Osteosynthesis-associated infection of the lower limbs by multidrug-resistant and extensively drug-resistant Gram-negative bacteria: a multicentre cohort study.

Purpose: The purpose of this study was the clinical and therapeutic assessment of lower-limb osteosynthesis-associated infection (OAI) by multidrug-resistant (MDR) and extensively drug-resistant (XDR) Gram-negative bacteria (GNB), which have been poorly studied to date. Methods: A prospective multicentre observational study was conducted on behalf of ESGIAI (the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) Study Group on Implant-Associated Infections). Factors associated with remission of the infection were evaluated by multivariate and Cox regression analysis for a 24-month follow-up period. Results: Patients ( n = 57 ) had a history of trauma (87.7 %), tumour resection (7 %) and other bone lesions (5.3 %). Pathogens included Escherichia coli ( n = 16 ), Pseudomonas aeruginosa ( n = 14 ; XDR 50 %), Klebsiella spp. ( n = 7 ), Enterobacter spp. ( n = 9 ), Acinetobacter spp. ( n = 5 ), Proteus mirabilis ( n = 3 ), Serratia marcescens ( n = 2 ) and Stenotrophomonas maltophilia ( n = 1 ). The prevalence of ESBL (extended-spectrum ß -lactamase), fluoroquinolone and carbapenem resistance were 71.9 %, 59.6 % and 17.5 % respectively. Most patients ( n = 37 ; 64.9 %) were treated with a combination including carbapenems ( n = 32 ) and colistin ( n = 11 ) for a mean of 63.3 d. Implant retention with debridement occurred in early OAI (66.7 %), whereas the infected device was removed in late OAI (70.4 %) ( p = 0.008 ). OAI remission was achieved in 29 cases (50.9 %). The type of surgery, antimicrobial resistance and duration of treatment did not significantly influence the outcome. Independent predictors of the failure to eradicate OAI were age > 60  years (hazard ratio, HR, of 3.875; 95 % confidence interval, CI95 %, of 1.540-9.752; p = 0.004 ) and multiple surgeries for OAI (HR of 2.822; CI95 % of 1.144-6.963; p = 0.024 ). Conclusions: Only half of the MDR/XDR GNB OAI cases treated by antimicrobials and surgery had a successful outcome. Advanced age and multiple surgeries hampered the eradication of OAI. Optimal therapeutic options remain a challenge.

Impact of Remdesivir on the Treatment of COVID-19 During the First Wave in Spain.

INTRODUCTION: Spain was one of the most affected countries during the first wave of COVID-19, having the highest mortality rate in Europe. The aim of this retrospective study is to estimate the impact that remdesivir-the first drug for COVID-19 approved in the EU-would have had in the first wave. METHODS: This study simulated the impact that remdesivir could have had on the Spanish National Health System (SNHS) capacity (bed occupancy) and the number of deaths that could have been prevented, based on two scenarios: a real-life scenario (without remdesivir) and an alternative scenario (with remdesivir). It considered the clinical results of the ACTT-1 trial in hospitalized patients with COVID-19 and pneumonia who required supplemental oxygen. The occupancy rates in general wards and ICUs were estimated in both scenarios. RESULTS: Remdesivir use could have prevented the admission of 2587 patients (43.75%) in the ICUs. It could have also increased the SNHS capacity in 5656 general wards beds and 1700 ICU beds, showing an increase in the number of beds available of 17.53% (95% CI 3.98%-24.42%) and 23.98% (95% CI 21.33%-28.22%), respectively, at the peak of the occupancy rates. Furthermore, remdesivir use could have prevented 7639 deaths due to COVID-19, which implies a 27.51% reduction (95% CI 14.25%-34.07%). CONCLUSIONS: Remdesivir could have relieved the pressure on the SNHS and could have reduced the death toll, providing a better strategy for the management of COVID-19 during the first wave.

Factors associated with the development of septic shock in patients with candidemia: a post hoc analysis from two prospective cohorts.

BACKGROUND: Almost one third of the patients with candidemia develop septic shock. The understanding why some patients do and others do not develop septic shock is very limited. The objective of this study was to identify variables associated with septic shock development in a large population of patients with candidemia. METHODS: A post hoc analysis was performed on two prospective, multicenter cohort of patients with candidemia from 12 hospitals in Spain and Italy. All episodes occurring from September 2016 to February 2018 were analyzed to assess variables associated with septic shock development defined according to The Third International Consensus Definition for Sepsis and Septic Shock (Sepsis-3). RESULTS: Of 317 candidemic patients, 99 (31.2%) presented septic shock attributable to candidemia. Multivariate logistic regression analysis identifies the following factors associated with septic shock development: age > 50 years (OR 2.57, 95% CI 1.03-6.41, p = 0.04), abdominal source of the infection (OR 2.18, 95% CI 1.04-4.55, p = 0.04), and admission to a general ward at the time of candidemia onset (OR 0.21, 95% CI, 0.12-0.44, p = 0.001). Septic shock development was independently associated with a greater risk of 30-day mortality (OR 2.14, 95% CI 1.08-4.24, p = 0.02). CONCLUSIONS: Age and abdominal source of the infection are the most important factors significantly associated with the development of septic shock in patients with candidemia. Our findings suggest that host factors and source of the infection may be more important for development of septic shock than intrinsic virulence factors of organisms.

An evidence-based bundle improves the quality of care and outcomes of patients with candidaemia.

BACKGROUND: Candidaemia is a leading cause of bloodstream infections in hospitalized patients all over the world. It remains associated with high mortality. OBJECTIVES: To assess the impact of implementing an evidence-based package of measures (bundle) on the quality of care and outcomes of candidaemia. METHODS: A systematic review of the literature was performed to identify measures related to better outcomes in candidaemia. Eight quality-of-care indicators (QCIs) were identified and a set of written recommendations (early treatment, echinocandins in septic shock, source control, follow-up blood culture, ophthalmoscopy, echocardiography, de-escalation, length of treatment) was prospectively implemented. The study was performed in 11 tertiary hospitals in Spain. A quasi-experimental design before and during bundle implementation (September 2016 to February 2018) was used. For the pre-intervention period, data from the prospective national surveillance were used (May 2010 to April 2011). RESULTS: A total of 385 and 263 episodes were included in the pre-intervention and intervention groups, respectively. Adherence to all QCIs improved in the intervention group. The intervention group had a decrease in early (OR 0.46; 95% CI 0.23-0.89; P = 0.022) and overall (OR 0.61; 95% CI 0.4-0.94; P = 0.023) mortality after controlling for potential confounders. CONCLUSIONS: Implementing a structured, evidence-based intervention bundle significantly improved patient care and early and overall mortality in patients with candidaemia. Institutions should embrace this objective strategy and use the bundle as a means to measure high-quality medical care of patients.

Acute liver failure due to visceral leishmaniasis in Barcelona: a case report.

BACKGROUND: Leishmaniasis is an emerging infectious disease. Due to human migration and tourism, visceral leishmaniasis may become more common in non-endemic areas. In the Mediterranean basin, visceral leishmaniasis typically occurs in rural regions. CASE PRESENTATION: We present an unusual urban case of acute liver failure due to visceral leishmaniasis, following a prolonged fever of unknown origin. After obtaining negative results from the bone marrow aspirate, we performed a liver biopsy that elucidated the diagnosis. The liver involvement in visceral leishmaniasis may appear as chronic granulomatous hepatitis. However diffuse hepatitis process, a necro-inflammatory pattern, without forming granulomas were observed in the liver biopsy specimens in this case. Intracytoplasmic Leishmania amastigotes were observed in the liver biopsy specimens and a polymerase chain reaction confirmed the diagnosis. Only five pathological confirmed cases of acute hepatitis due to visceral leishmaniasis have been described so far, just two in adults and both from Barcelona. A revision of the literature is performed. CONCLUSIONS: Acute hepatitis is an uncommon debut of visceral leishmaniasis in immunocompetent patients. Furthermore there are only few cases in the literature that describe the histopathological changes that we found in this patient. In conclusion, in case of acute hepatitis leading to liver failure, leishmaniasis should be considered a differential diagnosis (even in non-endemic countries and without clear epidemiological exposure) and liver biopsy can elucidate the diagnosis.

Multidrug-resistant and extensively drug-resistant Gram-negative prosthetic joint infections: Role of surgery and impact of colistin administration.

Factors influencing treatment outcome of patients with Gram-negative bacterial (GNB) multidrug-resistant (MDR) and extensively drug-resistant (XDR) prosthetic joint infection (PJIs) were analysed. Data were collected (2000-2015) by 18 centres. Treatment success was analysed by surgery type for PJI, resistance (MDR/XDR) and antimicrobials (colistin/non-colistin) using logistic regression and survival analyses. A total of 131 patients (mean age 73.0 years, 35.9% male, 58.8% with co-morbidities) with MDR (n = 108) or XDR (n = 23) GNB PJI were assessed. The most common pathogens were Escherichia coli (33.6%), Pseudomonas aeruginosa (25.2%), Klebsiella pneumoniae (21.4%) and Enterobacter cloacae (17.6%). Pseudomonas aeruginosa predominated in XDR cases. Isolates were carbapenem-resistant (n = 12), fluoroquinolone-resistant (n = 63) and ESBL-producers (n = 94). Treatment outcome was worse in XDR versus MDR cases (P = 0.018). Success rates did not differ for colistin versus non-colistin in XDR cases (P = 0.657), but colistin was less successful in MDR cases (P = 0.018). Debridement, antibiotics and implant retention (DAIR) (n = 67) was associated with higher failure rates versus non-DAIR (n = 64) (OR = 3.57, 95% CI 1.68-7.58; P < 0.001). Superiority of non-DAIR was confirmed by Kaplan-Meir analysis (HR = 0.36, 95% CI 0.20-0.67) and remained unchangeable by time of infection (early/late), antimicrobial resistance (MDR/XDR) and antimicrobials (colistin/non-colistin) (Breslow-Day, P = 0.737). DAIR is associated with higher failure rates even in early MDR/XDR GNB PJIs versus implant removal. Colistin should be preserved for XDR cases as it is detrimental in MDR infections.

Seasonal variability in clinical care of COPD outpatients: results from the Andalusian COPD audit.

OBJECTIVES: Clinical practice in chronic obstructive pulmonary disease (COPD) can be influenced by weather variability throughout the year. To explore the hypothesis of seasonal variability in clinical practice, the present study analyzes the results of the 2013-2014 Andalusian COPD audit with regard to changes in clinical practice according to the different seasons. METHODS: The Andalusian COPD audit was a pilot clinical project conducted from October 2013 to September 2014 in outpatient respiratory clinics of hospitals in Andalusia, Spain (8 provinces with more than 8 million inhabitants) with retrospective data gathering. For the present analysis, astronomical seasons in the Northern Hemisphere were used as reference. Bivariate associations between the different COPD guidelines and the clinical practice changes over the seasons were explored by using binomial multivariate logistic regression analysis with age, sex, Charlson comorbidity index, type of hospital, and COPD severity by forced expiratory volume in 1 second as covariates, and were expressed as odds ratio (OR) with 95% confidence intervals (CIs). RESULTS: The Andalusian COPD audit included 621 clinical records from 9 hospitals. After adjusting for covariates, only inhaler device satisfaction evaluation was found to significantly differ according to the seasons with an increase in winter (OR, 3.460; 95% CI, 1.469-8.151), spring (OR, 4.215; 95% CI, 1.814-9.793), and summer (OR, 3.371; 95% CI, 1.391-8.169) compared to that in autumn. The rest of the observed differences were not significant after adjusting for covariates. However, compliance with evaluating inhaler satisfaction was low. CONCLUSION: The various aspects of clinical practice for COPD care were found to be quite homogeneous throughout the year for the variables evaluated. Inhaler satisfaction evaluation, however, presented some significant variation during the year. Inhaler device satisfaction should be evaluated during all clinical visits throughout the year for improved COPD management.

One-stage revision arthroplasty using cementless stem for infected hip arthroplasties.

The objective of this retrospective study was to evaluate our results with one-stage revision using cementless femoral stem for infected hip arthroplasties. Twenty-four patients were included in the study. The acetabular component was cemented in 9 cases. In 2 patients a structured bone allograft was necessary to fill an acetabular defect. After a mean follow-up of 44.6 months, 23 patients showed no signs of infection (95.8%), the mean functional response according to the Merle d'Aubigné scale was 13.8 and the mean Harris Hip Score was 65.4. One-stage revision hip arthroplasty using cementless femoral stem was associated with a high success rate.

One-stage revision arthroplasty for infected hip replacements.

Infection remains a serious complication after total hip arthroplasty (THA) and is a leading cause of hip revision surgery. It is currently accepted that removal of the prosthesis is essential to curing an infection when facing chronic PJIs with prosthesis loosening. In order to avoid the disadvantages of a two-stage approach, some authors have proposed a one-stage hip revision for the treatment of hip prosthesis infection in selected patients using not only antibiotic-loaded cemented components but also cementless implant. In the case of a one-stage procedure, the patient is exposed to a single major procedure and therefore lower cumulative perioperative risk. A functional prosthesis replacement is completed without exposure to the complications associated with spacers. In addition, there are also benefits both financially and in terms of resource allocation.

Usefulness of histology for predicting infection at the time of hip revision for the treatment of Vancouver B2 periprosthetic fractures.

When facing a Vancouver B2 periprosthetic fracture, the most recommended treatment is the prosthesis replacement. Current tests do not provide enough reliability to identify whether the fracture has been produced on a septic or an aseptic loosened prosthesis. Our aim was to evaluate the usefulness of the histology for the diagnosis of infection in these cases. A total of 11 hip revision procedures were performed (mean age: 78.1 years, 8 women and 3 men). Sensitivity, specificity, positive predictive value and negative predictive value of the histology were 100%, 55.5%, 33.3% and 100% respectively. Of the six patients presenting with a positive histology, four of them had negative cultures (66.6% of false positives). Our results suggest that periprosthetic fractures are a cause of false-positive histology results for the diagnosis of infection during revision of a hip prosthesis for the treatment of Vancouver B2 periprosthetic fractures.

Is linezolid a risk factor for Gram-negative bacillus infections in intensive care unit patients? A comparative study with vancomycin.

BACKGROUND: Linezolid is frequently used in critically ill patients with ventilator-associated pneumonia. Its potent activity against Gram-positive microorganisms and its high tissue penetration may favour Gram-negative colonization and infection. The aim of our study was to evaluate the risk for Gram-negative infections in critically ill patients treated with linezolid or vancomycin. METHODS: The cases of all patients admitted over an 18-month period to a hepatic intensive care unit for ≥ 1 week, and treated with linezolid or vancomycin, were retrospectively reviewed. The main clinical characteristics and infections due to Gram-negative bacteria in the month after starting linezolid or vancomycin were obtained. RESULTS: Seventy-one patients treated with linezolid and 68 treated with vancomycin fulfilled the inclusion criteria. Co-morbidities were similar in both groups. Patients on linezolid treatment had a longer stay in the ICU (mean ± standard deviation 41 ± 38 days vs 18.4 ± 13 days), received this treatment later (14.3 ± 15.1 days vs 6.3 ± 6.5 days), had a higher mean serum creatinine concentration (1.71 ± 1.18 mg/dl vs 1.04 ± 1.04 mg/dl), more often required haemodiafiltration (29.6% vs 13.2%), and 30 day-mortality was higher (42.3% vs 20.6%) than in patients receiving vancomycin. More than 95% in both groups received a broad-spectrum beta-lactam in addition to linezolid or vancomycin. The rate of Gram-negative infection during the following month was 28.2% in the linezolid group and 26.5% in the vancomycin group (p > 0.5). CONCLUSIONS: Linezolid was more frequently used in critically ill patients with longer ICU stay and renal failure. The rate of infection due to Gram-negative microorganisms was similar in patients who received linezolid or vancomycin.

Actualización sobre infecciones intraabdominales y posquirúrgicas / Update on intra-abdominal and post-surgical infections

The present article is an update of the literature onintra-abdominal infection, which represents a spectrumof diseases with a common pathogenesis. Establishinga prompt diagnosis and avoiding treatment delays arekey to achieving the best outcomes. Mortality dependson initiating early appropriate treatment to restore fluidand electrolyte imbalances, supporting the functionof vital organs, providing appropriate broad-spectrumantimicrobial therapy, and achieving adequate sourcecontrol.A multidisciplinary group of Spanish physicians with aninterest in these infections selected the most importantpapers produced in the field during 2005 and 2006.One of the members of the group discussed the contentof each of the selected papers, with a critical reviewby other members of the panel.After a review of the state of the art, papers from the fieldsof epidemiology, pathophysiology, basic science, causativemicroorganisms and microbiological diagnosis, mainclinical syndromes, principles of therapy, new antibioticsand surgical procedures, preventive measures,recommended antimicrobial regimens and guidelineswere discussed by the group. Faculty from this panel havemade an interesting contribution to our understandingand management of intra-abdominal infections at present.Their contribution is particularly relevant for clinicalpractice(AU)

El presente artículo es una puesta al día de la literaturasobre infecciones intraabdominales, que constituyen unagama de procesos con una patogenia común. Para lograrlos mejores resultados tiene una importancia decisivaestablecer un diagnóstico precoz y evitar los retrasos en eltratamiento. La reducción de la mortalidad se basaen iniciar precozmente un tratamiento apropiado pararestaurar los desequilibrios hidroelectrolíticos, en apoyarla función de los órganos vitales, en proporcionar untratamiento adecuado con antibióticos de amplio espectroy en controlar correctamente las fuentes de la infección.Un grupo multidisciplinario de médicos españolesinteresados en este campo seleccionó los trabajos másdestacados que se han publicado sobre el tema en 2005y 2006. Cada artículo seleccionado fue analizado por unmiembro del panel, y el resto de miembros efectuóuna revisión crítica.Después de revisar el estado del arte, el grupo discutiólos trabajos sobre epidemiología, fisiopatología,ciencias básicas, microorganismos causalesy diagnóstico bacteriológico, principales síndromesclínicos, fundamentos del tratamiento, nuevos antibióticosy procedimientos quirúrgicos, medidas preventivas,y pautas y normas antimicrobianas recomendadas.Los miembros de este panel han aportado unainteresante contribución a nuestros conocimientosy a la conducta a seguir actualmente antelas infecciones intraabdominales. Su contribuciónes especialmente relevante para la práctica clínica(AU

Update on intra-abdominal and post-surgical infections

El presente artículo es una puesta al día de la literatura sobre infecciones intraabdominales, que constituyen una gama de procesos con una patogenia común. Para lograr los mejores resultados tiene una importancia decisiva establecer un diagnóstico precoz y evitar los retrasos en el tratamiento. La reducción de la mortalidad se basa en iniciar precozmente un tratamiento apropiado para restaurar los desequilibrios hidroelectrolíticos, en apoyar la función de los órganos vitales, en proporcionar un tratamiento adecuado con antibióticos de amplio espectro y en controlar correctamente las fuentes de la infección.Un grupo multidisciplinario de médicos españolesinteresados en este campo seleccionó los trabajos másdestacados que se han publicado sobre el tema en 2005y 2006. Cada artículo seleccionado fue analizado por unmiembro del panel, y el resto de miembros efectuóuna revisión crítica.Después de revisar el estado del arte, el grupo discutiólos trabajos sobre epidemiología, fisiopatología,ciencias básicas, microorganismos causalesy diagnóstico bacteriológico, principales síndromesclínicos, fundamentos del tratamiento, nuevos antibióticos y procedimientos quirúrgicos, medidas preventivas, y pautas y normas antimicrobianas recomendadas. Los miembros de este panel han aportado unainteresante contribución a nuestros conocimientosy a la conducta a seguir actualmente antelas infecciones intraabdominales. Su contribuciónes especialmente relevante para la práctica clínica

The present article is an update of the literature onintra-abdominal infection, which represents a spectrumof diseases with a common pathogenesis. Establishinga prompt diagnosis and avoiding treatment delays arekey to achieving the best outcomes. Mortality dependson initiating early appropriate treatment to restore fluid and electrolyte imbalances, supporting the functionof vital organs, providing appropriate broad-spectrumantimicrobial therapy, and achieving adequate sourcecontrol.A multidisciplinary group of Spanish physicians with aninterest in these infections selected the most importantpapers produced in the field during 2005 and 2006.One of the members of the group discussed the contentof each of the selected papers, with a critical reviewby other members of the panel.After a review of the state of the art, papers from the fields of epidemiology, pathophysiology, basic science, causative microorganisms and microbiological diagnosis, main clinical syndromes, principles of therapy, new antibiotics and surgical procedures, preventive measures,recommended antimicrobial regimens and guidelineswere discussed by the group. Faculty from this panel havemade an interesting contribution to our understandingand management of intra-abdominal infections at present. Their contribution is particularly relevant for clinical practice (AU)

Using Grote-Hynes theory to quantify dynamical effects on the reaction rate of enzymatic processes. The case of methyltransferases.

Dynamical effects have recently received much attention in the context of the theoretical investigation of enzymatic catalysis. In this paper we use a combination of Grote-Hynes theory with quantum mechanical/molecular mechanical modeling that is a powerful tool to understand and quantify these dynamical effects in a particular enzyme, the glycine N-methyltransferase (GNMT). Comparison of the results obtained for this enzyme with another methyltransferase (catechol O-methyltransferase, COMT) allows us to understand the different nature of the coupling of the environment to the reaction coordinate as a function of the electrostatic interaction established by the reactive subsystem. The transmission coefficients obtained using Grote-Hynes theory are in excellent agreement with molecular dynamics estimations and show that the coupling is higher in GNMT than in COMT. The larger friction observed in GNMT is explained on the basis of the interaction established by the substrate in the active site. The larger value of the friction leads to a smaller value of the reaction frequency and thus also to a larger disagreement with the estimation of the transmission coefficient based on the frozen environment approach.

A computational study of the protein-ligand interactions in CDK2 inhibitors: using quantum mechanics/molecular mechanics interaction energy as a predictor of the biological activity.

We report a combined quantum mechanics/molecular mechanics (QM/MM) study to determine the protein-ligand interaction energy between CDK2 (cyclin-dependent kinase 2) and five inhibitors with the N(2)-substituted 6-cyclohexyl-methoxy-purine scaffold. The computational results in this work show that the QM/MM interaction energy is strongly correlated to the biological activity and can be used as a predictor, at least within a family of substrates. A detailed analysis of the protein-ligand structures obtained from molecular dynamics simulations shows specific interactions within the active site that, in some cases, have not been reported before to our knowledge. The computed interaction energy gauges the strength of protein-ligand interactions. Finally, energy decomposition and multiple regression analyses were performed to check the contribution of the electrostatic and van der Waals energies to the total interaction energy and to show the capabilities of the computational model to identify new potent inhibitors.

Reversible inhibition of mitochondrial protein synthesis during linezolid-related hyperlactatemia.

The objective of the present study was to determine the mitochondrial toxicity mechanisms of linezolid-related hyperlactatemia. Five patients on a long-term schedule of linezolid treatment were studied during the acute phase of hyperlactatemia and after clinical recovery and lactate normalization following linezolid withdrawal. Mitochondrial studies were performed with peripheral blood mononuclear cells and consisted of measurement of mitochondrial mass, mitochondrial protein synthesis homeostasis (cytochrome c oxidase [COX] activity, COX-II subunit expression, COX-II mRNA abundance, and mitochondrial DNA [mtDNA] content), and overall mitochondrial function (mitochondrial membrane potential and intact-cell oxidative capacity). During linezolid-induced hyperlactatemia, we found extremely reduced protein expression (16% of the remaining content compared to control values [100%], P < 0.001) for the mitochondrially coded, transcribed, and translated COX-II subunit. Accordingly, COX activity was also found to be decreased (51% of the remaining activity, P < 0.05). These reductions were observed despite the numbers of COX-II mitochondrial RNA transcripts being abnormally increased (297%, P = 0.10 [not significant]) and the mitochondrial DNA content remaining stable. These abnormalities persisted even after the correction for mitochondrial mass, which was mildly decreased during the hyperlactatemic phase. Most of the mitochondrial abnormalities returned to control ranges after linezolid withdrawal, lactate normalization, and clinical recovery. Linezolid inhibits mitochondrial protein synthesis, leading to decreased mitochondrial enzymatic activity, which causes linezolid-related hyperlactatemia, which resolves upon discontinuation of linezolid treatment.

Catalysis in glycine N-methyltransferase: testing the electrostatic stabilization and compression hypothesis.

Glycine N-methyltransferase (GNMT) is an S-adenosyl-l-methionine dependent enzyme that catalyzes glycine transformation to sarcosine. Here, we present a hybrid quantum mechanics/molecular mechanics (QM/MM) computational study of the reaction compared to the counterpart process in water. The process takes place through an SN2 mechanism in both media with a transition state in which the transferring methyl group is placed in between the donor (SAM) and the acceptor (the amine group of glycine). Comparative analysis of structural, electrostatic, and electronic characteristics of the in-solution and enzymatic transition states allows us to get a deeper insight into the origins of the enzyme's catalytic power. We found that the enzyme is able to stabilize the substrate in its more active basic form by means of a positively charged residue (Arg175) placed in the active site. However, the maximum stabilization is attained for the transition state. In this case, the enzyme is able to form stronger hydrogen bonds with the positively charged amine group. Finally, we show that in agreement with previous computational studies on other methyltransferases, there is no computational evidence for the compression hypothesis, as was formulated by Schowen (Hegazi, M. F., Borchardt, R. T., and Schowen, R. L. (1979) J. Am. Chem. Soc. 101, 4359-4365).

Dynamic and electrostatic effects in enzymatic processes. An analysis of the nucleophilic substitution reaction in haloalkane dehalogenase.

We present an analysis of rare event trajectories for the nucleophilic displacement of a chloride anion of 1,2-dichloroethane by a carboxylate group in haloalkane dehalogenase from Xanthobacterautotrophicus (DhlA) and in aqueous solution. Differences in the transmission coefficient are rationalized on the basis of the electrostatic coupling between the chemical system and the environment. Detailed analysis of the reactive trajectories reveals that the evolution of the hydrogen bond interactions established between the substrate and the environment present significant differences in aqueous solution and in the enzyme. The structure of the enzymatic active site provides a more adequate interaction pattern for the reaction progress.