Search PubMed⌕ Search

Biomedical subjects

M R Schroeder

Publications and source records attributed to M R Schroeder.

At least 19 recordsLinked to original sources
PubMed1993

Crystallization and preliminary X-ray diffraction studies of recombinant barley lectin and pro-barley lectin.

Barley lectin (BL) and its precursor form (proBL), synthesized and over-expressed in Escherichia coli, have been crystallized under conditions identical to those used for the closely related lectin wheat germ agglutinin. These lectins are members of the Gramineae family and possess a unique disulfide-rich domain structure. The pro-lectin polypeptides are extended by 15 amino acid residues at the carboxy terminus. This pro-peptide, which is proteolytically removed as the mature lectin is deposited in the vacuoles, is thought to function as a targeting signal for molecular sorting. Crystals of BL and proBL are well ordered and belong to space groups C222(1) and P2(1)2(1)2(1). The unit cell dimensions for BL and proBL are a = 51.9 A, b = 73.7 A, c = 89.3 A (one monomer per asymmetric unit), and a = 45.2 A, b = 70.5 A, c = 111.6 A (two monomers per asymmetric unit), respectively. Diffraction patterns on precession photographs of BL crystals are closely similar to those of mature wheat germ agglutinin crystals, suggesting similar crystal packing and correct conformation of this recombinant protein in terms of the four structural domains and 16 disulfide bridges.

Crystallization↗
PubMed1993

Colocalization of barley lectin and sporamin in vacuoles of transgenic tobacco plants.

Various targeting motifs have been identified for plant proteins delivered to the vacuole. For barley (Hordeum vulgare) lectin, a typical Gramineae lectin and defense-related protein, the vacuolar information is contained in a carboxyl-terminal propeptide. In contrast, the vacuolar targeting information of sporamin, a storage protein from the tuberous roots of the sweet potato (Ipomoea batatas), is encoded in an amino-terminal propeptide. Both proteins were expressed simultaneously in transgenic tobacco plants to enable analysis of their posttranslational processing and subcellular localization by pulse-chase labeling and electron-microscopic immunocytochemical methods. The pulse-chase experiments demonstrated that processing and delivery to the vacuole are not impaired by the simultaneous expression of barley lectin and sporamin. Both proteins were targeted quantitatively to the vacuole, indicating that the carboxyl-terminal and amino-terminal propeptides are equally recognized by the vacuolar protein-sorting machinery. Double-labeling experiments showed that barley lectin and sporamin accumulate in the same vacuole of transgenic tobacco (Nicotiana tabacum) leaf and root cells.

Amino Acid Sequence↗
PubMed1993

Determination of the functional elements within the vacuolar targeting signal of barley lectin.

We have previously demonstrated that the carboxyl-terminal propeptide of barley lectin is both necessary and sufficient for protein sorting to the plant vacuole. Specific mutations were constructed to determine which amino acid residues or secondary structural determinants of the carboxyl-terminal propeptide affect proper protein sorting. We have found that no consensus sequence or common structural determinants are required for proper sorting of barley lectin to the vacuole. However, our analysis demonstrated the importance of hydrophobic residues in vacuolar targeting. In addition, at least three exposed amino acid residues are necessary for efficient sorting. Sorting was disrupted by the addition of two glycine residues at the carboxyl-terminal end of the targeting signal or by the translocation of the glycan to the carboxy terminus of the propeptide. These results suggest that some components of the sorting apparatus interact with the carboxy terminus of the propeptide.

Amino Acid Sequence↗
PubMed1992

Isolation and characterization of pro-barley lectin expressed in Escherichia coli.

Lectins are a class of proteins with specific carbohydrate-binding properties found in a wide variety of plants and animals. Gramineae lectins are presumably defense-related proteins in plants that exert their effect by binding to N-acetylglucosamine. Barley lectin is a vacuolar protein synthesized with an amino-terminal signal sequence for entering the secretory pathway and a carboxyl-terminal propeptide necessary for proper targeting to the vacuole. To analyze the three-dimensional structure of barley lectin with the carboxyl-terminal extension and to investigate whether the conversion of the prolectin into the mature molecule leads to a conformational change, the precursor and the mature forms of barley lectin were expressed in Escherichia coli. Both proteins accumulated in denatured form in inclusion bodies were solubilized in 8 M urea and renatured in a redox buffer system. Active pro- and mature barley lectins were purified to homogeneity by affinity chromatography.

Acetylglucosamine↗
PubMed1986

Flat-spectrum speech.

Flat-spectrum stimuli, consisting of many equal-amplitude harmonics, produce timbre sensations that can depend strongly on the phase angles of the individual harmonics. For fundamental frequencies in the human pitch range, many realizable timbres have vowel-like perceptual qualities. This observation suggests the possibility of constructing intelligible voiced speech signals that have flat-amplitude spectra. This paper describes a successful experiment of creating several different diphthongs by judicious choice of the phase angles of a flat-spectrum waveform. A possible explanation of the observed vowel timbres lies in the dependence of the short-time amplitude spectra on phase changes.

Acoustic Stimulation↗
PubMed1986

Auditory paradox based on fractal waveform.

The synthesis of certain paradoxical acoustic waveforms is described that will sound lower when reproduced at higher speeds (and vice versa). Specifically, one such waveform, when recorded on magnetic tape, will sound a semitone lower (rather than an octave higher) when played back at twice the tape speed. The connection with fractal objects in geometry is illustrated.

Humans↗
PubMed1986

Phase effects in masking related to dispersion in the inner ear.

Phase effects in masking experiments using multitone maskers are usually associated with strong variations in the masker envelope. In this article, psychoacoustic experiments with such maskers that lead to phase-dependent threshold variations of up to 20 dB, although the phase transformation leaves the envelope unchanged, are described. However, after filtering the maskers with a realistic basilar membrane model, the envelopes are different owing to the models phase-dispersive properties. Comparison of model outputs with the experimental results reveals a strong correlation between the two for a wide range of parameters, provided one makes the additional assumption that the ear has a minimum integration time of a few milliseconds.

Auditory Threshold↗
PubMed1979

Acoustic measurements of articulator motions.

Methods for estimating articulatory data from acoustic measurements are reviewed. First, relations between the vocal-tract area function and formant or impedance data are pointed out. Then the possibility of determining a (discretized) area function from the speech signal itself is considered. Finally, we look at the estimation of certain articulatory parameters rather than the area function. By using a regression method, such parameters can even be estimated independently of any vocal-tract model. Results for real-speech data are given.

Humans↗
PubMed1978

Linear prediction analysis of speech based on a pole-zero representation.

Speech analysis and synthesis by linear prediction is based on the assumption that the short-time spectral envelope of speech can be represented by a number of poles. An all-pole representation does not provide an accurate description of speech spectra, particularly for nasals and nasalized sounds. This paper presents a method for characterizing speech in terms of the parameters of a pole-zero model. In this method, an impulse response representing the composite filtering action of the glottal wave, the vocal tract, the radiation, and the speech recording system is first constructed from the speech signal. This impulse response is obtained by performing several stages of all-pole LPC analysis. The pole-zero parameters are determined from the impulse response by solving a set of simultaneous linear equations. The method, being noniterative, is very suitable for automatic analysis of speech. The method has been applied to real speech data and the results show that the speech spectra derived from the pole-zero model agree very closely with the actual spectra derived by direct Fourier analysis.

Acoustics↗