Lessons in Using Vibrotactile Feedback to Guide Fast Arm Motions

We present and evaluate an arm-motion guidance system that uses magnetic tracking sensors and low cost vibrotactile actuators. The system measures the movement of the user’s arm and provides vibration feedback at the wrist and elbow when they stray from the desired motion. An initial study was conducted to investigate whether adding tactile feedback to visual feedback reduces motion errors when a user is learning a new arm trajectory. Although subjects preferred it, we found that the addition of tactile feedback did not affect motion tracking performance. We also found no strong preference or performance differences between attractive and repulsive tactile feedback. Some factors that may have influenced these results include the speed and the complexity of the tested motions, the type of tactile actuators and drive signals used, and inconsistencies in joint angle estimation due to Euler angle gimbal lock. We discuss insights from this analysis and provide suggestions for future systems and studies in tactile motion guidance

Neuropeptidomic Components Generated by Proteomic Functions in Secretory Vesicles for Cell–Cell Communication

Diverse neuropeptides participate in cell–cell communication to coordinate neuronal and endocrine regulation of physiological processes in health and disease. Neuropeptides are short peptides ranging in length from ~3 to 40 amino acid residues that are involved in biological functions of pain, stress, obesity, hypertension, mental disorders, cancer, and numerous health conditions. The unique neuropeptide sequences define their specific biological actions. Significantly, this review article discusses how the neuropeptide field is at the crest of expanding knowledge gained from mass-spectrometry-based neuropeptidomic studies, combined with proteomic analyses for understanding the biosynthesis of neuropeptidomes. The ongoing expansion in neuropeptide diversity lies in the unbiased and global mass-spectrometry-based approaches for identification and quantitation of peptides. Current mass spectrometry technology allows definition of neuropeptide amino acid sequence structures, profiling of multiple neuropeptides in normal and disease conditions, and quantitative peptide measures in biomarker applications to monitor therapeutic drug efficacies. Complementary proteomic studies of neuropeptide secretory vesicles provide valuable insight into the protein processes utilized for neuropeptide production, storage, and secretion. Furthermore, ongoing research in developing new computational tools will facilitate advancements in mass-spectrometry-based identification of small peptides. Knowledge of the entire repertoire of neuropeptides that regulate physiological systems will provide novel insight into regulatory mechanisms in health, disease, and therapeutics

Enhancing MALDI Time-Of-Flight Mass Spectrometer Performance through Spectrum Averaging

<div><p>Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometers are simple and robust mass spectrometers used for analysis of biologically relevant molecules in diverse fields including pathogen identification, imaging mass spectrometry, and natural products chemistry. Despite high nominal resolution and accuracy, we have observed significant variability where 30–50% of individual replicate measurements have errors in excess of 5 parts-per-million, even when using 5-point internal calibration. Increasing the number of laser shots for each spectrum did not resolve this observed variability. What is responsible for our observed variation? Using a modern MALDI-TOF/TOF instrument, we evaluated contributions to variability. Our data suggest a major component of variability is binning of the raw flight time data by the electronics and clock speed of the analog-to-digital (AD) detection system, which requires interpolation by automated peak fitting algorithms and impacts both calibration and the observed mass spectrum. Importantly, the variation observed is predominantly normal in distribution, which implies multiple components contribute to the observed variation and suggests a method to mitigate this variability through spectrum averaging. Restarting the acquisition impacts each spectrum within the electronic error of the AD detector system and defines a new calibration function. Therefore, averaging multiple independent spectra and not a larger number of laser shots leverages this inherent binning error to mitigate variability in accurate MALDI-TOF mass measurements.</p></div

Identification of tubulin peptides by ProFound peptide mass fingerprinting using immunoprecipitation experiments and averaged MALDI-TOF/TOF data.

<p>Tubulin was immunoprecipitated from HEK293 cell lysate using a rabbit polyclonal antibody and Protein A/G Dynabeads. After isolation, all eluted proteins were reduced and alkylated, digested with trypsin, and analyzed on an ABI 4800 MALDI-TOF/TOF mass spectrometer. Multiple individual spectra were acquired with internal calibration and between 10 and 23 individual measurements for each peptide were used for calculating the average observed masses for each peptide. Mass Tolerance is in parts-per-million (ppm), Peptide Set defines the peptides included for search and Search Mass Range/pI Range are input parameters for Profound. Top Protein ID and Expectation Value were calculated within ProFound from the mass spectrometry data using the IPI Human database (2010-02-01).</p><p>Identification of tubulin peptides by ProFound peptide mass fingerprinting using immunoprecipitation experiments and averaged MALDI-TOF/TOF data.</p

Evidence for discontinuous binning of MALDI-TOF mass spectrometry data for Des-Arg(9) Bradykinin (A), Angiotensin 1 (B), and ACTH 1–17 (C).

<p>Representative monoisotopic peaks for Des-Arg(9) Bradykinin (MH+ = 904.4676), Angiotensin 1 (MH+ = 1296.6848) and ACTH 1–17 (MH+ = 2093.0862) are enlarged to demonstrate the discontinuous sampling points (or bins) within the MALDI-TOF data. The red vertical lines are fitted to the bins evident in the observed peak shapes. The spacing of bins in mass units is larger for higher mass ions and can be accurately calculated by relationship between flight times and the ratio of masses of the molecular ions according to the equation Δt₂/Δt₁ = (M₂/M₁)^1/2. This calculation is simplistic, but accurately relates the bin spacing for different mass ions to 5 decimal places, thus suggesting that binning of data in the MALDI-TOF instrument is related to the measurements of ion flight times.</p

Absolute values for mean, maximum and minimum errors observed for peptides from a standard protein trypsin digestion demonstrate higher variability in the more inaccurate data.

<p>Measured errors were converted to absolute values to evaluate the dispersion of data measurements and plotted according to peptide. The uneven distribution of maximum and minimum errors is expected because of zero as a lower bound for minimum error. Note, absolute value transformation of the data eliminates negative values and the mean errors reported here are higher than the mean reported for the observed peptide masses, which contain both positive and negative errors.</p

Beta-Tubulin identification and limitations of peptide mass fingerprinting.

<p>The identification of tubulin from peptide mass fingerprinting matches with LC-MS/MS data for the majority of peptides. However, assignment for the 1249.585 and 1696.805 peptides were inaccurate. The 1249.585 peak was not assigned in the MALDI-TOF data. The observed mass of 1696.805 and data in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0120932#pone.0120932.t003" target="_blank">Table 3</a> are from ProFound and assigned to peptide sequence ALTVSELTQQMFDSK (data denoted with an asterisk *). Peptide fragmentation data using LC-MS/MS suggests this assignment is incorrect and that the correct sequence is NSSYFVEWIPNNVK with deamidation at the amino-terminus yielding the sequence DSSYFVEWIPNNVK (MH+ = 1697.817 expected, 1697.813 observed, −2.4 ppm error).</p><p>Beta-Tubulin identification and limitations of peptide mass fingerprinting.</p