title: Structural space of intramolecular peptide disulfides: Analysis of peptide toxins retrieved from venomous peptide databases.
abstract: 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.
authors.affiliation: Department of Chemistry, School of Chemical Sciences, Central University of Karnataka, Kalaburagi, 585367, Karnataka, India.
authors.forename: Panchada Ch V
authors.initials: PCV
authors.lastname: Govindu
authors.affiliation: IAS-INSA-NASI Summer Research Fellow, Department of Chemistry, School of Chemical Sciences, Central University of Karnataka, Kalaburagi, 585367, Karnataka, India.
authors.forename: Priyanka
authors.initials: P
authors.lastname: Chakraborty
authors.affiliation: IAS-INSA-NASI Summer Research Fellow, Department of Chemistry, School of Chemical Sciences, Central University of Karnataka, Kalaburagi, 585367, Karnataka, India.
authors.forename: Angshu
authors.initials: A
authors.lastname: Dutta
authors.affiliation: Department of Chemistry, School of Chemical Sciences, Central University of Karnataka, Kalaburagi, 585367, Karnataka, India. Electronic address: khgowd@cuk.ac.in.
authors.forename: Konkallu Hanumae
authors.initials: KH
authors.lastname: Gowd
mesh_terms: D030562:Databases, Protein; D004220:Disulfides / Q000737:chemistry*; D015394:Molecular Structure; D010455:Peptides / Q000737:chemistry*; D014118:Toxins, Biological / Q000032:analysis*; D014688:Venoms / Q000737:chemistry*
chemical_list: D004220:Disulfides; D010455:Peptides; D014118:Toxins, Biological; D014688:Venoms
keywords: Diversity of cysteine pattern; Inhibitory Cystine Knot motif; Intramolecular peptide disulfides; Peptide disulfide isomers; Peptide toxin; Venomous peptide databases