1
|
Ribeiro SCC, Arantes Lopes TA, Costa JVG, Rodrigues CG, Maia IWA, Soler LDM, Marchini JFM, Neto RAB, Souza HP, Alencar JCG. The Physician Surprise Question in the Emergency Department: prospective cohort study. BMJ Support Palliat Care 2024:spcare-2024-004797. [PMID: 38316516 DOI: 10.1136/spcare-2024-004797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2024] [Accepted: 01/22/2024] [Indexed: 02/07/2024]
Abstract
OBJECTIVES This study aims to test the ability of the surprise question (SQ), when asked to emergency physicians (EPs), to predict in-hospital mortality among adults admitted to an emergency room (ER). METHODS This prospective cohort study at an academic medical centre included consecutive patients 18 years or older who received care in the ER and were subsequently admitted to the hospital from 20 April 2018 to 20 October 2018. EPs were required to answer the SQ for all patients who were being admitted to hospital. The primary outcome was in-hospital mortality. RESULTS The cohort included 725 adults (mean (SD) age, 60 (17) years, 51% men) from 58 128 emergency department (ED) visits. The mortality rates were 20.6% for 30-day all-cause in-hospital mortality and 23.6% for in-hospital mortality. The diagnostic test characteristics of the SQ have a sensitivity of 53.7% and specificity of 87.1%, and a relative risk of 4.02 (95% CI 3.15 to 5.13), p<0.01). The positive and negative predictive values were 57% and 86%, respectively; the positive likelihood ratio was 4.1 and negative likelihood ratio was 0.53; and the accuracy was 79.2%. CONCLUSIONS We found that asking the SQ to EPs may be a useful tool to identify patients in the ED with a high risk of in-hospital mortality.
Collapse
Affiliation(s)
| | | | - Jose Victor Gomes Costa
- Disciplina de Emergências Clínicas, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
| | - Caio Godoy Rodrigues
- Disciplina de Emergências Clínicas, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
| | - Ian Ward Abdalla Maia
- Disciplina de Emergências Clínicas, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
| | - Lucas de Moraes Soler
- Disciplina de Emergências Clínicas, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
| | | | | | - Heraldo Possolo Souza
- Disciplina de Emergências Clínicas, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
| | - Júlio César Garcia Alencar
- Disciplina de Emergências Clínicas, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
- Universidade de São Paulo Faculdade de Odontologia de Bauru, Bauru, Brazil
| |
Collapse
|
2
|
Silva MP, Rodrigues CG, Machado DC, Nogueira RA. Long-term memory in Staphylococcus aureus α-hemolysin ion channel kinetics. Eur Biophys J 2023; 52:661-671. [PMID: 37542583 DOI: 10.1007/s00249-023-01675-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Revised: 07/03/2023] [Accepted: 07/20/2023] [Indexed: 08/07/2023]
Abstract
The kinetics of an ion channel are classically understood as a random process. However, studies have shown that in complex ion channels, formed by multiple subunits, this process can be deterministic, presenting long-term memory. Staphylococcus aureus α-hemolysin (α-HL) is a toxin that acts as the major factor in Staphylococcus aureus virulence. α-HL is a water-soluble protein capable of forming ion channels into lipid bilayers, by insertion of an amphipathic β-barrel. Here, the α-HL was used as an experimental model to study memory in ion channel kinetics. We applied the approximate entropy (ApEn) approach to analyze randomness and the Detrended Fluctuation Analysis (DFA) to investigate the existence of long memory in α-HL channel kinetics. Single-channel currents were measured through experiments with α-HL channels incorporated in planar lipid bilayers. All experiments were carried out under the following conditions: 1 M NaCl solution, pH 4.5; transmembrane potential of + 40 mV and temperature 25 ± 1 °C. Single-channel currents were recorded in real-time in the memory of a microcomputer coupled to an A/D converter and a patch-clamp amplifier. The conductance value of the α-HL channels was 0.82 ± 0.0025 nS (n = 128). The DFA analysis showed that the kinetics of α-HL channels presents long-term memory ([Formula: see text] = 0.63 ± 0.04). The ApEn outcomes showed low complexity to dwell times when open (ApEno = 0.5514 ± 0.28) and closed (ApEnc = 0.1145 ± 0.08), corroborating the results of the DFA method.
Collapse
Affiliation(s)
- M P Silva
- Department of Animal Morphology and Physiology, Federal Rural University of Pernambuco, Recife, Pernambuco, Brazil
| | - C G Rodrigues
- Department of Biophysics and Radiobiology, Federal University of Pernambuco, Recife, Pernambuco, Brazil
| | - D C Machado
- Department of Biophysics and Radiobiology, Federal University of Pernambuco, Recife, Pernambuco, Brazil
| | - R A Nogueira
- Department of Animal Morphology and Physiology, Federal Rural University of Pernambuco, Recife, Pernambuco, Brazil.
| |
Collapse
|
3
|
Giugni FR, Dias RD, Rodrigues CG, Pinesi HT, Scalabrini-Neto A. Team emergency assessment measure (TEAM) of non-technical skills: The Brazilian Portuguese version of the TEAM tool. Clinics (Sao Paulo) 2022; 77:100043. [PMID: 35523106 PMCID: PMC9079709 DOI: 10.1016/j.clinsp.2022.100043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Accepted: 03/15/2022] [Indexed: 11/28/2022] Open
Abstract
OBJECTIVES The aim of this study was to conduct the translation and cross-cultural adaptation of the original Team Emergency Assessment Measure (TEAM) tool into the Brazilian Portuguese language and investigate the internal consistency, inter-rater reliability, and concurrent validity of this new version (bp-TEAM). METHODS Independent medical translators performed forward and backward translations of the TEAM tool between English and Portuguese, creating the bp-TEAM. The authors selected 23 videos from final-year medical students during in-situ emergency simulations. Three independent raters assessed all the videos using the bp-TEAM and provided a score for each of the 12 items of the tool. The authors assessed the internal consistency and the inter-rater reliability of the tool. RESULTS Raters assessed all 23 videos. Internal consistency was assessed among the 11 items of the bp-TEAM from one rater, yielding a Cronbach's alpha of 0.89. inter-item correlation analysis yielded a mean correlation coefficient rho of 0.46. Inter-rater reliability analysis among the three raters yielded an intraclass correlation coefficient of 0.86 (95% CI 0.83‒0.89), p < 0.001. CONCLUSION The Brazilian Portuguese version of the TEAM tool presented acceptable psychometric properties, similar to the original English version.
Collapse
Affiliation(s)
- Fernando Rabioglio Giugni
- Pathology Department, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo (HCFMUSP), São Paulo, SP, Brazil
| | - Roger Daglius Dias
- Department of Emergency Medicine, Harvard Medical School, Boston, MA, USA; STRATUS Center for Medical Simulation, Brigham and Women's Hospital, Harvard Medical School, Boston, USA.
| | - Caio Godoy Rodrigues
- Discipline of Clinical Emergencies, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo (HCFMUSP), São Paulo, SP, Brazil
| | - Henrique Trombini Pinesi
- Heart Institute, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo (HCFMUSP), São Paulo, SP, Brazil
| | - Augusto Scalabrini-Neto
- Discipline of Clinical Emergencies, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo (HCFMUSP), São Paulo, SP, Brazil; Abilities and Simulation Laboratory, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo (HCFMUSP), São Paulo, SP, Brazil
| |
Collapse
|
4
|
Abstract
Ion channels are transport proteins present in the lipid bilayers of biological membranes. They are involved in many physiological processes, such as the generation of nerve impulses, hormonal secretion, and heartbeat. Conformational changes in the ion channel-forming protein allow the opening or closing of pores to control the ionic flux through the cell membranes. The opening and closing of the ion channel have been classically treated as a random kinetic process, known as a Markov process. Here the time the channel remains in a given state is assumed to be independent of the condition it had in the previous state. More recently, however, several studies have shown that this process is not random but a deterministic one, where both the open and closed dwell-times and the ionic current flowing through the channel are history-dependent. This property is called long memory or long-range correlation. However, there is still much controversy regarding how this memory originates, which region of the channel is responsible for this property, and which models could best reproduce the memory effect. In this article, we provide a review of what is, where it is, its possible origin, and the mathematical methods used to analyze the long-term memory present in the kinetic process of ion channels.
Collapse
Affiliation(s)
- M P Silva
- Department of Animal Morphology and Physiology, Federal Rural University of Pernambuco, Recife, Pernambuco, Brazil
| | - C G Rodrigues
- Department of Biophysics and Radiobiology, Federal University of Pernambuco, Recife, Pernambuco, Brazil
| | - W A Varanda
- Department of Physiology-Faculty of Medicine of Ribeirão Preto, University of São Paulo (Retired), Ribeirão Preto, São Paulo, Brazil
| | - R A Nogueira
- Department of Animal Morphology and Physiology, Federal Rural University of Pernambuco, Recife, Pernambuco, Brazil.
| |
Collapse
|
5
|
Silva PM, Silva JNO, Silva BR, Ferreira GRS, Gaião WDC, Recio MV, Gonçalves GGA, Rodrigues CG, Medeiros PL, Brayner FA, Alves LC, Larsen MH, Ingmer H, Napoleão TH, Paiva PMG. Antibacterial effects of the lectin from pomegranate sarcotesta (PgTeL) against Listeria monocytogenes. J Appl Microbiol 2021; 131:671-681. [PMID: 33342053 DOI: 10.1111/jam.14978] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 12/14/2020] [Accepted: 12/17/2020] [Indexed: 12/18/2022]
Abstract
AIMS To investigate the effects of the lectin from Punica granatum sarcotesta (PgTeL) on growth, viability, cell structure, biofilm formation and chitinase activity of Listeria monocytogenes. In addition, the effect of PgTeL on the adhesion and invasion of human cells (HeLa) was determined. METHODS AND RESULTS PgTeL showed bacteriostatic and bactericidal effects on the strains L. monocytogenes N53-1 and EGD-e, causing morphometric alterations, cell aggregation, strong deformation and cell disruption. PgTeL inhibited biofilm formation by EGD-e and N53-1 and also interfered with the adhesion and invasion processes of EGD-e and N53-1 in HeLa cells. Finally, the chitinase activity of L. monocytogenes EGD-e was reduced in the presence of PgTeL, which can be involved in the inhibition of adhesion process. CONCLUSION PgTeL is an antibacterial agent against L. monocytogenes, inhibiting growth and promoting cell death, as well as impairing biofilm formation and bacterial adhesion and invasion into human cells. SIGNIFICANCE AND IMPACT OF THE STUDY The results stimulate future investigations on the potential of PgTeL for protection of contamination in food products.
Collapse
Affiliation(s)
- P M Silva
- Departamento de Bioquímica, Centro de Biociências, Universidade Federal de Pernambuco, Recife, Brazil
| | - J N O Silva
- Departamento de Bioquímica, Centro de Biociências, Universidade Federal de Pernambuco, Recife, Brazil
| | - B R Silva
- Departamento de Bioquímica, Centro de Biociências, Universidade Federal de Pernambuco, Recife, Brazil
| | - G R S Ferreira
- Departamento de Bioquímica, Centro de Biociências, Universidade Federal de Pernambuco, Recife, Brazil
| | - W D C Gaião
- Departamento de Biofísica e Radiobiologia, Centro de Biociências, Universidade Federal de Pernambuco, Recife, Brazil
| | - M V Recio
- Department of Veterinary and Animal Sciences, University of Copenhagen, Copenhagen, Denmark
| | - G G A Gonçalves
- Laboratório de Imunopatologia Keizo Asami, Universidade Federal de Pernambuco, Recife, Brazil.,Departamento de Parasitologia, Instituto Aggeu Magalhães, Fundação Oswaldo Cruz, Recife, Brazil
| | - C G Rodrigues
- Departamento de Biofísica e Radiobiologia, Centro de Biociências, Universidade Federal de Pernambuco, Recife, Brazil
| | - P L Medeiros
- Departamento de Histologia e Embriologia, Centro de Biociências, Universidade Federal de Pernambuco, Recife, Brazil
| | - F A Brayner
- Laboratório de Imunopatologia Keizo Asami, Universidade Federal de Pernambuco, Recife, Brazil.,Departamento de Parasitologia, Instituto Aggeu Magalhães, Fundação Oswaldo Cruz, Recife, Brazil
| | - L C Alves
- Laboratório de Imunopatologia Keizo Asami, Universidade Federal de Pernambuco, Recife, Brazil.,Departamento de Parasitologia, Instituto Aggeu Magalhães, Fundação Oswaldo Cruz, Recife, Brazil
| | - M H Larsen
- Department of Veterinary and Animal Sciences, University of Copenhagen, Copenhagen, Denmark
| | - H Ingmer
- Department of Veterinary and Animal Sciences, University of Copenhagen, Copenhagen, Denmark
| | - T H Napoleão
- Departamento de Bioquímica, Centro de Biociências, Universidade Federal de Pernambuco, Recife, Brazil
| | - P M G Paiva
- Departamento de Bioquímica, Centro de Biociências, Universidade Federal de Pernambuco, Recife, Brazil
| |
Collapse
|
6
|
Rodrigues CG, Rays J, Kanegae MY. Native-valve endocarditis caused by Achromobacter xylosoxidans: a case report and review of literature. Autops Case Rep 2017; 7:50-55. [PMID: 29043211 PMCID: PMC5634435 DOI: 10.4322/acr.2017.029] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Accepted: 06/12/2017] [Indexed: 11/29/2022]
Abstract
Achromobacter xylosoxidans is a Gram-negative aerobic bacterium first described by Yabuuchi and Ohyama in 1971. A. xylosoxidans is frequently found in aquatic environments. Abdominal, urinary tract, ocular, pneumonia, meningitis, and osteomyelitis are the most common infections. Infective endocarditis is rare. As far as we know, until now, only 19 cases have been described, including this current report. We report the case of community-acquired native valve endocarditis caused by A. xylosoxidans in an elderly patient without a concomitant diagnosis of a malignancy or any known immunodeficiency. The patient presented with a 2-month history of fever, weight loss, and progressive dyspnea. On physical examination, mitral and aortic murmurs were present, along with Janeway's lesions, and a positive blood culture for A. xylosoxidans. The transesophageal echocardiogram showed vegetation in the aortic valve, which was consistent with the diagnosis of infective endocarditis.
Collapse
Affiliation(s)
- Caio Godoy Rodrigues
- University of São Paulo (USP), School of Medicine, Internal Medicine Department. São Paulo, SP, Brazil
| | - Jairo Rays
- University of São Paulo (USP), Hospital Universitário, Internal Medicine Division. São Paulo, SP, Brazil
| | - Marcia Yoshie Kanegae
- University of São Paulo (USP), Hospital Universitário, Internal Medicine Division. São Paulo, SP, Brazil
| |
Collapse
|
7
|
Rodrigues CG, Pontes JM, Pignatelli N, Nunes V, Deus JR. Intermittent abdominal pain due to pancreatic pseudocyst hemorrhage diagnosed by endoscopic ultrasound. Endoscopy 2014; 45 Suppl 2 UCTN:E367-8. [PMID: 24285051 DOI: 10.1055/s-0033-1344769] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Affiliation(s)
- C G Rodrigues
- Hospital Fernando Fonseca - Gastroenterology, Amadora, Portugal
| | | | | | | | | |
Collapse
|
8
|
Fragoso AS, Silva MB, de Melo CP, Aguiar JLA, Rodrigues CG, de Medeiros PL, Branco Junior JF, Andrade CAS, Oliveira MDL. Dielectric study of the adhesion of mesenchymal stem cells from human umbilical cord on a sugarcane biopolymer. J Mater Sci Mater Med 2014; 25:229-237. [PMID: 24072391 DOI: 10.1007/s10856-013-5056-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Accepted: 09/16/2013] [Indexed: 06/02/2023]
Abstract
It is of current interest the identification of appropriate matrices for growing mesenchymal stem cells (MSC). These cells are able not only to regenerate themselves but also to differentiate into other type of functional cells, and so they have been extensively used in tissue engineering. In this work, we have evaluated the use of electric impedance spectroscopy (EIS) to follow the adhesion of MSC from Wharton's jelly of the human umbilical cord (hWJMSC) on sugarcane biopolymers (SCB). Impedance spectra of the systems were obtained in the frequency range of 10(2)-10(5) Hz. An EIS investigation showed that when deposited on a metallic electrode SCB films prevent the passage of electrons between the solution and the metallic interface. The impedance spectra of hWJMSCs adhered on SCB revealed that there is a significant increase in the magnitude of the impedance when compared to that of pure SCB. The corresponding resistance (real part of the impedance) was even higher for the SCB-hWJMSC system than for SCB without cells on their surface, in an indication of an increased blockage to the electron transfers. The resistance charge transfer is extracted by curve-fitting the impedance spectra to an equivalent circuit model. Also, a shift of the phase angle to higher frequencies was obtained for SCB-hWJMSC system as a result from hWJMSC adhesion. Our study demonstrates that EIS is an appropriate method to evaluate the adhesion of MSC. SCB can be considered as a promising biomaterial for tissue engineering.
Collapse
Affiliation(s)
- A S Fragoso
- Programa de Pós-Graduação em Ciências Biológicas, Universidade Federal de Pernambuco, Recife, PE, 50670-901, Brazil
| | | | | | | | | | | | | | | | | |
Collapse
|
9
|
da Silva MB, Costa VMA, Pereira VRA, de Albertim GJB, de Melo EBB, Bezerra DP, da Silva RP, Rodrigues CG, Carneiro CMM, Yuldasheva LN, Krasilnikov OV. Ion channels in volume regulation of clonal kidney cells. Cell Prolif 2010; 43:529-41. [PMID: 21039991 DOI: 10.1111/j.1365-2184.2010.00702.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
OBJECTIVES Clonal kidney cells (Vero cells) are extensively utilized in the manufacture of biological preparations for disease diagnostics and therapeutics and also in preparation of vaccines. In all cells, regulation of volume is an essential function coupled to a variety of physiological processes and is a topic of interest. The objective here was to investigate involvement of ion channels in the process of volume regulation of Vero cells. METHODS Involvement of ion channels in cell volume regulation was studied using video-microscopy and flow cytometry. Pharmacologically unaltered cells of different sizes, which are presumably at different phases of the cell cycle, were used. RESULTS Ion transport inhibitors altered all phases of regulatory volume decrease (RVD) of Vero cells, rate of initial cell swelling, V(max) and volume recovery. Effects were dependent on type of inhibitor and on cell size (cell cycle phase). Participation of aquaporins in RVD was suggested. Inhibitors decelerated growth, arresting Vero cells at the G(0) /G(1) phase boundary. Electrophysiological study confirmed presence of volume-activated Cl(-) channels and K(+) channels in plasmatic membranes of the cells. CONCLUSION Vero cells of all sizes maintained the ability to recover from osmotic swelling. Activity of ion channels was one of the key factors that controlled volume regulation and proliferation of the cells.
Collapse
Affiliation(s)
- M B da Silva
- Department of Biophysics and Radiobiology, Federal University of Pernambuco, Recife, PE, Brazil
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
10
|
Rodrigues CG, Alberto SF, Felix J, Pires E, de Deus JR. Argon plasma coagulation treatment in patients with chronic radiation proctitis. Endoscopy 2010; 42:518; author reply 519. [PMID: 20506070 DOI: 10.1055/s-0029-1244109] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
|
11
|
Yuldasheva LN, Merzlyak PG, Zitzer AO, Rodrigues CG, Bhakdi S, Krasilnikov OV. Lumen geometry of ion channels formed by Vibrio cholerae EL Tor cytolysin elucidated by nonelectrolyte exclusion. Biochim Biophys Acta 2001; 1512:53-63. [PMID: 11334624 DOI: 10.1016/s0005-2736(01)00302-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Vibrio cholerae EL Tor cytolysin, a water-soluble protein with a molecular mass of 63 kDa, forms small pores in target cell membranes. In this communication, planar lipid bilayers under voltage clamp conditions were used to investigate the geometric properties of the pores. It was established that all cytolysin channels were inserted into membranes with the same orientation. Sharp asymmetry in the I-V curve of fully open cytolysin channels persisting at high electrolyte concentrations indicated asymmetry in the geometry of the channel lumen. Using the nonelectrolyte exclusion method, evidence was obtained that the cis opening of the channel had a larger diameter (< or = 1.9 nm) than the trans opening (< or = 1.6 nm). The channel lumen appeared constricted, with a diameter of < or = 1.2 nm. Cup-shaped lumen geometry was deduced for both channel openings, which appeared to be connected to each other via a central narrow part. The latter contributed significantly to the total electrical resistance and determined the discontinuous character of channel filling with nonelectrolytes. Comparisons of the properties of pores formed by cytolysins of two V. cholerae biotypes (EL Tor and non-O1) indicated that the two ion channels possessed a similar geometry.
Collapse
Affiliation(s)
- L N Yuldasheva
- Laboratory of Membrane Biophysics, Center of Biological Sciences, Department of Biophysics and Radiobiology, Federal University of Pernambuco, Recife, PE, Brazil
| | | | | | | | | | | |
Collapse
|
12
|
Krasilnikov OV, Merzlyak PG, Yuldasheva LN, Rodrigues CG, Bhakdi S, Valeva A. Electrophysiological evidence for heptameric stoichiometry of ion channels formed by Staphylococcus aureus alpha-toxin in planar lipid bilayers. Mol Microbiol 2000; 37:1372-8. [PMID: 10998169 DOI: 10.1046/j.1365-2958.2000.02080.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Staphylococcal alpha-toxin forms homo-oligomeric channels in lipid bilayers and cell membranes. Here, we report that electrophysiological monitoring of single-channel function using a derivatized cysteine substitution mutant allows accurate determination of the subunit stoichiometry of the oligomer in situ. The electrophysiological phenotype of channels formed in planar lipid bilayers with the cysteine replacement mutant I7C is equal to that of the wild type. When pores were formed with I7C, alterations of several channel properties were observed upon modification with SH reagents. Decreases in conductance then occurred that were seen only as negative voltage was applied. At the level of single channels, these were manifest as stepwise changes in conductance, each step most probably reflecting modification of a single SH group within the oligomer. Because seven steps were observed, the functional channel formed by alpha-toxin in planar lipid membranes is a heptamer.
Collapse
Affiliation(s)
- O V Krasilnikov
- Laboratory of Membrane Biophysics, Department of Biophysics and Radiobiology, Federal University of Pernambuco, 50670-901, Recife, PE, Brazil.
| | | | | | | | | | | |
Collapse
|
13
|
Merzlyak PG, Yuldasheva LN, Rodrigues CG, Carneiro CM, Krasilnikov OV, Bezrukov SM. Polymeric nonelectrolytes to probe pore geometry: application to the alpha-toxin transmembrane channel. Biophys J 1999; 77:3023-33. [PMID: 10585924 PMCID: PMC1300573 DOI: 10.1016/s0006-3495(99)77133-x] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Asymmetrical (one-sided) application of penetrating water-soluble polymers, polyethylene glycols (PEGs), to a well-defined channel formed by Staphylococcus aureus alpha-toxin is shown to probe channel pore geometry in more detail than their symmetrical (two-sided) application. Polymers added to the cis side of the planar lipid membrane (the side of protein addition) affect channel conductance differently than polymers added to the trans side. Because a satisfactory theory quantitatively describing PEG partitioning into a channel pore does not exist, we apply the simple empirical rules proposed previously (, J. Membr. Biol. 161:83-92) to gauge the size of pore openings as well as the size and position of constrictions along the pore axis. We estimate the radii of the two openings of the channel to be practically identical and equal to 1. 2-1.3 nm. Two apparent constrictions with radii of approximately 0. 9 nm and approximately 0.6-0.7 nm are inferred to be present in the channel lumen, the larger one being closer to the cis side. These structural findings agree well with crystallographic data on the channel structure (, Science. 274:1859-1866) and verify the practicality of polymer probing. The general features of PEG partitioning are examined using available theoretical considerations, assuming there is no attraction between PEG and the channel lumen. It is shown that the sharp dependence of the partition coefficient on polymer molecular weight found under both symmetrical and asymmetrical polymer application can be rationalized within a "hard sphere nonideal solution model." This finding is rather surprising because PEG forms highly flexible coils in water with a Kuhn length of only several Angstroms.
Collapse
Affiliation(s)
- P G Merzlyak
- Laboratory of Membrane Biophysics, Department of Biophysics and Radiobiology, Federal University of Pernambuco, 50670-901, Recife, PE, Brazil
| | | | | | | | | | | |
Collapse
|
14
|
Krasilnikov OV, Merzlyak PG, Yuldasheva LN, Rodrigues CG, Nogueira RA. Heparin influence on alpha-staphylotoxin formed channel. Biochim Biophys Acta 1999; 1417:167-82. [PMID: 10076045 DOI: 10.1016/s0005-2736(98)00244-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The effects of heparin on ion channels formed by Staphylococcus aureus alpha-toxin (ST channel) in lipid bilayers were studied under voltage clamp conditions. Heparin concentrations as small as 100 pM induced a sharp dose-dependent increase in channel voltage sensitivity. This was only observed when heparin was added to the negative-potential side of lipid bilayers in the presence of divalent cations. Divalent cations differ in their efficiency: Zn2+>Ca2+>Mg2+. The apparent positive gating charge increased 2-3-fold with heparin addition as well as with acidification of the bathing solution. 'Free' carboxyl groups and carboxyl groups in ion pairs of the protein moiety are hypothesized to interact with sulfated groups of heparin through divalent cation bridges. The cis mouth of the channel (that protrudes beyond the membrane plane on the side of ST addition and to which voltage was applied) is less sensitive to heparin than the trans-mouth. It is suggested that charged residues which interact with heparin at the cis mouth of ST channels and which contribute to the effective gating charge at negative voltage may be physically different from those at the trans mouth and at positive voltage.
Collapse
Affiliation(s)
- O V Krasilnikov
- Laboratory of Molecular Physiology, Institute of Physiology and Biophysics, 700095, Tashkent, Uzbekistan.
| | | | | | | | | |
Collapse
|
15
|
Krasilnikov OV, Yuldasheva LN, Nogueira RA, Rodrigues CG. The diameter of water pores formed by colicin Ia in planar lipid bilayers. Braz J Med Biol Res 1995; 28:693-8. [PMID: 8547854] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The effective size of colicin Ia channel was tested by a recently described method (FEMS, Microbiology and Immunology (1992). 105: 93-100) in which the nonelectrolyte molecules with different hydrodynamic diameters (0.52 to 5.0 nm) were used as molecular tools. We have shown that despite low conductance (55-105 pS at 1.5 M KCl, pH 7.0) the ion channels formed by colicin Ia have a fairly large water pore diameter equal to 1.66-1.88 nm. The results are discussed in terms of an energetic barrier for ions passing into the channel lumen.
Collapse
Affiliation(s)
- O V Krasilnikov
- Laboratory of Molecular Physiology, Institute of Physiology and Biophysics, Tashkent, Uzbekistan
| | | | | | | |
Collapse
|
16
|
Krasilnikov OV, Merzliak PG, Yuldasheva LN, Nogueira RA, Rodrigues CG. Non stochastic distribution of single channels in planar lipid bilayers. Biochim Biophys Acta 1995; 1233:105-10. [PMID: 7532434 DOI: 10.1016/0005-2736(94)00231-d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The selectivity of the planar lipid bilayers modified by two channel-forming proteins (alpha-toxin S. aureus and colicin Ia) was examined. It was established that in all cases the value of zero current potential depended on the amount of open ion channels and increased with the number of channels (from one to about 5-7). These facts point out both the interactions among ion channels and their non stochastic distribution on the membrane surface.
Collapse
Affiliation(s)
- O V Krasilnikov
- Laboratory of Molecular Physiology, Institute of Physiology and Biophysics, Tashkent, Uzbekistan
| | | | | | | | | |
Collapse
|
17
|
Chang TK, Iverson SA, Rodrigues CG, Kiser CN, Lew AY, Germanas JP, Richards JH. Gene synthesis, expression, and mutagenesis of the blue copper proteins azurin and plastocyanin. Proc Natl Acad Sci U S A 1991; 88:1325-9. [PMID: 1899926 PMCID: PMC51010 DOI: 10.1073/pnas.88.4.1325] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Genes for the blue copper proteins Populus nigra var. italica plastocyanin and Pseudomonas aeruginosa azurin have been constructed by a stepwise procedure. The leader sequence for azurin has been placed before the genes directing plastocyanin and azurin transport to the periplasmic space when the genes are expressed in Escherichia coli. Site-saturation mutagenesis has been used to alter two copper-binding residues of azurin (Met-121 and His-46) and Met-92 of plastocyanin. While the plastocyanin mutants do not appear to bind copper, the azurin variants all bind copper and show characteristic type I blue copper centers. In particular, the electronic spectra reflect the dominance of the charge transfer interaction between copper and the thiolate of Cys-112, being relatively insensitive to changes in Met-121 or His-46. In contrast, removal of Met-121 appreciably alters the EPR spectra of the mutants, although, to a first order, the spectra of all mutants are themselves similar, suggesting a more distorted geometry around copper in the mutants than in the wild type.
Collapse
Affiliation(s)
- T K Chang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena 91125
| | | | | | | | | | | | | |
Collapse
|