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Biomedical subjects

E Hartmann

Publications and source records attributed to E Hartmann.

At least 109 records · Page 6Linked to original sources
PubMed1993

Syllabic timing in dysarthria.

A new, intensity-based method of measuring syllable duration was used to assess syllabic timing in 75 patients with dysarthria of predominantly traumatic and cerebro-vascular origin and in 30 normal subjects. The applied speech tasks included repetitions of sentences containing chains of plosive-vowel-syllables. The logarithm of the duration of the syllable carrying sentence accent proved to be particularly highly correlated with perceived speech rate. Among the potential sources of temporal variability, segmental influences and the influence of sentence stress were examined. Further, the between-sentence variation of syllable duration was assessed. The resulting measures of variability were correlated with the severity of dysarthric impairment. A strengthening of normal effects was found in the consonant-related variation, whereas intrinsic vowel effects and the influence of sentence stress were largely reduced. These results are discussed from the viewpoint of timing theories in speech and limb motor control. They are considered to provide a valuable background against which the speech impairments of specific neurologic groups can be tested.

Adolescent↗
PubMed1993

Sec61p is adjacent to nascent type I and type II signal-anchor proteins during their membrane insertion.

We have identified membrane components which are adjacent to type I and type II signal-anchor proteins during their insertion into the membrane of the ER. Using two different cross-linking approaches a 37-38-kD nonglycosylated protein, previously identified as P37 (High, S., D. Görlich, M. Wiedmann, T. A. Rapoport, and B. Dobberstein. 1991. J. Cell Biol. 113:35-44), was found adjacent to all the membrane inserted nascent chains used in this study. On the basis of immunoprecipitation, this ER protein was shown to be identical to the recently identified mammalian Sec61 protein. Thus, Sec61p is the principal cross-linking partner of both type I and type II signal-anchor proteins during their membrane insertion (this work), and of secretory proteins during their translocation (Görlich, D., S. Prehn, E. Hartmann, K.-U. Kalies, and T. A. Rapoport. 1992. Cell. 71:489-503). We propose that membrane proteins of both orientations, and secretory proteins employ the same ER translocation sites, and that Sec61p is a core component of these sites.

Base Sequence↗
PubMed1993

Proposed pathway for biosynthesis of the S-layer glycoprotein of Bacillus alvei.

The outer surface of the murein sacculus of the eubacterium Bacillus alvei is covered by a surface layer (S-layer) glycoprotein. The glycan chain of this S-layer glycoprotein consists of trisaccharide repeating units with ManNAc, Gal, and Glc as constituents. From cell extracts of B. alvei, nucleotide-activated derivatives of ManNAc, Gal, Glc, and GlcNAc were isolated. Furthermore, GDP- and dolichyl-activated oligosaccharides were obtained. On the basis of the isolated putative glycoprotein precursors, a pathway for the biosynthesis of the oligosaccharide chain is proposed.

Bacillus↗
PubMed1993

[Munich Intelligibility Profile. Studies of reliability and validity].

The 'Münchner Verständlichkeitsprofil (MVP)' (Munich Intelligibility Profile) is a PC-based method for assessment of the intelligibility of dysarthric speakers. Analyses of its reliability and validity were based on a total of 101 patients and 16 normal speakers as well as a group of 45 listeners. The reliability of the overall MVP score was determined using non-parametric analyses of variance and between-listener correlations. Retest reliability was measured for a subgroup of 5 listeners. Test validity was analyzed by correlating MVP scores with three external criteria (expert ratings, listeners' ratings, transcripts). Further, relevant aspects of the test construction were tested empirically. Finally, regression analyses were carried out in order to demonstrate that different MVP lists are equivalent in predicting transcription-based intelligibility scores.

Adolescent↗
PubMed1992

A mammalian homolog of SEC61p and SECYp is associated with ribosomes and nascent polypeptides during translocation.

SEC61p is essential for protein translocation across the endoplasmic reticulum membrane of S. cerevisiae. We have found a mammalian homolog that shows more than 50% sequence identity with the yeast protein. Moreover, several regions of SEC61p have significant similarities with corresponding ones of SecYp of bacteria, indicating a strong evolutionary conservation of the mechanism of protein translocation. Mammalian Sec61p, like the yeast protein, is located in the immediate vicinity of nascent polypeptides during their membrane passage. It is tightly associated with membrane-bound ribosomes, suggesting that the nascent chain passes directly from the ribosome into a protein-conducting channel. These results define Sec61p as a ubiquitous key component of the protein translocation apparatus.

Amino Acid Sequence↗
PubMed1992

A protein of the endoplasmic reticulum involved early in polypeptide translocation.

To identify components of the mammalian endoplasmic reticulum involved in the translocation of secretory proteins, crosslinking and reconstitution methods were combined. A multispanning abundant membrane glycoprotein was found which is in proximity to nascent chains early in translocation. In reconstituted proteoliposomes, this protein is stimulatory or required for the translocation of secretory proteins.

Amino Acid Sequence↗
PubMed1992

[Diagnosis of dysarthria with the "Munich Intelligibility Profile"--construction of the procedure and its use].

No German-based methods for reliable assessment of the intelligibility of dysarthric speech have yet been described. The techniques usually applied in clinical diagnostics take no account of the various factors influencing the understanding of spoken language. They also fail to differentiate between individual patterns of impaired intelligibility. The intelligibility profile presented here controls for the most relevant influencing factors and allows us to discern therapeutically relevant patterns of disturbed intelligibility. The principles of its construction and some applications are presented.

Cerebellar Diseases↗
PubMed1991

Effects of day care and maternal teaching on child educability.

Two groups of matched mother-child pairs, a day care sample (N = 38) and a home reared sample (N = 38) participated in a study testing mothers for degree of decentred teaching and children for degree of decentred educability. The children were seven years old. Mother and child were tested in separate settings, thus preventing interdependency among scores. The study used a matched-pair design with control of five background variables; age of the child, mother's educational level, mother's occupational status, family SES level, and type of family. The results showed strong positive effects of both day care experience and maternal teaching on child educability. Day care experience improved the educability of children independent of the mother's teaching strategy and gender of the child.

Achievement↗
PubMed1991

Nucleotide-activated oligosaccharides are intermediates of the cell wall polysaccharide of Methanosarcina barkeri.

The cell wall of Methanosarcina barkeri consists of a heteropolysaccharide (methanochondroitin), which resembles the eukaryotic chondroitin. From cell extracts of Methanosarcina barkeri four uridine diphosphate and one undecaprenyl pyrophosphate-activated intermediate(s) of the methanochondroitin were isolated. In contrast to the known biosynthetic pathways of polysaccharides from other prokaryotes and eukaryotes, nucleotide activated oligosaccharide precursors are involved in the case of the methanochondroitin. Usually, oligosaccharides are synthesized at the lipid stage.

Amino Sugars↗
PubMed1990

Isolation of nucleotide activated amino acid and peptide precursors of the pseudomurein of Methanobacterium thermoautotrophicum.

The following putative precursors of the pseudomurein were isolated from trichloroacetic acid extracts of Methanobacterium thermoautotrophicum: a uridine diphosphate activated derivative of glutamic acid and the uridine diphosphate activated peptides (see text). The activated glutamic acid residue and the three activated pepetides lack the glycan components N-acetylglucosamine and N-acetyltalosaminuronic acid present in the intact pseudomurein. In this case uridine diphosphate should be directly linked to the amino group of a glutamic acid residue, which represents a new mode of amino acid and peptide activation.

Amino Acid Sequence↗
PubMed1990

Structure and biosynthesis of the signal-sequence receptor.

The signal-sequence receptor (SSR) has previously been shown to be a component of the environment which nascent polypeptides meet on passage through the endoplasmic reticulum (ER) membrane. We report here on the primary structure of the SSR as deduced from cDNA clones and from direct protein sequencing. The glycoprotein is synthesized with a cleavable amino-terminal signal sequence and contains only one classical membrane-spanning segment. Its insertion into the ER membrane during biosynthesis depends on the function of the signal-recognition particle. SSR shows a remarkable charge distribution with the amino terminus being highly negatively charged, and the cytoplasmic carboxyl terminus positively charged. The SSR can be phosphorylated in its cytoplasmic tail both in intact cells and in a cell-free system, suggesting a regulation of its function. The localization of the protein in the ER membrane was confirmed by immunofluorescence microscopy.

Amino Acid Sequence↗
PubMed1990

Isolation of lipid activated pseudomurein precursors from Methanobacterium thermoautotrophicum.

From cell extracts of the pseudomurein possessing methanogen Methanobacterium thermoautotrophicum two putative pseudomurein precursors were isolated and characterized: (1) an undecaprenyl pyrophosphate activated disaccharide pentapeptide composed of N-acetylglucosamine, N-acetyltalosaminuronic acid, alanine, glutamic acid and lysine in a molar ratio of 1:1:2:2:1 and (2) the corresponding undecaprenyl pyrophosphate activated tetrapeptide lacking one alanine residue. The isolation of these precursors show that the biosynthesis of the eubacterial murein and the methanobacterial pseudomurein differs not only in the cytoplasmic step, as recently described, but also in the lipid stage.

Amino Acid Sequence↗
PubMed1990

Comparison of the biosynthesis of the methanobacterial pseudomurein and the eubacterial murein.

From cell extracts of the archaebacterium Methanobacterium thermoautotrophicum 11 putative precursors of the pseudomurein were isolated and characterized. On the basis of the isolated intermediates, a biosynthetic pathway of the pseudomurein is proposed. Compared to the eubacterial murein the biosynthetic stages follow different pathways as indicated by the occurrence of a nucleotide-activated disaccharide and nucleotide-activated peptides.

Amino Acid Sequence↗
PubMed1990

Microtubule distribution in gravitropic protonemata of the moss Ceratodon.

Tip cells of dark-grown protonemata of the moss Ceratodon purpureus are negatively gravitropic (grow upward). They possess a unique longitudinal zonation: (1) a tip group of amylochloroplasts in the apical dome, (2) a plastid-free zone, (3) a zone of significant plastid sedimentation, and (4) a zone of mostly non-sedimenting plastids. Immunofluorescence of vertical cells showed microtubules distributed throughout the cytoplasm in a mostly axial orientation extending through all zones. Optical sectioning revealed a close spatial association between microtubules and plastids. A majority (two thirds) of protonemata gravistimulated for > 20 min had a higher density of microtubules near the lower flank compared to the upper flank in the plastid-free zone. This apparent enrichment of microtubules occurred just proximal to sedimented plastids and near the part of the tip that presumably elongates more to produce curvature. Fewer than 5% of gravistimulated protonemata had an enrichment in microtubules near the upper flank, whereas 14% of vertical protonemata were enriched near one of the side walls. Oryzalin and amiprophos-methyl (APM) disrupted microtubules, gravitropism, and normal tip growth and zonation, but did not prevent plastid sedimentation. We hypothesize that a microtubule redistribution plays a role in gravitropism in this protonema. This appears to be the first report of an effect of gravity on microtubule distribution in plants.

Cell Compartmentation↗
PubMed1990

A novel pathway for secretory proteins?

In eukaryotes, most proteins which are transported to the extracellular space, into mitochondria or into chloroplasts are synthesized as precursor polypeptides containing cleavable N-terminal signal or targeting sequences. We have searched the literature for proteins that are exported from the cytosol without being proteolytically processed. Some of these proteins contain uncleaved signal or targeting sequences. However, among secretory proteins there is a class that does not possess hydrophobic signal sequences and appears to leave the cell by a secretory pathway clearly distinct from the classical route through the endoplasmic reticulum and Golgi apparatus.

Acylation↗
PubMed1990

The signal sequence receptor has a second subunit and is part of a translocation complex in the endoplasmic reticulum as probed by bifunctional reagents.

Bifunctional cross-linking reagents were used to probe the protein environment in the ER membrane of the signal sequence receptor (SSR), a 24-kD integral membrane glycoprotein (Wiedmann, M., T. V. Kurzchalia, E. Hartmann, and T. A. Rapoport. 1987. Nature [Lond.]. 328:830-833). The proximity of several polypeptides was demonstrated. A 22-kD glycoprotein was identified tightly bound to the 34-kD SSR even after membrane solubilization. The 34-kD polypeptide, now termed alpha SSR, and the 22-kD polypeptide, the beta SSR, represent a heterodimer. We report on the sequence of the beta SSR, its membrane topology, and on the mechanism of its integration into the membrane. Cross-linking also produced dimers of the alpha-subunit of the SSR indicating that oligomers of the SSR exist in the ER membrane. Various bifunctional cross-linking reagents were used to study the relation to ER membrane proteins of nascent chains of preprolactin and beta-lactamase at different stages of their translocation through the membrane. The predominant cross-linked products obtained in high yields contained the alpha SSR, indicating in conjunction with previous results that it is a major membrane protein in the neighborhood of translocating nascent chains of secretory proteins. The results support the existence of a translocon, a translocation complex involving the SSR, which constitutes the specific site of protein translocation across the ER membrane.

Amino Acid Sequence↗