Sorting of proteins to vacuoles in plant cells

An individual plant cell may contain at least two functionally and structurally distinct types of vacuoles: protein storage vacuoles and lytic vacuoles. Presumably a cell that stores proteins in vacuoles must maintain these separate compartments to prevent exposure of the storage proteins to an acidified environment with active hydrolytic enzymes where they would be degraded. Thus, the organization of the secretory pathway in plant cells, which includes the vacuoles, has a fascinating complexity not anticipated from the extensive genetic and biochemical studies of the secretory pathway in yeast. Plant cells must generate the membranes to form two separate types of tonoplast, maintain them as separate organelles, and direct soluble proteins from the secretory flow specifically to one or the other via separate vesicular pathways. Individual soluble and membrane proteins must be recognized and sorted into one or the other pathway by distinct, specific mechanisms. Here we review the emerging picture of how separate plant vacuoles are organized structurally and how proteins are recognized and sorted to each type.

Chemical and biological studies of a new cigarette that primarily heats tobacco. Part 1. Chemical composition of mainstream smoke

A new-technology cigarette has been developed. While the new cigarette burns some tobacco, it does not use tobacco as the fuel to sustain combustion and provide heat to the cigarette. Rather, the new cigarette primarily heats tobacco thereby reducing products of smoke formation mechanisms such as tobacco combustion, tobacco pyrolysis and pyrosynthesis. The mainstream smoke composition from a cigarette based on the new design (TOB-HT) has been characterized in comparative chemical testing with two reference cigarettes using the FTC puffing regimen. Thermal properties, UV absorption characteristics, elemental composition and materials balance studies all suggest a simplified smoke aerosol. Twenty-five smoke constituents ("target compounds") identified by the scientific community as compounds that may contribute to the diseases statistically associated with smoking have also been measured. Mainstream smoke concentrations of most target compounds are significantly lower with the TOB-HT cigarette when compared with reference cigarettes in the ultra-light "tar" and light "tar" categories. Taken together, chemical analysis results suggest simplified TOB-HT smoke chemistry with marked reductions in specific chemicals reported to be biologically active.

Chemical and biological studies of a new cigarette that primarily heats tobacco. Part 1. Chemical composition of mainstream smoke

A new-technology cigarette has been developed. While the new cigarette burns some tobacco, it does not use tobacco as the fuel to sustain combustion and provide heat to the cigarette. Rather, the new cigarette primarily heats tobacco thereby reducing products of smoke formation mechanisms such as tobacco combustion, tobacco pyrolysis and pyrosynthesis. The mainstream smoke composition from a cigarette based on the new design (TOB-HT) has been characterized in comparative chemical testing with two reference cigarettes using the FTC puffing regimen. Thermal properties, UV absorption characteristics, elemental composition and materials balance studies all suggest a simplified smoke aerosol. Twenty-five smoke constituents ("target compounds") identified by the scientific community as compounds that may contribute to the diseases statistically associated with smoking have also been measured. Mainstream smoke concentrations of most target compounds are significantly lower with the TOB-HT cigarette when compared with reference cigarettes in the ultra-light "tar" and light "tar" categories. Taken together, chemical analysis results suggest simplified TOB-HT smoke chemistry with marked reductions in specific chemicals reported to be biologically active.

Electrophysiological and biochemical evidence that DEG/ENaC cation channels are composed of nine subunits

Members of the DEG/ENaC protein family form ion channels with diverse functions. DEG/ENaC subunits associate as hetero- and homomultimers to generate channels; however the stoichiometry of these complexes is unknown. To determine the subunit stoichiometry of the human epithelial Na+ channel (hENaC), we expressed the three wild-type hENaC subunits (alpha, beta, and gamma) with subunits containing mutations that alter channel inhibition by methanethiosulfonates. The data indicate that hENaC contains three alpha, three beta, and three gamma subunits. Sucrose gradient sedimentation of alphahENaC translated in vitro, as well as alpha-, beta-, and gammahENaC coexpressed in cells, was consistent with complexes containing nine subunits. FaNaCh and BNC1, two related DEG/ENaC channels, produced complexes of similar mass. Our results suggest a novel nine-subunit stoichiometry for the DEG/ENaC family of ion channels.

Molecular cloning and further characterization of a probable plant vacuolar sorting receptor

BP-80 is a type I integral membrane protein abundant in pea (Pisum sativum) clathrin-coated vesicles (CCVs) that binds with high affinity to vacuole-targeting determinants containing asparagine-proline-isoleucine-arginine. Here we present results from cDNA cloning and studies of its intracellular localization. Its sequence and sequences of homologs from Arabidopsis, rice (Oryza sativa), and maize (Zea mays) define a novel family of proteins unique to plants that is highly conserved in both monocotyledons and dicotyledons. The BP-80 protein is present in dilated ends of Golgi cisternae and in "prevacuoles," which are small vacuoles separate from but capable of fusing with lytic vacuoles. Its cytoplasmic tail contains a Tyr-X-X-hydrophobic residue motif associated with transmembrane proteins incorporated into CCVs. When transiently expressed in tobacco (Nicotiana tabacum) suspension-culture protoplasts, a truncated form lacking transmembrane and cytoplasmic domains was secreted. These results, coupled with previous studies of ligand-binding specificity and pH dependence, strongly support our hypothesis that BP-80 is a vacuolar sorting receptor that trafficks in CCVs between Golgi and a newly described prevacuolar compartment.

Monoclonal antibodies to barley aleurain and homologs from other plants

Barley aleurain is contained within a specific type of vacuole characterized by acidic pH and the presence of other hydrolytic enzymes. The aleurain-containing vacuole is distinct from protein storage vacuoles, and anti-aleurain antibodies serve as markers for this organelle in barley cells. Aleurain is a unique type of cysteine protease, and other plant species have genes for homologs whose sequences are highly conserved, but little is known about these homologs at the protein level. Seven monoclonal antibodies to barley aleurain were isolated, which bind to and define aleurain homologues in Arabidopsis, Petunia, and tobacco cell extracts. Interestingly, in addition to 29-32 kDa aleurain homologs, Petunia extracts contain a protein of approximately 50 kDa and tobacco extracts a protein of approximately 40 kDa that are recognized by multiple different monoclonal antibodies, indicating an unexpected diversity to the aleurain protein family. Among the group of antibodies are some that efficiently immunoprecipitate metabolically labeled aleurain from barley cell extracts, and some that efficiently label aleurain in immunofluorescence assays using root tip cells. These antibodies should be useful for plant cell biologists who study vacuole biogenesis and function and sorting of proteins to specific vacuolar compartments, in barley as well as other plant species.

Evaluation of daily living tasks: the home care advantage

Occupational therapists working in home care have an advantage over those working in other settings because they can observe the influence of the naturalistic context on task performance. However, to use this advantage, therapists working in home care must use an evaluation approach that enables them to capture the client-task-context transaction. In this article, we discuss the ability of four "evaluation approaches"--norm-referenced, criterion-referenced, dynamic, informal--to provide information about the client-task-context transaction that therapists need in order to plan effective intervention. The potential of each approach for identifying clients' performance problems, suggesting etiologies, determining rehabilitation potential, and guiding intervention is analyzed, and the appropriateness of each approach for application in the home is appraised. This analysis highlights the utility of combining the criterion-referenced and dynamic assessment approaches for use in home care. A sequential process for integrating these two approaches is provided, and the proposed outcomes to be obtained from this process are identified.

Reciprocal translocation 4;11 with both adjacent-1 segregants viable within a family

We describe a family carrying a balanced 4;11 translocation in which both adjacent-1 segregants are viable. The proband had an unbalanced karyotype: 46,XY,der(11)t(4;11)(q34.3;q23.1)mat. At 8.5 years of age he showed trigonocephaly, hypertelorism, epicanthal folds, down-slanting palpebral fissures, low-set ears, anteverted nares, down-turned carp-shaped mouth, and bilateral fifth finger clinodactyly. His maternal aunt was also dysmorphic with high-arched palate, short philtrum and mild developmental delay. Her karyotype was 46,XX,der(4)t(4;11)(q34.3;q23.1)pat. Other relatives who likely carried a chromosomally unbalanced segregant were identified from photographs and medical records. We compare the clinical findings in our family with descriptions of other similar karyotypic abnormalities from previous case reports.

Phosphorylation of S1505 in the cardiac Na+ channel inactivation gate is required for modulation by protein kinase C

Inactivation of both brain and cardiac Na+ channels is modulated by activation of protein kinase C (PKC) but in different ways. Previous experiments had shown that phosphorylation of serine 1506 in the highly conserved loop connecting homologous domains III and IV (LIII/IV) of the brain Na+ channel alpha subunit is necessary for all effects of PKC. Here we examine the importance of the analogous serine for the different modulation of the rH1 cardiac Na+ channel. Serine 1505 of rH1 was mutated to alanine to prevent its phosphorylation, and the resulting mutant channel was expressed in 1610 cells. Electrophysiological properties of these mutant channels were indistinguishable from those of wild-type (WT) rH1 channels. Activation of PKC with 1-oleoyl-2-acetyl-sn-glycerol (OAG) reduced WT Na+ current by 49.3 +/- 4.2% (P < 0.01) but S1505A mutant current was reduced by only 8.5 +/- 5.4% (P = 0.29) when the holding potential was -94 mV. PKC activation also caused a -17-mV shift in the voltage dependence of steady-state inactivation of the WT channel which was abolished in the mutant. Thus, phosphorylation of serine 1505 is required for both the negative shift in the inactivation curve and the reduction in Na+ current by PKC. Phosphorylation of S1505/1506 has common and divergent effects in brain and cardiac Na+ channels. In both brain and cardiac Na+ channels, phosphorylation of this site by PKC is required for reduction of peak Na+ current. However, phosphorylation of S1506 in brain Na+ channels slows and destabilizes inactivation of the open channel. Phosphorylation of S1505 in cardiac, but not S1506 in brain, Na+ channels causes a negative shift in the inactivation curve, indicating that it stabilizes inactivation from closed states. Since LIII/IV containing S1505/S1506 is completely conserved, interaction of the phosphorylated serine with other regions of the channel must differ in the two channel types.

Comparison of standard and alternative health assessment questionnaire scoring procedures for documenting functional outcomes in patients with rheumatoid arthritis

OBJECTIVE

To compare statistical properties of data from the Health Assessment Questionnaire (HAQ) with those from an alternative version (AHAQ) that used a different scoring system for the item categories and disability index. Comparisons included descriptive statistics, correlations, and inferential statistics to determine whether the AHAQ would be a more sensitive measure of change in functional status.

METHODS

The subjects were 107 adults diagnosed with rheumatoid arthritis and hospitalized for exacerbations in their arthritis or arthritis related joint surgery. Disability was assessed upon admission to hospital and at one year followup with the HAQ. AHAQ scores were generated for the item categories making up the disability index by taking the mean of the item scores in a category instead of the worst item score; the disability index was the mean of the alternative category scores.

RESULTS

The standard method of scoring the HAQ was found to generate greater variance on category scores, lower correlations between category scores and the total disability index, and lower correlations between first and 2nd administrations of the instrument, compared to the AHAQ. HAQ disability index scores also correlated slightly lower than those of AHAQ to scores from the HAQ pain scales, and to scores from 2 other measures of functional disability. In addition, the AHAQ was found to be more powerful in detecting functional changes at one year followup.

CONCLUSION

Because of its statistical properties the AHAQ scoring method may be preferable to the HAQ method when the instrument is used for documenting change in functional outcomes.

Molecular determinants of high affinity binding of alpha-scorpion toxin and sea anemone toxin in the S3-S4 extracellular loop in domain IV of the Na+ channel alpha subunit

alpha-Scorpion toxins and sea anemone toxins bind to a common extracellular site on the Na+ channel and inhibit fast inactivation. Basic amino acids of the toxins and domains I and IV of the Na+ channel alpha subunit have been previously implicated in toxin binding. To identify acidic residues required for toxin binding, extracellular acidic amino acids in domains I and IV of the type IIa Na+ channel alpha subunit were converted to neutral or basic amino acids using site-directed mutagenesis, and altered channels were transiently expressed in tsA-201 cells and tested for 125I-alpha-scorpion toxin binding. Conversion of Glu1613 at the extracellular end of transmembrane segment IVS3 to Arg or His blocked measurable alpha-scorpion toxin binding, but did not affect the level of expression or saxitoxin binding affinity. Conversion of individual residues in the IVS3-S4 extracellular loop to differently charged residues or to Ala identified seven additional residues whose mutation caused significant effects on binding of alpha-scorpion toxin or sea anemone toxin. Moreover, chimeric Na+ channels in which amino acid residues at the extracellular end of segment IVS3 of the alpha subunit of cardiac Na+ channels were substituted into the type IIa channel sequence had reduced affinity for alpha-scorpion toxin characteristic of cardiac Na+ channels. Electrophysiological analysis showed that E1613R has 62- and 82-fold lower affinities for alpha-scorpion and sea anemone toxins, respectively. Dissociation of alpha-scorpion toxin is substantially accelerated at all potentials compared to wild-type channels. alpha-Scorpion toxin binding to wild type and E1613R had similar voltage dependence, which was slightly more positive and steeper than the voltage dependence of steady-state inactivation. These results indicate that nonidentical amino acids of the IVS3-S4 loop participate in alpha-scorpion toxin and sea anemone toxin binding to overlapping sites and that neighboring amino acid residues in the IVS3 segment contribute to the difference in alpha-scorpion toxin binding affinity between cardiac and neuronal Na+ channels. The results also support the hypothesis that this region of the Na+ channel is important for coupling channel activation to fast inactivation.

COMPARTMENTATION OF PROTEINS IN THE ENDOMEMBRANE SYSTEM OF PLANT CELLS

This review focuses on four interrelated processes in the plant endomembrane system: compartmentation of proteins in subdomains of the endoplasmic reticulum, mechanisms that determine whether storage proteins are retained within the ER lumen or transported out, the origin and function of biochemically distinct vacuoles or prevacuolar organelles, and the cellular processes by which proteins are sorted to vacuolar compartments. We postulate that ER-localized protein bodies are formed by a series of orderly events of protein synthesis, protein concentration, and protein assembly in subdomains of the ER. Protein concentration, which facilitates protein-to-protein interactions and subsequent protein assembly, may be achieved by the interactions with chaperones and by the localization of storage protein mRNAs. We also describe recent developments on the coexistence of two biochemically distinguishable vacuolar compartments, the possible direct role of the ER in vacuole biogenesis, and proposed mechanisms for transport of proteins from the ER or Golgi apparatus to the vacuole.

Plant cells contain two functionally distinct vacuolar compartments

The plant cell vacuole has multiple functions, including storage of proteins and maintenance of an acidic pH where proteases will have maximal activity. It has been assumed that these diverse functions occur in the same compartment. Here, we demonstrate that antibodies to two different tonoplast intrinsic proteins, alpha-TIP and TIP-Ma27, label vacuole membranes of two different compartments within the same cell. These compartments are functionally distinct, because barley lectin, a protein stored in root tips, is exclusively contained within the alpha-TIP compartment, while aleurain, a protease that serves as a marker for an acidified vacuolar environment, is exclusively contained within the TIP-Ma27 compartment. As cells develop large vacuoles, the two compartments merge; this may represent a process by which storage products in the alpha-TIP compartment are exposed to the acidic lytic TIP-Ma27 compartment for degradation.

Modulation of cardiac Na+ channel expression in Xenopus oocytes by beta 1 subunits

Voltage-gated Na+ channels consist of a large alpha subunit of 260 kDa associated with beta 1 and/or beta 2 subunits of 36 and 33 kDa, respectively. alpha subunits of rat cardiac Na+ channels (rH1) are functional when expressed alone in Xenopus oocytes or mammalian cells. beta 1 subunits are present in the heart, and localization of beta 1 subunit mRNA by in situ hybridization shows expression in the perinuclear cytoplasm of cardiac myocytes. Coexpression of beta 1 subunits with rH1 alpha subunits in Xenopus oocytes increases Na+ currents up to 6-fold in a concentration-dependent manner. However, no effects of beta 1 subunit coexpression on the kinetics or voltage dependence of the rH1 Na+ current were detected. Increased expression of Na+ currents is not observed when an equivalent mRNA encoding a nonfunctional mutant beta 1 subunit is coexpressed. Our results show that beta 1 subunits are expressed in cardiac muscle cells and that they interact with alpha subunits to increase the expression of cardiac Na+ channels in Xenopus oocytes, suggesting that beta 1 subunits are important determinants of the level of excitability of cardiac myocytes in vivo.

Comparison of the effects of N6-methyldeoxyadenosine and N5-methyldeoxycytosine on transcription from nuclear gene promoters in barley

Methylation of deoxycytosine residues in plant nuclear DNA at CpG dinucleotides is generally assumed to suppress transcription, while deoxyadenosine methylation on recombinant reporter gene constructs transiently introduced into plant cells increases expression by uncharacterized mechanisms. A particle bombardment transient expression system was used in intact barley aleurone layers to quantitate the effects of CpG and A methylation on transcription from well-characterized hormone-regulated alpha-amylase promoters. Methylation of C in all CpG pairs had little effect on transcription. In contrast, the presence of methylated A residues in the sequence GATC scattered in the reporter plasmid outside of the promoter increased transcription two- to fivefold, regardless of the strength of the promoter, and proper hormonal regulation of transcription was maintained. The methyl-dA effect was similar when the amount of reporter construct DNA used was varied over a 20-fold range, beginning with an amount that gave only a small increment of expression above background. Similar enhancing effects for methyl-dA were seen with the CaMV 35S, maize Adh1, and maize ubiquitin promoters, though the magnitude varied for each individual promoter. Methyl-dA did not detectably affect plasmid DNA stability in aleurone cells in transient expression experiments because the enhancing effect of methyl-dA on expression was the same regardless of whether the assay was performed at 12 h or 40 h. Several proteins in wheat germ nuclear extracts bound preferentially to methylated DNA as assessed by gel retardation assays; one showed preferential binding to methyl-dA rather than methyl-CpG residues. The data indicate that the presence of methyl-dA in the vicinity of active promoters enhances transcription of nuclear genes in barley in a manner independent of the strength of the promoter. This effect may be mediated by a methyl-dA-binding protein.

Can physicians use family genogram information to identify patients at risk of anxiety or depression?

Advocates of family-oriented care assert that physicians' use of family genograms can improve clinical practice, such as in the recognition of patients' emotional problems. The purpose of this article is to investigate whether physicians could use family genogram information to identify their patients at high risk of the two most common mental disorders, anxiety and depression. Physicians' use of family genograms to stratify their patients' risk raises two questions about the information recorded on the genograms: is family information reliable and valid, and is family information associated with anxiety and depression? A review of the published epidemiological literature revealed that some basic family information recorded on genograms is useful for risk stratification.

Stability and change in functional assessment of patients with geropsychiatric disorders

OBJECTIVES

Functional assessments of patients with geropsychiatric disorders accomplished by self-rating, informant rating, and performance test were compared.

METHOD

Fifty-eight inpatients with major depression or progressive dementia were evaluated on three occasions over 6 months with informant and patient versions of the Activities of Daily Living Scale of the Older Americans Resources and Services Multidimensional Functional Assessment (OARS-ADL) and with the Performance Assessment of Self-Care Skills (PASS).

RESULTS

Patients' scores became significantly worse (p < .01) on the informant version of the OARS-ADL and the PASS. Self-ratings with the OARS-ADL did not worsen significantly (p > .05).

CONCLUSION

Agreement between informant rating and performance test concerning functional status of patients with dementia was good. Elderly patients with depression may experience subtle deterioration that only becomes apparent on performance tests.

Inhibitory activity of cigarette-smoke condensate on the mutagenicity of heterocyclic amines

Cigarette-smoke condensate (CSC) is a complex mixture containing over 3800 identified chemicals including nicotine, water, mutagens, antimutagens, cytotoxins and inert chemicals. Although CSC is mutagenic in the Ames test, its effect on the activity of other mutagens has not been characterized. Using the Ames Salmonella bacterial mutagenesis assay, we found CSC exerts a significant inhibitory effect on mutagens requiring bioactivation. Those studied included heterocyclic amines (Glu-P-1, Glu-P-2, IQ, MeIQ, Trp-P-1 and Trp-P-2), benzo[a]pyrene (B[a]P) and aflatoxin B1. However, CSC had no effect on the activity of direct-acting mutagens (2-nitrofluorene, sodium azide, 4-nitro-1,2-phenylenediamine, 4-nitroquinoline N-oxide and methyl methanesulfonate). With indirect-acting mutagens, the reduced number of revertants observed in the presence of CSC was not attributable to cytotoxicity. CSC exhibited a potent inhibitory effect on the cytochrome P-450 dependent monooxygenases, ethoxyresorufin O-deethylase and B[a]P hydroxylase. This suggests inhibition of the cytochrome P-450 isozymes as one possible mechanism for the antimutagenicity of CSC. Fractionation studies of CSC revealed that the neutral, weakly acidic (phenolic) and basic fractions are all effective as antimutagens against Glu-P-1, a representative heterocyclic amine. This indicates that several classes of chemicals contribute to the inhibitory effect of CSC on the mutagenicity of the heterocyclic amines.

Systemic thinking: how do we know it when we see it?

One discussion within the field of family-oriented care concerns the distinction between those who practise a family approach and those who think in family system terms. This paper presents a comprehensive model of systemic thinking that may be useful for both family systems teachers and researchers. The conceptual model includes: (i) clinicians' experiences with and attitudes towards family aspects of health problems, and the context of clinicians' judgements about these problems; (ii) the way clinicians organize their knowledge about family factors and health problems in order for that knowledge to be readily available for decision making; and (iii) the interview sequences and hypothesis-generating or testing strategies used by clinicians in encounters with patients. The extent to which clinicians exhibit systemic thinking can be determined through interviews, questionnaires and case materials such as encounter transcripts. A method that assesses systemic thinking allows rigorous evaluations of family-oriented teaching efforts and clinical interventions.