Massively parallel sample preparation for the MALDI MS analyses of tissues.

Investigation of the peptidome of the nervous system containing large, often easily identifiable neurons has greatly benefited from single-cell matrix-assisted laser desorption/ionization (MALDI) mass spectrometry and has led to the discovery of hundreds of novel cell-to-cell signaling peptides. By combining new sample preparation methods and established protocols for bioanalytical mass spectrometry, a high-throughput, small-volume approach is created that allows the study of the peptidome of a variety of nervous systems. Specifically, approximately single-cell-sized samples are rapidly prepared from thin tissue slices by adhering the tissue section to a glass bead array that is anchored to a stretchable membrane.

Vitamin E imaging and localization in the neuronal membrane.

Vitamin E (alpha-tocopherol) has been implicated in several cellular processes including signaling, transport, lipid membrane curvature, and several neurodegenerative disorders. Vitamin E imaging has been hindered by the inaccessibility of the molecule to traditional immunohistochemical methods. Using time-of-flight secondary ion mass spectrometry (ToF-SIMS), the distribution of major constituents in the cellular membrane of isolated neurons was investigated.

MALDI-MS imaging of features smaller than the size of the laser beam.

The feasibility of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging of features smaller than the laser beam size has been demonstrated. The method involves the complete ablation of the MALDI matrix coating the sample at each sample position and moving the sample target a distance less than the diameter of the laser beam before repeating the process. In the limit of complete sample ablation, acquiring signal from adjacent positions spaced by distances smaller than the sample probe enhances image resolution as the measured analyte signal only arises from the overlap of the laser beam size and the non-ablated sample surface.

Imaging mass spectrometry: fundamentals and applications to drug discovery.

Imaging mass spectrometry (IMS) encompasses a variety of techniques that enable the chemical imaging of analytes, which range in size from atoms and small molecules to intact proteins, directly from biological tissues. IMS is transforming specific areas in biological research with its unique combination of chemical and spatial information. Innovations in instrumentation and imaging protocols will make this approach invaluable at many stages of the drug discovery process, including pharmacological target screening and evaluating the distribution of drug and drug metabolites in cells and tissues.

Further studies on the origins of asymmetric charge partitioning in protein homodimers.

Dissociation of gas-phase protonated protein dimers into their constituent monomers can result in either symmetric or asymmetric charge partitioning. Dissociation of alpha-lactalbumin homodimers with 15+ charges results in a symmetric, but broad, distribution of protein monomers with charge states centered around 8+/7+. In contrast, dissociation of the 15+ heterodimer consisting of one molecule in the oxidized form and one in the reduced form results in highly asymmetric charge partitioning in which the reduced species carries away predominantly 11+ charges, and the oxidized molecule carries away 4+ charges.

The role of acidic residues and of sodium ion adduction on the gas-phase H/D exchange of peptides and peptide dimers.

Gas-phase H/D exchange is widely used for characterizing the structure of ions. However, many structural parameters that affect the rate of H/D exchange are poorly understood, which complicates the interpretation of experimental data. Here, the effects of sodium ion adduction on the rate of H/D exchange with D2O for a series of peptides and peptide dimers with varying numbers of acidic residues are described.

Gas-phase dissociation pathways of multiply charged peptide clusters.

Numerous studies of cluster formation and dissociation have been conducted to determine properties of matter in the transition from the condensed phase to the gas phase using materials as diverse as atomic nuclei, noble gases, metal clusters, and amino acids. Here, electrospray ionization is used to extend the study of cluster dissociation to peptides including leucine enkephalin with 7-19 monomer units and 2-5 protons, and somatostatin with 5 monomer units and 4 protons under conditions where its intramolecular disulfide bond is either oxidized or reduced. Evaporation of neutral monomers and charge separation by cluster fission are the competing dissociation pathways of both peptides.

Characterization of a novel gastropod toxin (6-bromo-2-mercaptotryptamine) that inhibits shaker K channel activity.

A novel potassium channel antagonist has been purified from the defensive mucus secreted by Calliostoma canaliculatum, a marine snail found in the temperate coastal waters of the western Pacific. The toxin is expelled from the hypobranchial gland as part of a defensive response and is contained within a viscous matrix that minimizes dilution and degradation. The active compound was isolated by multistage microbore HPLC separations followed by bioactivity assays.

Origin of asymmetric charge partitioning in the dissociation of gas-phase protein homodimers.

The origin of asymmetric charge and mass partitioning observed for gas-phase dissociation of multiply charged macromolecular complexes has been hotly debated. These experiments hold the potential to provide detailed information about the interactions between the macromolecules within the complex. Here, this unusual phenomenon of asymmetric charge partitioning is investigated for several protein homodimers.