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Biomedical subjects

A Helm

Publications and source records attributed to A Helm.

At least 19 recordsLinked to original sources
PubMed2000

Identification of sequence determinants that direct different intracellular folding pathways for aquaporin-1 and aquaporin-4.

Homologous aquaporin water channels utilize different folding pathways to acquire their transmembrane (TM) topology in the endoplasmic reticulum (ER). AQP4 acquires each of its six TM segments via cotranslational translocation events, whereas AQP1 is initially synthesized with four TM segments and subsequently converted into a six membrane-spanning topology. To identify sequence determinants responsible for these pathways, peptide segments from AQP1 and AQP4 were systematically exchanged. Chimeric proteins were then truncated, fused to a C-terminal translocation reporter, and topology was analyzed by protease accessibility. In each chimeric context, TM1 initiated ER targeting and translocation. However, AQP4-TM2 cotranslationally terminated translocation, while AQP1-TM2 failed to terminate translocation and passed into the ER lumen. This difference in stop transfer activity was due to two residues that altered both the length and hydrophobicity of TM2 (Asn(49) and Lys(51) in AQP1 versus Met(48) and Leu(50) in AQP4). A second peptide region was identified within the TM3-4 peptide loop that enabled AQP4-TM3 but not AQP1-TM3 to reinitiate translocation and cotranslationally span the membrane. Based on these findings, it was possible to convert AQP1 into a cotranslational biogenesis mode similar to that of AQP4 by substituting just two peptide regions at the N terminus of TM2 and the C terminus of TM3. Interestingly, each of these substitutions disrupted water channel activity. These data thus establish the structural basis for different AQP folding pathways and provide evidence that variations in cotranslational folding enable polytopic proteins to acquire and/or maintain primary sequence determinants necessary for function.

Amino Acid Sequence↗
PubMed2000

Transmembrane biogenesis of Kv1.3.

Using a combination of protease protection, glycosylation, and carbonate extraction assays, we have characterized the topogenic determinants encoded by Kv1.3 segments that mediate translocation events during endoplasmic reticulum (ER) biogenesis. Transmembrane segments S1, S2, S3, S5, and S6 initiate translocation, only S1 and S2 strongly (>60%) anchor themselves in the membrane, S5 exhibits signal anchor activity and contains a cryptic cleavage site, and S3 and S6 fail to integrate into the membrane. Elongation of each single-transmembrane construct to include multiple transmembrane segments alters integration and translocation efficiencies, indicating that multiple topogenic determinants cooperate during Kv1. 3 topogenesis and assembly. Several surprising findings emerged from these studies. First, in the presence of T1, the N-terminal recognition domain, S1 was unable to initiate either translocation or membrane integration. As a result, S2 likely functions as the initial signal sequence to establish Kv1.3 N-terminus topology. Second, S4 independently integrates into the membrane. Third, S6 plus the C-terminus of Kv1.3 is a secretory protein but can be converted to a membrane-integrated protein with a correctly oriented, cytosolic C-terminus by linking S6 to S5 and the pore loop. These results have implications for the role of the N-terminus in Kv biogenesis and on the mechanisms of dominant negative suppression of Kv1.3 by truncated Kv1.3 fragments [Tu et al. (1996) J. Biol. Chem. 271, 18904-18911].

Amino Acid Sequence↗
PubMed1999

Liability, UAPs and you.

Supervising unlicensed employees increases your malpractice risks. To protect yourself, learn what courts and juries have had to say when patients sue.

Humans↗
PubMed1998

Co- and posttranslational translocation mechanisms direct cystic fibrosis transmembrane conductance regulator N terminus transmembrane assembly.

Transmembrane topology of most eukaryotic polytopic proteins is established cotranslationally at the endoplasmic reticulum membrane through the action of alternating signal and stop transfer sequences. Here we demonstrate that the cystic fibrosis transmembrane conductance regulator (CFTR) achieves its N terminus topology through a variation of this mechanism that involves both co- and posttranslational translocation events. Using a series of defined chimeric and truncated proteins expressed in a reticulocyte lysate system, we have identified two topogenic determinants encoded within the first (TM1) and second (TM2) membrane-spanning segments of CFTR. Each sequence independently (i) directed endoplasmic reticulum targeting, (ii) translocated appropriate flanking residues, and (iii) achieved its proper membrane-spanning orientation. Signal sequence activity of TM1, however, was inefficient due to the presence of two charged residues, Glu92 and Lys95, located within its hydrophobic core. As a result, TM1 was able to direct correct topology for less than half of nascent CFTR chains. In contrast to TM1, TM2 signal sequence activity was both efficient and specific. Even in the absence of a functional TM1 signal sequence, TM2 was able to direct CFTR N terminus topology through a ribosome-dependent posttranslational mechanism. Mutating charged residues Glu92 and Lys95 to alanine improved TM1 signal sequence activity as well as the ability of TM1 to independently direct CFTR N terminus topology. Thus, a single functional signal sequence in either the first or second TM segment was sufficient for directing proper CFTR topology. These results identify two distinct and redundant translocation pathways for CFTR N terminus transmembrane assembly and support a model in which TM2 functions to ensure correct topology of CFTR chains that fail to translocate via TM1. This novel arrangement of topogenic information provides an alternative to conventional cotranslational pathways of polytopic protein biogenesis.

Amino Acid Sequence↗
PubMed1998

Coupled translocation events generate topological heterogeneity at the endoplasmic reticulum membrane.

Topogenic determinants that direct protein topology at the endoplasmic reticulum membrane usually function with high fidelity to establish a uniform topological orientation for any given polypeptide. Here we show, however, that through the coupling of sequential translocation events, native topogenic determinants are capable of generating two alternate transmembrane structures at the endoplasmic reticulum membrane. Using defined chimeric and epitope-tagged full-length proteins, we found that topogenic activities of two C-trans (type II) signal anchor sequences, encoded within the seventh and eighth transmembrane (TM) segments of human P-glycoprotein were directly coupled by an inefficient stop transfer (ST) sequence (TM7b) contained within the C-terminus half of TM7. Remarkably, these activities enabled TM7 to achieve both a single- and a double-spanning TM topology with nearly equal efficiency. In addition, ST and C-trans signal anchor activities encoded by TM8 were tightly linked to the weak ST activity, and hence topological fate, of TM7b. This interaction enabled TM8 to span the membrane in either a type I or a type II orientation. Pleiotropic structural features contributing to this unusual topogenic behavior included 1) a short, flexible peptide loop connecting TM7a and TM7b, 2) hydrophobic residues within TM7b, and 3) hydrophilic residues between TM7b and TM8.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed1997

Dietitians in breastfeeding management: an untapped resource in the hospital.

Maternity care nurses were surveyed to gather data on the state of breastfeeding in Utah hospitals. A questionnaire was distributed to labor and delivery, well-baby nursery, and postpartum nurses at 18 hospitals representing 86% of births in the state. The results indicated that of dietitians, physicians, and nurses, dietitians were the health care professionals least likely to provide breastfeeding information and assistance.

Adult↗
PubMed1996

Respiratory rehabilitation, exercise capacity and quality of life in chronic airways disease in old age.

Respiratory rehabilitation improves exercise capacity and quality of life in younger patients but is untried in the aged. We aimed to: (a) assess repeatability of the 6-minute walk test, factors affecting it and its relation to quality of life in elderly patients with chronic obstructive airways disease (COAD); (b) assess compliance of such patients with an intensive respiratory rehabilitation protocol; (c) pilot the assessment of the effect of respiratory rehabilitation on the 6-minute walk test in these patients. Seventeen subjects with stable, symptomatic COAD were recruited, 15 (six men), 70-89 (mean 76) years, completed the study. Mean (standard deviation) 1-second forced expiratory volume (FEV1) = 49 (5)% predicted. Six-minute walk tests were repeated single-blind, 2-10 days apart. Quality of life was measured using Guyatt respiratory questionnaire. Patients underwent 12 weeks incremental respiratory rehabilitation (x4/day step-ups, unweighed arm raises, inflating balloons). Baseline 6-minute walk was repeatable and was correlated with the log Guyatt dyspnoea score (r = 0.65, p = 0.006). In multiple regression neither age nor FEV1 predicted walk distance: body mass index, maximal expiratory mouth pressure; calorie intake. Mean (SEM) 6-minute walk distance after-rehabilitation was greater than baseline (p = 0.003). Elderly patients with COAD tolerate intensive respiratory rehabilitation and a controlled, blinded study is needed.

Aged↗
PubMed1986

Elder abuse.

Explore the source record for details and available documents.

Aged↗
PubMed1985

Truth telling, placebos, and deception: ethical and legal issues in practice.

The issue of truth-telling is very complex. There is variance among patients in the amount of information they want to be told and variance among professionals in the amount of information they want to tell. Truth is conditioned by our knowledge limits and understanding. Technological advances in health care have made this arena even more complex. Placebos have been viewed traditionally as a kind of benign deception. Few studies have looked at treatments and tests as placebos. There are many myths associated with placebos and placebo therapy. There are five primary theories for withholding the truth or promoting deception with patients. Ethical and legal principles generally support veracity and the concept of a duty to tell the truth. One of the remaining issues is whether the placebo effect can be achieved without deception.

Aerospace Medicine↗
PubMed1984

Ethical dilemmas and nursing.

Professional responsibilities, tradition, and personal conscience along with legal, philosophical, and religious convictions dictate nursing interventions. Inevitably, these factors embrace life-sustaining therapies; however, in view of complications, prognosis, pain and suffering, and their own views of quality of life, some patients express wishes inconsistent with life-sustaining measures. In other situations, the health care provider as well as the patient may view heroic efforts as more debilitating than resortative. Resolving the conflict while preserving the patient's best interests requires a confrontation with the status of "do-not resuscitate" policies within th e nurse's institution, informed consent, refusal, and competency as the necessary underpinnings for the development of an ethical and legal posture within the profession, with which to approach significant decisions regarding life-sustaining therapies. Literally every hour of every day nurses are immediately and directly involved with resolving ethical dilemmas based upon judgements and interpretations of oral or written orders, patient and family wishes, professional training, and an infinite number of other factors. When clear policies or orders are lacking, the nurse is left with the burden of making a life or death decision. It is imperative that professional nurses assess the administrative, legal, and ethical ramifications of their actions in terms of ethical codes of practice, patients' rights, institutional and personal liability, civil and criminal laws, and private conscience. An understanding of these issues, passive and active euthansia, state and national trends, and uniform legislation can assist in resolutions of the no-code dilemma. Nursing as a profession must strive to develop sound and consistent guidelines and rationale for the scope of practice in ethical dilemmas.

Conflict, Psychological↗