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1.
Geburtshilfe Frauenheilkd ; 84(2): 153-163, 2024 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-38344046

RESUMO

Introduction: Certified breast cancer centers offer specific quality standards in terms of their structure, diagnostic and treatment approaches with regards to breast surgery, drug-based cancer therapy, radiotherapy, and psychosocial support. Such centers aim to improve treatment outcomes of breast cancer patients. The question investigated here was whether patients with primary breast cancer have a longer overall survival if they are treated in a certified breast cancer center compared to treatment outside these centers. Methods: We used patient-specific data (demographics, diagnoses, treatments) obtained from data held by mandatory health insurance companies ( gesetzliche Krankenversicherung , GKV) and clinical cancer registries (KKR) for the period 2009-2017 as well as hospital characteristics recorded in standardized quality reports. Using multivariable Cox regression analysis, we investigated differences in survival between patients treated in hospitals certified as breast cancers centers by the German Cancer Society (DKG) and patients treated in hospitals which had not been certified by the DKG. Results: The sample population consisted of 143720 (GKV data) and 59780 (KKR data) patients with breast cancer, who were treated in 1010 hospitals across Germany (280 DKG-certified, 730 not DKG-certified). 63.5% (GKV data) and 66.7% (KKR data) of patients, respectively, were treated in DKG-certified breast cancer centers. Cox regression analysis for overall survival which included patient and hospital characteristics found a significantly lower mortality risk for patients treated in DKG-certified breast cancer centers (GKV data: HR = 0.77, 95% CI = 0.74-0.81; KKR data: HR = 0.88, 95% CI = 0.85-0.92). This result remained stable even after several sensitivity analyses including stratified estimates for subgroups of patients and hospitals. The effect was even more pronounced for recurrence-free survival (KKR data: HR = 0.78, 95% CI = 0.74-0.82). Conclusions: Patients who are treated by an interdisciplinary team in a DKG-certified breast cancer had clear and statistically significantly better survival rates. Certification is therefore an effective means of improving the quality of care, and more patients should be treated in certified breast cancer centers.

2.
PLoS One ; 19(1): e0297039, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38295046

RESUMO

BACKGROUND: The COVID-19 pandemic revealed a need for better collaboration among research, care, and management in Germany as well as globally. Initially, there was a high demand for broad data collection across Germany, but as the pandemic evolved, localized data became increasingly necessary. Customized dashboards and tools were rapidly developed to provide timely and accurate information. In Saxony, the DISPENSE project was created to predict short-term hospital bed capacity demands, and while it was successful, continuous adjustments and the initial monolithic system architecture of the application made it difficult to customize and scale. METHODS: To analyze the current state of the DISPENSE tool, we conducted an in-depth analysis of the data processing steps and identified data flows underlying users' metrics and dashboards. We also conducted a workshop to understand the different views and constraints of specific user groups, and brought together and clustered the information according to content-related service areas to determine functionality-related service groups. Based on this analysis, we developed a concept for the system architecture, modularized the main services by assigning specialized applications and integrated them into the existing system, allowing for self-service reporting and evaluation of the expert groups' needs. RESULTS: We analyzed the applications' dataflow and identified specific user groups. The functionalities of the monolithic application were divided into specific service groups for data processing, data storage, predictions, content visualization, and user management. After composition and implementation, we evaluated the new system architecture against the initial requirements by enabling self-service reporting to the users. DISCUSSION: By modularizing the monolithic application and creating a more flexible system, the challenges of rapidly changing requirements, growing need for information, and high administrative efforts were addressed. CONCLUSION: We demonstrated an improved adaptation towards the needs of various user groups, increased efficiency, and reduced burden on administrators, while also enabling self-service functionalities and specialization of single applications on individual service groups.


Assuntos
Armazenamento e Recuperação da Informação , Pandemias , Humanos , Coleta de Dados , Alemanha
3.
World J Surg Oncol ; 22(1): 11, 2024 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-38183134

RESUMO

BACKGROUND: Certified cancer centers aim to ensure high-quality care by establishing structural and procedural standards according to evidence-based guidelines. Despite the high clinical and health policy relevance, evidence from a nation-wide study for the effectiveness of care for colorectal cancer in certified centers vs. other hospitals in Germany is still missing. METHODS: In a retrospective cohort study covering the years 2009-2017, we analyzed patient data using demographic information, diagnoses, and treatments from a nationwide statutory health insurance enriched with information on certification. We investigated whether patients with incident colon or rectal cancer did benefit from primary therapy in a certified cancer center. We used relative survival analysis taking into account mortality data of the German population and adjustment for patient and hospital characteristics via Cox regression with shared frailty for patients in hospitals with and without certification. RESULTS: The cohorts for colon and rectal cancer consisted of 109,518 and 51,417 patients, respectively, treated in a total of 1052 hospitals. 37.2% of patients with colon and 42.9% of patients with rectal cancer were treated in a certified center. Patient age, sex, comorbidities, secondary malignoma, and distant metastases were similar across groups (certified/non-certified) for both colon and rectal cancer. Relative survival analysis showed significantly better survival of patients treated in a certified center, with 68.3% (non-certified hospitals 65.8%) 5-year survival for treatment of colon cancer in certified (p < 0.001) and 65.0% (58.8%) 5-year survival in case of rectal cancer (p < 0.001), respectively. Cox regression with adjustment for relevant covariates yielded a lower hazard of death for patients treated in certified centers for both colon (HR = 0.92, 95% CI = 0.89-0.95) and rectal cancer (HR = 0.92, 95% CI = 0.88-0.95). The results remained robust in a series of sensitivity analyses. CONCLUSIONS: This large cohort study yields new important evidence that patients with colorectal cancer have a better chance of survival if treated in a certified cancer center. Certification thus provides one powerful means to improve the quality of care for colorectal cancer. To decrease the burden of disease, more patients should thus receive cancer care in a certified center.


Assuntos
Neoplasias Retais , Humanos , Estudos de Coortes , Estudos Retrospectivos , Neoplasias Retais/terapia , Certificação , Colo
4.
Cancers (Basel) ; 15(18)2023 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-37760537

RESUMO

(1) Background: The WiZen study is the largest study so far to analyze the effect of the certification of designated cancer centers on survival in Germany. This certification program is provided by the German Cancer Society (GCS) and represents one of the largest oncologic certification programs worldwide. Currently, about 50% of colorectal cancer patients in Germany are treated in certified centers. (2) Methods: All analyses are based on population-based clinical cancer registry data of 47.440 colorectal cancer (ICD-10-GM C18/C20) patients treated between 2009 and 2017. The primary outcome was 5-year overall survival (OAS) after treatment at certified cancer centers compared to treatment at other hospitals; the secondary endpoint was recurrence-free survival. Statistical methods included Kaplan-Meier analysis and multivariable Cox regression. (3) Results: Treatment at certified hospitals was associated with significant advantages concerning 5-year overall survival (HR 0.92, 95% CI 0.89, 0.96, adjusted for a broad range of confounders) for colon cancer patients. Concentrating on UICC stage I-III patients, for whom curative treatment is possible, the survival benefit was even larger (colon cancer: HR 0.89, 95% CI 0.84, 0.94; rectum cancer: HR 0.91, 95% CI 0.84, 0.97). (4) Conclusions: These results encourage future efforts for further implementation of the certification program. Patients with colorectal cancer should preferably be directed to certified centers.

5.
Gesundheitswesen ; 85(S 03): S197-S204, 2023 Sep.
Artigo em Inglês, Alemão | MEDLINE | ID: mdl-37751756

RESUMO

BACKGROUND: Certification programs seek to improve the quality of complex interdisciplinary models of care such as cancer treatment through structuring the process of care in accordance with evidence-based guidelines. In Germany, the German Cancer Society (Deutsche Krebsgesellschaft, DKG) provides a certification programme for cancer care that covers more than one thousand centers. In a recent retrospective cohort study, it has been shown on a large, nationwide data set based on data from a statutory health insurance and selected clinical cancer registries, that there is a benefit in survival for cancer patients who have received initial treatment in hospitals certified by the DKG. Here, we deduce two absolute measures from the relative benefit in survival with the aim to quantify this benefit if all patients had been treated in a certified center. METHODS: The WiZen study analysed survival of adult patients insured by the AOK with a cancer diagnosis between 2009 and 2017 in certified hospitals vs. non-certified hospitals. Besides Kaplan-Meier-estimators, Cox regression with shared frailty was used for 11 types of cancer in total, adjusting for patient-specific information such as demographic characteristics and comorbidities as well as hospital characteristics and temporal trend. Based on this regression, we predict adjusted survival curves that directly address the certification effect. From the adjusted survivals, we calculated years of life lost (YLL) and number needed to treat (NNT), along with a difference in deaths 5 years after diagnosis. RESULTS: Based on our estimate for the 537,396 patients that were treated in a non-certified hospital included in the WiZen study, corresponding to 68,7% of the study population, we find a potential of 33,243 YLL per year in Germany based on the size of the German population as of 2017. The potential to avoid death cases 5 years from diagnosis totals 4,729 per year in Germany. CONCLUSION: While Cox regression is an important tool to evaluate the benefit that arises from variables with a potential impact on survival such as certification, its direct results are not well suited to quantify this benefit for decision makers in health care. The estimated years of life lost and the number of deaths that could have been avoided 5 years from diagnosis avoid mis-interpretation of the hazard ratios commonly used in survival analysis and should help to inform key stakeholders in health care without specialist background knowledge in statistics. Our measures, directly adressing the effect of certification, can furthermore be used as a starting point for health-economic calculations. Steering the care of cancer patients primarily to certified hospitals would have a high potential to improve outcomes.


Assuntos
Certificação , Neoplasias , Adulto , Humanos , Estudos Retrospectivos , Alemanha/epidemiologia , Neoplasias/diagnóstico , Neoplasias/terapia , Hospitais , Análise de Sobrevida
6.
Dtsch Arztebl Int ; 120(39): 647-654, 2023 09 29.
Artigo em Inglês | MEDLINE | ID: mdl-37583089

RESUMO

BACKGROUND: According to the National Cancer Plan in Germany, all cancer patients should receive high-quality care in accordance with evidence-based treatment guidelines. Certification programs were established for this purpose but have not yet been comprehensively evaluated. METHODS: In the WiZen project, which was supported by the Innovation Fund (supported project number 01VSF17020), controlled cohort studies were performed to investigate whether initial treatment in hospitals with or without a certificate from the German Cancer Society was associated with a difference in overall survival (primary endpoint) in patients with cancer of the colon, rectum, lung, pancreas, breast, cervix, prostate, endometrium, and ovary, head and neck cancer, and neuro-oncological tumors. The studies were based on nationwide data from adult insurees of the AOK statutory health insurance carrier for the years 2009-2017. RESULTS: The majority of patients with all entities except breast cancer received their initial treatment in non-certified hospitals. Initial treatment in a certified hospital was found to be beneficial in terms of overall survival for all cancer entities, even after extensive adjustment for patient- and hospital-related confounders. The hazard ratio (HR) ranged from 0.97 (95% CI: [0.94; 1.00]) for lung cancer to 0.77 [0.74; 0.81] for breast cancer, corresponding to an absolute risk reduction (ARR) for overall survival of 0.62 months for lung cancer to 4.61 months for cervical cancer. CONCLUSION: The WiZen study shows for the entities studied that initial cancer treatment in a certified center is associated with lower mortality. Despite the recommendations of the National Cancer Plan, however, more than 40% of all cancer patients still receive their initial treatment in a non-certified hospital. The preferential provision of initial care in certified hospitals would be likely to improve overall survival. Although the study design does not permit any conclusion with regard to causality, the findings seem robust considering that a control group was used, confounders were taken into account, and the study population was of large size.


Assuntos
Neoplasias da Mama , Neoplasias de Cabeça e Pescoço , Neoplasias Pulmonares , Masculino , Adulto , Feminino , Humanos , Hospitais , Neoplasias da Mama/terapia , Alemanha/epidemiologia , Certificação
7.
Gesundheitswesen ; 85(S 02): S154-S161, 2023 Mar.
Artigo em Alemão | MEDLINE | ID: mdl-36940697

RESUMO

BACKGROUND: The aim of the project "Effectiveness of care in oncological centres" (WiZen), funded by the innovation fund of the federal joint committee, is to investigate the effectiveness of certification in oncology. The project uses nationwide data from the statuory health insurance AOK and data from clinical cancer registries from three different federal states from 2006-2017. To combine the strengths of both data sources, these will be linked for eight different cancer entities in compliance with data protection regulations. METHODS: Data linkage was performed using indirect identifiers and validated using the health insurance's patient ID ("Krankenversichertennummer") as a direct identifier and gold standard. This enables quantification of the quality of different linkage variants. Sensitivity and specificity as well as hit accuracy and a score addressing the quality of the linkage were used as evaluation criteria. The distributions of relevant variables resulting from the linkage were validated against the original distributions in the individual datasets. RESULTS: Depending on the combination of indirect identifiers, we found a range of 22,125 to 3,092,401 linkage hits. An almost perfect linkage could be achieved by combining information on cancer type, date of birth, gender and postal code. A total of 74,586 one-to-one linkages were achieved with these characteristics. The median hit quality for the different entities was more than 98%. In addition, both the age and sex distributions and the dates of death, if any, showed a high degree of agreement. DISCUSSION AND CONCLUSION: SHI and cancer registry data can be linked with high internal and external validity at the individual level. This robust linkage enables completely new possibilities for analysis through simultaneous access to variables from both data sets ("the best of both worlds"): Information on the UICC stage that stems from the registries can now be combined, for instance, with comorbidities from the SHI data at the individual level. Due to the use of readily available variables and the high success of the linkage, our procedure constitutes a promising method for future linkage processes in health care research.


Assuntos
Neoplasias , Dados de Saúde Coletados Rotineiramente , Humanos , Alemanha/epidemiologia , Sistema de Registros , Armazenamento e Recuperação da Informação , Seguro Saúde , Neoplasias/epidemiologia , Registro Médico Coordenado/métodos
8.
BMC Cancer ; 22(1): 621, 2022 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-35672675

RESUMO

BACKGROUND: Treatment of cancer patients in certified cancer centers, that meet specific quality standards in term of structures and procedures of medical care, is a national treatment goal in Germany. However, convincing evidence that treatment in certified cancer centers is associated with better outcomes in patients with pancreatic cancer is still missing. METHODS: We used patient-specific information (demographic characteristics, diagnoses, treatments) from German statutory health insurance data covering the period 2009-2017 and hospital characteristics from the German Standardized Quality Reports. We investigated differences in survival between patients treated in hospitals with and without pancreatic cancer center certification by the German Cancer Society (GCS) using the Kaplan-Meier estimator and Cox regression with shared frailty. RESULTS: The final sample included 45,318 patients with pancreatic cancer treated in 1,051 hospitals (96 GCS-certified, 955 not GCS-certified). 5,426 (12.0%) of the patients were treated in GCS-certified pancreatic cancer centers. Patients treated in certified and non-certified hospitals had similar distributions of age, sex, and comorbidities. Median survival was 8.0 months in GCS-certified pancreatic cancer centers and 4.4 months in non-certified hospitals. Cox regression adjusting for multiple patient and hospital characteristics yielded a significantly lower hazard of long-term, all-cause mortality in patients treated in GCS-certified pancreatic centers (Hazard ratio = 0.89; 95%-CI = 0.85-0.93). This result remained robust in multiple sensitivity analyses, including stratified estimations for subgroups of patients and hospitals. CONCLUSION: This robust observational evidence suggests that patients with pancreatic cancer benefit from treatment in a certified cancer center in terms of survival. Therefore, the certification of hospitals appears to be a powerful strategy to improve patient outcomes in pancreatic cancer care. TRIAL REGISTRATION: ClinicalTrials.gov ( NCT04334239 ).


Assuntos
Certificação , Neoplasias Pancreáticas , Estudos de Coortes , Alemanha/epidemiologia , Hospitais , Humanos , Neoplasias Pancreáticas/terapia , Análise de Sobrevida
9.
PLoS One ; 17(1): e0262491, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35085297

RESUMO

As of late 2019, the COVID-19 pandemic has been a challenge to health care systems worldwide. Rapidly rising local COVID-19 incidence rates, result in demand for high hospital and intensive care bed capacities on short notice. A detailed up-to-date regional surveillance of the dynamics of the pandemic, precise prediction of required inpatient capacities of care as well as a centralized coordination of the distribution of regional patient fluxes is needed to ensure optimal patient care. In March 2020, the German federal state of Saxony established three COVID-19 coordination centers located at each of its maximum care hospitals, namely the University Hospitals Dresden and Leipzig and the hospital Chemnitz. Each center has coordinated inpatient care facilities for the three regions East, Northwest and Southwest Saxony with 36, 18 and 29 hospital sites, respectively. Fed by daily data flows from local public health authorities capturing the dynamics of the pandemic as well as daily reports on regional inpatient care capacities, we established the information and prognosis tool DISPENSE. It provides a regional overview of the current pandemic situation combined with daily prognoses for up to seven days as well as outlooks for up to 14 days of bed requirements. The prognosis precision varies from 21% and 38% to 12% and 15% relative errors in normal ward and ICU bed demand, respectively, depending on the considered time period. The deployment of DISPENSE has had a major positive impact to stay alert for the second wave of the COVID-19 pandemic and to allocate resources as needed. The application of a mathematical model to forecast required bed capacities enabled concerted actions for patient allocation and strategic planning. The ad-hoc implementation of these tools substantiates the need of a detailed data basis that enables appropriate responses, both on regional scales in terms of clinic resource planning and on larger scales concerning political reactions to pandemic situations.


Assuntos
Previsões/métodos , Hospitalização/tendências , Aceitação pelo Paciente de Cuidados de Saúde/estatística & dados numéricos , COVID-19/epidemiologia , Cuidados Críticos , Atenção à Saúde , Alemanha/epidemiologia , Hospitalização/estatística & dados numéricos , Humanos , Pacientes Internados , Unidades de Terapia Intensiva , Modelos Teóricos , Pandemias/estatística & dados numéricos , SARS-CoV-2/patogenicidade
10.
Curr Biol ; 27(9): 1314-1325, 2017 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-28457871

RESUMO

Navigation of cells along gradients of guidance cues is a determining step in many developmental and immunological processes. Gradients can either be soluble or immobilized to tissues as demonstrated for the haptotactic migration of dendritic cells (DCs) toward higher concentrations of immobilized chemokine CCL21. To elucidate how gradient characteristics govern cellular response patterns, we here introduce an in vitro system allowing to track migratory responses of DCs to precisely controlled immobilized gradients of CCL21. We find that haptotactic sensing depends on the absolute CCL21 concentration and local steepness of the gradient, consistent with a scenario where DC directionality is governed by the signal-to-noise ratio of CCL21 binding to the receptor CCR7. We find that the conditions for optimal DC guidance are perfectly provided by the CCL21 gradients we measure in vivo. Furthermore, we find that CCR7 signal termination by the G-protein-coupled receptor kinase 6 (GRK6) is crucial for haptotactic but dispensable for chemotactic CCL21 gradient sensing in vitro and confirm those observations in vivo. These findings suggest that stable, tissue-bound CCL21 gradients as sustainable "roads" ensure optimal guidance in vivo.


Assuntos
Quimiocina CCL21/metabolismo , Quimiotaxia , Células Dendríticas/metabolismo , Quinases de Receptores Acoplados a Proteína G/fisiologia , Receptores CCR7/metabolismo , Razão Sinal-Ruído , Animais , Rastreamento de Células , Células Dendríticas/citologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Transdução de Sinais
11.
Sci Rep ; 6: 36440, 2016 11 07.
Artigo em Inglês | MEDLINE | ID: mdl-27819270

RESUMO

Cellular locomotion is a central hallmark of eukaryotic life. It is governed by cell-extrinsic molecular factors, which can either emerge in the soluble phase or as immobilized, often adhesive ligands. To encode for direction, every cue must be present as a spatial or temporal gradient. Here, we developed a microfluidic chamber that allows measurement of cell migration in combined response to surface immobilized and soluble molecular gradients. As a proof of principle we study the response of dendritic cells to their major guidance cues, chemokines. The majority of data on chemokine gradient sensing is based on in vitro studies employing soluble gradients. Despite evidence suggesting that in vivo chemokines are often immobilized to sugar residues, limited information is available how cells respond to immobilized chemokines. We tracked migration of dendritic cells towards immobilized gradients of the chemokine CCL21 and varying superimposed soluble gradients of CCL19. Differential migratory patterns illustrate the potential of our setup to quantitatively study the competitive response to both types of gradients. Beyond chemokines our approach is broadly applicable to alternative systems of chemo- and haptotaxis such as cells migrating along gradients of adhesion receptor ligands vs. any soluble cue.


Assuntos
Quimiocina CCL19/farmacologia , Quimiocina CCL21/farmacologia , Quimiotaxia/efeitos dos fármacos , Células Dendríticas/fisiologia , Microfluídica/métodos , Animais , Células da Medula Óssea/citologia , Movimento Celular/efeitos dos fármacos , Células Cultivadas , Quimiocina CCL19/química , Quimiocina CCL19/metabolismo , Quimiocina CCL21/química , Células Dendríticas/citologia , Fluoresceína-5-Isotiocianato/química , Proteínas Imobilizadas/química , Proteínas Imobilizadas/metabolismo , Proteínas Imobilizadas/farmacologia , Dispositivos Lab-On-A-Chip , Camundongos , Camundongos Endogâmicos C57BL , Microfluídica/instrumentação , Microscopia de Fluorescência , Fotodegradação , Especificidade por Substrato
12.
Phys Biol ; 12(6): 066003, 2015 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-26403517

RESUMO

In growing cells, protein synthesis and cell growth are typically not synchronous, and, thus, protein concentrations vary over the cell division cycle. We have developed a theoretical description of genetic regulatory systems in bacteria that explicitly considers the cell division cycle to investigate its impact on gene expression. We calculate the cell-to-cell variations arising from cells being at different stages in the division cycle for unregulated genes and for basic regulatory mechanisms. These variations contribute to the extrinsic noise observed in single-cell experiments, and are most significant for proteins with short lifetimes. Negative autoregulation buffers against variation of protein concentration over the division cycle, but the effect is found to be relatively weak. Stronger buffering is achieved by an increased protein lifetime. Positive autoregulation can strongly amplify such variation if the parameters are set to values that lead to resonance-like behaviour. For cooperative positive autoregulation, the concentration variation over the division cycle diminishes the parameter region of bistability and modulates the switching times between the two stable states. The same effects are seen for a two-gene mutual-repression toggle switch. By contrast, an oscillatory circuit, the repressilator, is only weakly affected by the division cycle.


Assuntos
Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Ciclo Celular , Escherichia coli/citologia , Redes Reguladoras de Genes , Escherichia coli/genética , Escherichia coli/metabolismo , Modelos Genéticos , Biossíntese de Proteínas
13.
J Theor Biol ; 348: 1-11, 2014 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-24480713

RESUMO

Gene expression is an inherently noisy process. Fluctuations arise at many points in the expression of a gene, as all the salient reactions such as transcription, translation, and mRNA degradation are stochastic processes. The fluctuations become important when the cellular copy numbers of the relevant molecules (mRNA or proteins) are low. For regulated genes, a computational complication arises from the fact that protein synthesis rates depend on the concentrations of the transcription factors that regulate the corresponding genes. Because of the growing cell volume, such rates are effectively time-dependent. We deal with the effects of volume growth computationally using a rather simple method: the growth of the cell volume is incorporated in our simulations by stochastically adding small volume elements to the cell volume. As an application of this method we study a gene circuit with positive autoregulation that exhibits bistability. We show how the region of bistability becomes diminished by increasing the effect of noise via a reduced copy number of the regulatory protein. Cell volume determines the region of bistability for different noise strengths. The method is general and can also be applied to other cases where synthesis rates of proteins are regulated and an appropriate analytical description is difficult to achieve.


Assuntos
Regulação da Expressão Gênica/fisiologia , Modelos Genéticos , Animais , Divisão Celular/genética , Tamanho Celular , Biologia Computacional/métodos , Replicação do DNA/genética , Redes Reguladoras de Genes , Homeostase/genética , Biossíntese de Proteínas/genética , Processos Estocásticos
14.
PLoS One ; 8(2): e55366, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23418440

RESUMO

The dwell times between two successive steps of the two-headed molecular motor myosin V are governed by non-exponential distributions. These distributions have been determined experimentally for various control parameters such as nucleotide concentrations and external load force. First, we use a simplified network representation to determine the dwell time distributions of myosin V, with the associated dynamics described by a Markov process on networks with absorbing boundaries. Our approach provides a direct relation between the motor's chemical kinetics and its stepping properties. In the absence of an external load, the theoretical distributions quantitatively agree with experimental findings for various nucleotide concentrations. Second, using a more complex branched network, which includes ADP release from the leading head, we are able to elucidate the motor's gating effect. This effect is caused by an asymmetry in the chemical properties of the leading and the trailing head of the motor molecule. In the case of an external load acting on the motor, the corresponding dwell time distributions reveal details about the motor's backsteps.


Assuntos
Modelos Moleculares , Miosina Tipo V/metabolismo , Simulação por Computador , Cinética , Cadeias de Markov
15.
Biophys J ; 100(7): 1747-55, 2011 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-21463588

RESUMO

The molecular motor myosin V has been studied extensively both in bulk and single molecule experiments. Based on the chemical states of the motor, we construct a systematic network theory that includes experimental observations about the stepping behavior of myosin V. We utilize constraints arising from nonequilibrium thermodynamics to determine motor parameters and demonstrate that the motor behavior is governed by three chemomechanical motor cycles. The competition between these cycles can be understood via the influence of external load forces onto the chemical transition rates for the binding of adenosine triphosphate and adenosine diphosphate. In addition, we also investigate the functional dependence of the mechanical stepping rates on these forces. For substall forces, the dominant pathway of the motor network is profoundly different from the one for superstall forces, which leads to a stepping behavior that is in agreement with the experimental observations. Our theory provides a unified description of the experimental data as obtained for myosin V in single motor experiments.


Assuntos
Mecanotransdução Celular , Miosina Tipo V/metabolismo , Citoesqueleto de Actina/efeitos dos fármacos , Citoesqueleto de Actina/metabolismo , Difosfato de Adenosina/farmacologia , Trifosfato de Adenosina/farmacologia , Sítios de Ligação , Fenômenos Biomecânicos/efeitos dos fármacos , Cinética , Mecanotransdução Celular/efeitos dos fármacos , Termodinâmica
16.
Phys Rev E Stat Nonlin Soft Matter Phys ; 75(3 Pt 1): 031121, 2007 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-17500682

RESUMO

We study numerically the dynamics of excitons on discrete rings in the presence of static disorder. Based on continuous-time quantum walks we compute the time evolution of the Wigner function (WF) both for pure diagonal (site) disorder, as well as for diagonal and off-diagonal (site and transfer) disorder. In both cases, large disorder leads to localization and destroys the characteristic phase space patterns of the WF found in the absence of disorder.

17.
J Chem Phys ; 124(12): 124905, 2006 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-16599723

RESUMO

We model coherent exciton transport in dendrimers by continuous-time quantum walks. For dendrimers up to the second generation the coherent transport shows perfect recurrences when the initial excitation starts at the central node. For larger dendrimers, the recurrence ceases to be perfect, a fact which resembles results for discrete quantum carpets. Moreover, depending on the initial excitation site, we find that the coherent transport to certain nodes of the dendrimer has a very low probability. When the initial excitation starts from the central node, the problem can be mapped onto a line which simplifies the computational effort. Furthermore, the long time average of the quantum mechanical transition probabilities between pairs of nodes shows characteristic patterns and allows us to classify the nodes into clusters with identical limiting probabilities. For the (space) average of the quantum mechanical probability to be still or to be again at the initial site, we obtain, based on the Cauchy-Schwarz inequality, a simple lower bound which depends only on the eigenvalue spectrum of the Hamiltonian.

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