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Biomedical subjects

E Wallin

Publications and source records attributed to E Wallin.

At least 19 recordsLinked to original sources
PubMed1999

Topology, subcellular localization, and sequence diversity of the Mlo family in plants.

Barley Mlo defines the founder of a novel class of plant integral membrane proteins. Lack of the wild type protein leads to broad spectrum disease resistance against the pathogenic powdery mildew fungus and deregulated leaf cell death. Scanning N-glycosylation mutagenesis and Mlo-Lep fusion proteins demonstrated that Mlo is membrane-anchored by 7 transmembrane (TM) helices such that the N terminus is located extracellularly and the C terminus intracellularly. Fractionation of leaf cells and immunoblotting localized the protein to the plant plasma membrane. A genome-wide search for Mlo sequence-related genes in Arabidopsis thaliana revealed approximately 35 family members, the only abundant gene family encoding 7 TM proteins in higher plants. The sequence variability of Mlo family members within a single species, their topology and subcellular localization are reminiscent of the most abundant class of metazoan 7 TM receptors, the G-protein-coupled receptors.

Amino Acids↗
PubMed1999

Divergent evolution of membrane protein topology: the Escherichia coli RnfA and RnfE homologues.

Although the molecular evolution of protein tertiary structure and enzymatic activity has been studied for decades, little attention has been paid to the evolution of membrane protein topology. Here, we show that two closely related polytopic inner membrane proteins from Escherichia coli have evolved opposite orientations in the membrane, which apparently has been achieved by the selective redistribution of positively charged amino acids between the polar segments flanking the transmembrane stretches. This example of divergent evolution of membrane protein topology suggests that a complete inversion of membrane topology is possible with relatively few mutational changes even for proteins with multiple transmembrane segments.

Alkaline Phosphatase↗
PubMed1998

Stop-transfer function of pseudo-random amino acid segments during translocation across prokaryotic and eukaryotic membranes.

We have measured the efficiency of stop-transfer function for a set of pseudo-random, 18-residue amino acid segments, both in Escherichia coli and in mammalian microsomes. In general, stop-transfer function correlates well with the mean hydrophobicity of the segment, though exceptions exist. Kinetic studies suggest that polar segments are rapidly translocated through the E. coli inner membrane and that strongly hydrophobic segments become permanently anchored, while sequences with an intermediate mean hydrophobicity become partly trapped in a transmembrane disposition for a considerable time before being released to the periplasm or degraded.

Alkaline Phosphatase↗
PubMed1998

Genome-wide analysis of integral membrane proteins from eubacterial, archaean, and eukaryotic organisms.

We have carried out detailed statistical analyses of integral membrane proteins of the helix-bundle class from eubacterial, archaean, and eukaryotic organisms for which genome-wide sequence data are available. Twenty to 30% of all ORFs are predicted to encode membrane proteins, with the larger genomes containing a higher fraction than the smaller ones. Although there is a general tendency that proteins with a smaller number of transmembrane segments are more prevalent than those with many, uni-cellular organisms appear to prefer proteins with 6 and 12 transmembrane segments, whereas Caenorhabditis elegans and Homo sapiens have a slight preference for proteins with seven transmembrane segments. In all organisms, there is a tendency that membrane proteins either have many transmembrane segments with short connecting loops or few transmembrane segments with large extra-membraneous domains. Membrane proteins from all organisms studied, except possibly the archaeon Methanococcus jannaschii, follow the so-called "positive-inside" rule; i.e., they tend to have a higher frequency of positively charged residues in cytoplasmic than in extra-cytoplasmic segments.

Animals↗
PubMed1998

Architecture of beta-barrel membrane proteins: analysis of trimeric porins.

We have analyzed the known three-dimensional structures of trimeric porins from bacterial outer membranes. The distribution of surface-exposed residues in a direction perpendicular to the membrane is similar to that in helical membrane proteins, with aliphatic residues concentrated in the central 20 A of the bilayer. Outside these residues is a layer of aromatic residues, followed by polar and charged residues. Residues in the trimer interface are more conserved than residues not in the interface. By comparing the interface and noninterface residues, an interface preference scale has been derived that may be used as a basis for predicting interface surfaces in monomer models.

Bacterial Proteins↗
PubMed1998

Feature-extraction from endopeptidase cleavage sites in mitochondrial targeting peptides.

Cleavage sites in nuclear-encoded mitochondrial protein targeting peptides (mTPs) from mammals, yeast, and plants have been analysed for characteristic physicochemical features using statistical methods, perceptrons, multilayer neural networks, and self-organizing feature maps. Three different sequence motifs were found, revealing loosely defined arginine motifs with Arg in positions -10, -3, and -2. A self-organizing feature map was able to cluster these three types of endopeptidase target sites but did not identify any species-specific characteristics in mTPs. Neural networks were used to define local sequence features around precursor cleavage sites.

Amino Acid Sequence↗
PubMed1997

The complete genome sequence of the gastric pathogen Helicobacter pylori.

Helicobacter pylori, strain 26695, has a circular genome of 1,667,867 base pairs and 1,590 predicted coding sequences. Sequence analysis indicates that H. pylori has well-developed systems for motility, for scavenging iron, and for DNA restriction and modification. Many putative adhesins, lipoproteins and other outer membrane proteins were identified, underscoring the potential complexity of host-pathogen interaction. Based on the large number of sequence-related genes encoding outer membrane proteins and the presence of homopolymeric tracts and dinucleotide repeats in coding sequences, H. pylori, like several other mucosal pathogens, probably uses recombination and slipped-strand mispairing within repeats as mechanisms for antigenic variation and adaptive evolution. Consistent with its restricted niche, H. pylori has a few regulatory networks, and a limited metabolic repertoire and biosynthetic capacity. Its survival in acid conditions depends, in part, on its ability to establish a positive inside-membrane potential in low pH.

Antigenic Variation↗
PubMed1997

Architecture of helix bundle membrane proteins: an analysis of cytochrome c oxidase from bovine mitochondria.

We have analyzed the structure of mitochondrial cytochrome c oxidase in terms of general characteristics thought to be important for describing the architecture of helix bundle membrane proteins. Many aspects of the structure are similar to what has previously been found for the photosynthetic reaction center and bacteriorhodopsin. Our results lead to a considerably more precise general picture of membrane protein architecture than has hitherto been possible to obtain.

Amino Acids↗
PubMed1997

Prediction of transmembrane alpha-helices in prokaryotic membrane proteins: the dense alignment surface method.

A new, simple method for predicting transmembrane segments in integral membrane proteins has been developed. It is based on low-stringency dot-plots of the query sequence against a collection of non-homologous membrane proteins using a previously derived scoring matrix [Cserzö et al., 1994, J. Mol. Biol., 243, 388-396]. This so-called dense alignment surface (DAS) method is shown to perform on par with earlier methods that require extra information in the form of multiple sequence alignments or the distribution of positively charged residues outside the transmembrane segments, and thus improves prediction abilities when only single-sequence information is available or for classes of membrane proteins that do not follow the 'positive inside' rule.

Cell Membrane↗
PubMed1995

Properties of N-terminal tails in G-protein coupled receptors: a statistical study.

The extramembraneous segments in a large collection of G-protein coupled receptors (GPCRs) have been analysed in terms of amino acid composition and length. It is shown that this family of multi-spanning integral membrane proteins conforms well to the 'positive inside' rule. Further, the extracellular N-terminal tails of GPCRs lacking a cleavable signal peptide are shown to be considerably shorter and to have a reduced content of positively charged amnio acids compared with the N-terminal tails of GPCRs endowed with a signal peptide. This suggests that extracellular N-terminal tails of eukaryotic plasma membrane proteins may be translocated by different mechanisms depending on whether or not they are preceded by a signal peptide.

Amino Acid Sequence↗
PubMed1995

Health promotion in schools: policies and practices in Stockholm county, 1990.

A survey was undertaken of the policies and practices concerning organisation and implementation of health education and health promotion in schools in 151 of the total 213 Local Educational Areas (LEAs) in Stockholm county in 1990. Health education was included in the workplan of 49% of the responding LEAs, while 39% of respondents had a local action programme or guidelines for health education. Topic areas taught to all pupils and considered most important included alcohol, drug abuse, smoking, sex education, bullying, nutrition and physical exercise. Most senior level schools (55-83%) had written policies concerning pupils using alcohol, drugs or smoking in school, and 68% of LEAs had restrictions on staff smoking in school. Continuing health education was desired by 87% of the respondents. A written programme/plan regarding health education was identified as an important indicator of interest and commitment in health education and health policy issues by the local school.

Adolescent↗
PubMed1993

Cancer prevention in schools: design and pilot testing of a nutritional curriculum for mid-adolescents.

Adolescents at schools ought to be easy to reach for dietary cancer prevention programs. Yet, traditional school health education interventions, however, do not affect behavior. We have a developed short-term (10 hour) program that supports adolescents in adopting a low-fat, high-fiber diet. The aim has been achieved by making the classroom activities work as part of a community intervention program and by including elements derived from Bandura's social learning theory and the self-efficacy construct. Following the theoretical constructs, the students are exposed to peers reporting on appropriate dietary behavior. In order to enhance self-efficacy, students are given the opportunity to experience successful self-initiated dietary changes. Thus, they set up an individual dietary goal and carry out changes based on this. A pilot test indicated that the program process works as planned. However, in order to evaluate behavioral effects, further studies are required.

Adolescent↗
PubMed1991

The effects of 6-OHDA-induced dopamine depletions in the ventral or dorsal striatum on maternal and sexual behavior in the female rat.

The effects of dopamine-depleting 6-OHDA infusions in the ventral or dorsal striatum on maternal and sexual behaviors were examined in female rats. Like sham-operated controls, lactating rats receiving 6-OHDA in the ventral striatum built good nests, nursed the infants and showed maternal aggression toward strange intruders. By contrast, the lesioned females performed poorly in tests for pup retrieval, as reflected in greatly protracted retrieval latencies. There was no effect of ventral striatal DA depletions on proceptive and receptive elements of female sexual behavior, which was studied after lactation following ovariectomy and exogenous administration of ovarian hormones, but these animals did show an attenuated hyperactivity response to a low dose of amphetamine. Females with dopamine lesions in the dorsal striatum did not differ from controls with respect to maternal and sexual behavior, but they did show an enhanced hyperactivity response to amphetamine treatment.

Amphetamine↗
PubMed1991

Mesotelencephalic dopamine system and reproductive behavior in the female rat: effects of ventral tegmental 6-hydroxydopamine lesions on maternal and sexual responsiveness.

The effects of lesions to the mesolimbic dopamine system on maternal and sexual behaviors in the female rat was assessed. Rat dams that were given ventral tegmental area microinfusions of 6-hydroxydopamine (6-OHDA) during lactation showed a persistent deficit in pup retrieval but were not impaired with respect to nursing, nest building, or maternal aggression. In addition, 6-OHDA-lesioned females failed to respond to amphetamine by showing locomotor hyperactivity. Administration of the dopamine blocker raclopride to neurologically intact dams also inhibited pup retrieval but had no effect on nursing. Females given 6-OHDA during pregnancy appeared completely unresponsive to pups, whereas no maternal deficits were seen in females that received 6-OHDA 8 weeks before parturition. Proceptive (hopping and darting) and receptive (lordosis) components of sexual behavior, assessed after ovariectomy and exogenous steroid hormone treatment, were not affected by mesolimbic 6-OHDA lesions.

Animals↗