Ligand-induced transition in conformations of vicinal cysteine disulfides in proteins.

Vicinal cysteine disulfides are thought to be associated with specific conformations of cysteine disulfides due to the restricted rotation of single bonds in an eight-membered cyclic disulfide loop. Conformations of vicinal cysteine disulfides are analyzed using χ1 , χ2 , χ3 , χ2 ', χ1 ' torsion angles in the crystal structures of proteins retrieved from Protein Data Bank (PDB). 85% of vicinal disulfides have (+, -)LHStaple conformation with trans configuration of the peptide bond and 9% have (-, -)RHStaple conformation with cis configured peptide bond. Conformational analysis of dipeptide Cys-Cys vicinal disulfide by density functional theory (DFT) further supported (+, -)LHStaple, (-, -)RHStaple, and (+, +)RHStaple as the preferred conformations of vicinal disulfides. Interestingly, the rare conformations of vicinal disulfides are observed in the ligand-bound forms of proteins and have higher disulfide strain energy. Conformations of vicinal disulfides in palmitoyl protein thioesterase 1, AChBP, and α7 nicotinic receptor are changed from preferred (+, -)LHStaple to rare (+, -)AntiLHHook/(+, -)AntiRHHook/(+, +)RHStaple conformation due to binding of ligands. Surprisingly, ligands are proximal to the vicinal disulfides in protein complexes that exhibited rare conformations of vicinal disulfides. The report has identified (+, -) LHStaple/(-, -) RHStaple as the hallmark conformations of vicinal disulfides and unraveled ligand-induced transition in conformations of vicinal cysteine disulfides in proteins.

Conformations of cysteine disulfides of peptide toxins: Advantage of differentiating forward and reverse asymmetric disulfide conformers.

Conformations of cysteine disulfides were analyzed in X-ray, nuclear magnetic resonance (NMR), and co-crystal structures of peptide toxins retrieved from Protein Data Bank. The parameters side chain torsional angles, disulfide strain energy, interatomic Cα/Cß distances, and Ramachandran angles were used as probes to derive conformational features of cysteine disulfides. Schmidt, Ho, and Hogg ( 2006 ) Allosteric disulfide bonds. Biochemistry, 45, 7429-7433 scheme was adapted to classify the disulfide conformations of peptide toxins. Anomalies were observed while treating "forward" and "reverse" asymmetric disulfide conformers as same disulfide conformation in peptide toxins. Thus, new scheme was proposed to classify "forward" and "reverse" asymmetric disulfide conformers separately. Total available conformers space for classification of toxins disulfides is 32. Interestingly, all 32 disulfide conformations are observed in peptide toxins. -LHSpiral is predominant disulfide conformation of peptide toxins. Significant variations were observed in population of occurrence of disulfide conformers, disulfide strain energy, and distribution of DCα-Cα and DCß-Cß values between X-ray, NMR, and co-crystal structures of peptide toxins. The observed differences in conformations of disulfides of same peptide toxins between different states were used as platform to demonstrate advantage of differentiating forward and reverse asymmetric disulfide conformers. Newly proposed scheme allows accurate representation of true conformational diversity of disulfides between X-ray and NMR structures of same peptide toxins. Newly proposed scheme also permits to derive additional structural information from nomenclature which was illustrated by comparing conformations of disulfides between unbound and bound form of toxin with channel/receptor. The results will be of interest for growing field of structural venomics and conformational analysis of peptide/protein disulfides. Communicated by Ramaswamy H. Sarma.

Glutathione as a photo-stabilizer of avobenzone: an evaluation under glass-filtered sunlight using UV-spectroscopy.

Avobenzone is the most widely used UVA filter in sunscreen lotion and it is prone to degradation in the presence of sunlight/UV radiation. To overcome the photo-instability of avobenzone, various photostabilizers have been used as additives, including antioxidants such as vitamin C, vitamin E, and ubiquinone. In the present study, the well known antioxidant, glutathione, was evaluated for protecting avobenzone from photodegradation in the presence of glass-filtered sunlight. The features of glutathione as a skin whitener and a radical scavenger in cells have prompted the assessment of the photostabilzing activity of glutathione on avobenzone. Glutathione significantly attenuated the glass-filtered sunlight-induced degradation of avobenzone at equimolar or higher ratios of glutathione and avobenzone. Mutational studies have been undertaken to investigate the role of the thiol group and the isopeptide bond of glutathione on its photoprotection activity towards avobenzone. The thiol group of glutathione plays a vital role in exhibiting the photoprotection activity, which was further supported by the studies on photodegradation of avobonzone in the presence of ß-mercaptoethanol. The dual role of glutathione as a skin whitening agent and a photostabilizer of avobenzone may be useful for the development of multipurpose cosmetic lotions.

Structural space of intramolecular peptide disulfides: Analysis of peptide toxins retrieved from venomous peptide databases.

Structural space of intramolecular peptide disulfides is the combination of arrangement of even number of cysteine residues in single polypeptide and the disulfide isomers resulting from differential connectivity between cysteine residues. In the current report, we are documenting theoretical analysis and derivation of general formula [2×4{(n2)-1}] to predict possible distinct cysteine patterns for given 'n' even number of cysteine residues in a sequence. Combined formula of predicting distinct cysteine patterns and different disulfide isomers can be used to deduce the truly available structural space of intramolecular peptide disulfides, which may be used in structural analysis of disulfide rich peptides and proteins. In this report, we have also analyzed cysteine patterns and disulfide connectivities of peptide toxins, which is the largest group of intramolecular peptide disulfide natural products, retrieved from publically available animal toxin databases. Observed 29 distinct cysteine patterns of toxins exhibited 61 unique intramolecular disulfide folds, with limitation of having up to eight cysteine residues in a sequence, compared to theoretically available 170 different cysteine patterns generating 13,946 distinct intramolecular disulfide folds. Database analysis of peptide toxins has also revealed the features of presence of same intramolecular disulfide motif in functionally divergent peptide toxins and adaptation of the same disulfide fold with similar functions in different venomous species. Calculations of relative accessible surface area of cystine and average value of non-cysteine residues in the representative intramolecular disulfide folds of peptide toxins has revealed the feature of poor accessibility of cystine to external agents and their dependency on number of disulfide bonds in the sequence. Implementation of new generation sequencing methods and novel disulfide mapping techniques will unravel hidden diversity of intramolecular disulfide motifs of toxins and current report points to the selection of disulfide motifs in peptide toxins.