf amphipathic antiparallel a-helices. A modification of this structure has been proposed based on secondary structure prediction and comparison with other cytokines (388). 

An example of the positive deviation from Raoult s law is a solution made of acetone (CH3COCH3) and carbon disulfide (CS2). (a) Draw Lewis structures of these molecules. Explain the deviation from ideal behavior in terms of intermolecular forces, (b) A solution composed of 0.60 mole of acetone and 0.40 mole of carbon disulfide has a vapor pressure of 615 mmHg at 35.2°C. What would be the vapor pressure if the solution behaved ideally The vapor pressure of the pure solvents at the same temperature are 349 mmHg for acetone and 501 mmHg for carbon disulfide, (c) Predict the sign of AT/join-... 

The second application of the CFTI protocol is the evaluation of the free energy differences between four states of the linear form of the opioid peptide DPDPE in solution. Our primary result is the determination of the free energy differences between the representative stable structures j3c and Pe and the cyclic-like conformer Cyc of linear DPDPE in aqueous solution. These free energy differences, 4.0 kcal/mol between pc and Cyc, and 6.3 kcal/mol between pE and Cyc, reflect the cost of pre-organizing the linear peptide into a conformation conducive for disulfide bond formation. Such a conformational change is a pre-requisite for the chemical reaction of S-S bond formation to proceed. The predicted low population of the cyclic-like structure, which is presumably the biologically active conformer, agrees qualitatively with observed lower potency and different receptor specificity of the linear form relative to the cyclic peptide. 

Example V The Rearrangement FSSF - F S=S and the Predicted Nonexistence of 0195=8 and H9S=S. So far, conformers (Example I), isomers (Example II) and structural changes on one-electron oxidation (Example III and IV) have been dealt with. Another step in the direction of increasing complexity are those rearrangements, in which an atom is moved from one molecular site to another one, exemplified here by the isomerization of simple disulfides (33, 34) ... 

Structures of this type were generated in the reaction of Af-acyloxy-Af-alkoxyamides with thiols. Treatment of Ai-acetoxy-iV-butoxybenzamide (145, R = Bu, = Me) and a series of Ai-benzoyloxy-Ai-benzyloxybenzamides (139) with cysteine derivatives generated disulfides and hydroxamic esters (Section IV.C.3.b, Scheme 24). The intermediate Ai-alkoxy-Ai-thioalkylamides were unstable under the reaction conditions, reacting with a second thiol molecule at sulfur. The reaction of thiols at the anomeric nitrogen of Af-acyloxy-Ai-alkoxyamides has been modelled theoretically and is predicted to be favourable energetically, leading to a stable substitution product ... 

---