Biomedical subjects

M S Weiss

Publications and source records attributed to M S Weiss.

11 recordsLinked to original sources

PubMed1992

Structure of porin refined at 1.8 A resolution.

The crystal structure of porin from Rhodobacter capsulatus has been refined using the simulated annealing method. The final model consists of all 301 amino acid residues well obeying standard geometry, three calcium ions, 274 solvent molecules, three detergent molecules and one unknown ligand modeled as a detergent molecule. The final crystallographic R-factor is 18.6% based on 42,851 independent reflections in the resolution range 10 to 1.8 A. The model is described in detail.

Amino Acid Sequence↗

PubMed1991

Molecular architecture and electrostatic properties of a bacterial porin.

The integral membrane protein porin from Rhodobacter capsulatus consists of three tightly associated 16-stranded beta barrels that give rise to three distinct diffusion channels for small solutes through the outer membrane. The x-ray structure of this porin has revealed details of its shape, the residue distributions within the pore and at the membrane-facing surface, and the location of calcium sites. The electrostatic potential has been calculated and related to function. Moreover, potential calculations were found to predict the Ca2+ sites.

Bacterial Outer Membrane Proteins↗

PubMed1991

Prediction of the general structure of OmpF and PhoE from the sequence and structure of porin from Rhodobacter capsulatus. Orientation of porin in the membrane.

By comparing the hydrophilicity profiles and sequences of porin from Rhodobacter capsulatus with those of OmpF and PhoE from Escherichia coli, a set of insertions and deletions for alignment of the sequences has been deduced. With this alignment a similar folding of OmpF and PhoE has been predicted as found by X-ray structure analysis of porin from Rhodobacter capsulates. Furthermore, the orientation of the porin trimer in the outer membrane was inferred from topological data on PhoE. According to this result a single channel of approx. 30 A diameter starts at the outer surface. Near the middle of the outer membrane bilayer this channel branches out into three separate channels, each running within a single porin monomer to the periplasmic surface.

Amino Acid Sequence↗

PubMed1991

The structure of porin from Rhodobacter capsulatus at 1.8 A resolution.

The structure of the porin from Rhodobacter capsulatus was determined at a resolution of 1.8 A. The analysis started from a closely related crystal structure that had been solved at a medium resolution of 3 A using multiple isomorphous replacement and solvent flattening. The new structure contains the complete sequence of 301 amino acid residues. Refinement of the model is under way; the present R-factor is 22% with good geometry. Except for the lengths of several loops, the resulting chain fold corresponds to the medium resolution model. The membrane channel is lined by a large number of ionogenic side chains with characteristic segregation of differently charged groups.

Amino Acids↗

PubMed1991

Crystals of an integral membrane protein diffracting to 1.8 A resolution.

A new crystal form of porin from Rhodobacter capsulatus has been obtained. The crystals are rhombohedral, space group R3, with hexagonal axes a = b = 92.3 A, c = 146.2 A. They contain one monomer in the asymmetric unit and diffract to a resolution of at least 1.8 A.

Bacterial Outer Membrane Proteins↗

PubMed1991

A common channel-forming motif in evolutionarily distant porins.

Four new crystal packings of Escherichia coli porins are presented (phosphoporin, maltoporin, and two crystal forms of matrix porin). These were determined by molecular replacement methods using a polyalanine trial model acquired from the refined coordinates of porin from Rhodobacter capsulatus. The successful molecular replacement shows that the dominant motif found in R. capsulatus porin (a 16-stranded antiparallel beta-barrel) also applies to the E. coli porins, despite the lack of significant amino acid sequence homology. A 30 degrees-40 degrees tilt of the beta-strands with respect to the membrane normal was derived from the intensity distributions in the X-ray diffraction patterns for each porin studied, stressing their similarity. In view of the evolutionary distance between enteric and photosynthetic bacteria, the antiparallel beta-barrel may have significance as a basic structural motif for the formation of bacterial membrane channel structures.

Bacterial Outer Membrane Proteins↗

PubMed1990

The three-dimensional structure of porin from Rhodobacter capsulatus at 3 A resolution.

The crystal structure of porin from Rhodobacter capsulatus strain 37b4 has been solved at 3.0 A (1 A = 0.1 nm) resolution by multiple isomorphous replacement and solvent-flattening. The three pores of the trimer are well defined in the electron density map. Each pore consists of a 16-stranded beta-barrel which traverses the membrane as a tube. Near its center the tube is narrowed by chain segments protruding from the inner wall of the barrel that form an eye-let with an irregular cross-section of about 6 A by 10 A. The eye-let has an axial length of about 10 A; it defines the exclusion limit for diffusing particles.

Bacterial Outer Membrane Proteins↗

PubMed1979

Acoustical and perceptual characteristics of speech produced with an electronic artificial larynx.

Five normal-speaking adult males were taught to produce speech using an electrolarynx. Speech phoneme intelligibility was measured in a closed-set word discrimination test and through phonetic transcriptions of the spoken materials. Mean percentages of correct identification for the five talkers were 90% and 57% for the word-identification test and phonetic transcription, respectively. An analysis of perceptual confusions revealed that errors were most frequently associated with the voicing feature and that few manner or place of articulation errors occurred. Over the range of variables observed, the intensity of both the speech and the noise radiating directly from the electrolarynx, the spectrum of the radiated noise and speaking rate were not found to be determinants of intelligibility.

Acoustics↗

PubMed1979

Masking of filtered noise bursts by synthetic vowels.

The present investigation assessed the simultaneous and temporal masking produced by computer-generated synthetic vowels. The durations (100 and 200 ms) of each of four vowel-like maskers were employed. The masker was presented at 70 dB SPL. The probe signals were three filtered noise bursts whose spectral distributions corresponded to regions of high spectral energy in three English stop consonants. Quiet and masked thresholds were determined using the method of adjustment. Data are reported for two experienced listeners who participated in all the listening conditions. The results were generally in accord with the results of masking experiments using nonspeech signals in that both the frequency specificity of masking and temporal masking effects were demonstrated.

Computers↗

PubMed1979

Post-void residual alerting device.

A simple, inexpensive device is described which alerts nursing staff upon spontaneous voiding by a patient with spinal cord injury. This facilitates measurement of the post-void residual urine volume which is useful in the management of neurogenic bladder.

Humans↗

PubMed1978

Toxicity of D-penicillamine in rheumatoid arthritis. A report of 63 patients including two with aplastic anemia and one with the nephrotic syndrome.

To assess toxicity of D-penicillamine a retrospective chart review was performed on 63 patients with rheumatoid arthritis receiving penicillamine. These patients had a total of 83 courses of therapy. The mean age of patients was 52 years and the mean duration of disease was 10.07 years. Laboratory data showed an increase in hematocrit values from 36 per cent to 40 per cent and a decrease in the erythrocyte sedimentation rate from an average of 50 to 29 mm/hour. The platelet count also decreased with treatment from 394,000 to 267,000/mm3. The over-all complication rate was 53 per cent. Life-threatening complications occurred in two patients including one case of aplastic anemia and one case of nephrotic syndrome. One additional patient was referred with aplastic anemia. Minor complications include rash in 18 per cent, loss of taste in 6 per cent, dyspepsia in 11 per cent, oral ulceration in 7 per cent and proteinuria of less than 3 g/day in 8 per cent. In summary, 53 per cent of the courses of penicillamine were associated with toxicity including one episode of aplastic anemia and one case of nephrotic syndrome. Therapy was stopped due to complications in 39 per cent of the patients in this series.

Adult↗