Multi-class cyanobacterial toxin analysis using hydrophilic interaction liquid chromatography-mass spectrometry.

Cyanobacteria produce diverse classes of toxins including microcystins, nodularins, anatoxins, cylindrospermopsins and saxitoxins, encompassing a range of chemical properties and mechanisms of toxicity. Comprehensive analysis of these toxins in cyanobacterial, environmental and biological samples generally requires multiple methods of extraction and analysis. In this work, a method was developed for the major classes of cyanotoxins, which comprised of a three-step liquid-solid extraction method using 75 % CHCN with 0.

The Common Sunstar -A Neurotoxic Starfish.

Saxitoxins (STXs) are a family of potent neurotoxins produced naturally by certain species of phytoplankton and cyanobacteria which are extremely toxic to mammalian nervous systems. The accumulation of STXs in bivalve molluscs can significantly impact animal and human health. Recent work conducted in the North Sea highlighted the widespread presence of various saxitoxins in a range of benthic organisms, with the common sunstar () demonstrating high concentrations of saxitoxins.

Hydrophilic interaction liquid chromatography-tandem mass spectrometry for quantitation of paralytic shellfish toxins: validation and application to reference materials.

Paralytic shellfish toxins (PSTs) are potent neurotoxins produced by marine dinoflagellates that are responsible for paralytic shellfish poisoning (PSP) in humans. This work highlights our ongoing efforts to develop quantitative methods for PSTs using hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS). Compared with the commonly used method of liquid chromatography with post-column oxidation and fluorescence detection (LC-ox-FLD), HILIC-MS/MS has the potential of being more robust, sensitive and straightforward to operate, and provides unequivocal confirmation of toxin identity.

Tunable control of polyproline helix (PPII) structure via aromatic electronic effects: an electronic switch of polyproline helix.

Aromatic rings exhibit defined interactions via the unique aromatic π face. Aromatic amino acids interact favorably with proline residues via both the hydrophobic effect and aromatic-proline interactions, C-H/π interactions between the aromatic π face and proline ring C-H bonds. The canonical aromatic amino acids Trp, Tyr, and Phe strongly disfavor a polyproline helix (PPII) when they are present in proline-rich sequences because of the large populations of cis amide bonds induced by favorable aromatic-proline interactions (aromatic-cis-proline and proline-cis-proline-aromatic interactions).

Proline editing: a general and practical approach to the synthesis of functionally and structurally diverse peptides. Analysis of steric versus stereoelectronic effects of 4-substituted prolines on conformation within peptides.

Functionalized proline residues have diverse applications. Herein we describe a practical approach, proline editing, for the synthesis of peptides with stereospecifically modified proline residues. Peptides are synthesized by standard solid-phase peptide synthesis to incorporate Fmoc-hydroxyproline (4R-Hyp).

Rapid postcolumn methodology for determination of paralytic shellfish toxins in shellfish tissue.

A rapid liquid chromatographic (LC) method with postcolumn oxidation and fluorescence detection (excitation 330 nm, emission 390 nm) for the determination of paralytic shellfish toxins (PSTs) in shellfish tissue has been developed. Extracts prepared for mouse bioassay (MBA) were treated with trichloroacetic acid to precipitate protein, centrifuged, and pH-adjusted for LC analysis. Saxitoxin (STX), neoSTX (NEO), decarbamoylSTX (dcSTX), and the gonyautoxins, GTX1, GTX2, GTX3, GTX4, GTX5, dcGTX2, and dcGTX3, were separated on a polar-linked alkyl reversed-phase column using a step gradient elution; the N-sulfocarbamoyl GTXs, C1, C2, C3, and C4, were determined on a C-8 reversed-phase column in the isocratic mode.

Electronic control of amide cis-trans isomerism via the aromatic-prolyl interaction.

The cis-trans isomerization of prolyl amide bonds results in large structural and functional changes in proteins and is a rate-determining step in protein folding. We describe a novel electronic strategy to control cis-trans isomerization, based on the demonstration that interactions between aromatic residues and proline are tunable by aromatic electronics. A series of peptides of sequence TXPN, X = Trp, pyridylalanine, pentafluorophenylalanine, or 4-Z-phenylalanine derivatives (Z = electron-donating, electron-withdrawing, or electron-neutral substituents), was synthesized and Ktrans/cis analyzed by NMR.

Effects of i and i+3 residue identity on cis-trans isomerism of the aromatic(i+1)-prolyl(i+2) amide bond: implications for type VI beta-turn formation.

Cis-trans isomerization of amide bonds plays critical roles in protein molecular recognition, protein folding, protein misfolding, and disease. Aromatic-proline sequences are particularly prone to exhibit cis amide bonds. The roles of residues adjacent to a tyrosine-proline residue pair on cis-trans isomerism were examined.

Proline editing: a divergent strategy for the synthesis of conformationally diverse peptides.

[reaction: see text] Strong conformational biases in peptides and proteins can be achieved with 4-substituted proline residues (cis-, trans-, or disubstituted fluoroproline or hydroxyproline). The practical, divergent synthesis of peptides containing these residues, via postsynthetic modification of a peptide containing an internal trans-hydroxyproline residue, is described. Significant differences in the conformations of the peptides Ac-TYXN-NH2 were observed, including K(trans/cis) values, which varied from 1.