The outcome of polyethylene glycol fusion augmented by electrical stimulation in a delayed setting of nerve repair following neurotmesis in a rat model

PURPOSE

Polyethylene glycol is known to improve recovery following its use in repair of acute peripheral nerve injury. The duration till which PEG works remains a subject of intense research. We studied the effect of PEG with augmentation of 20Htz of electrical stimulation (ES) following neurorrhaphy at 48 h in a rodent sciatic nerve neurotmesis model.

METHOD

Twenty-four Sprague Dawley rats were divided into 4 groups. In group I, the sciatic nerve was transected and repaired immediately. In group II, PEG fusion was done additionally after acute repair. In group III, repair and PEG fusion were done at 48 h. In group IV, ES of 20Htz at 2 mA for 1 h was added to the steps followed for group III. Weekly assessment of sciatic functional index (SFI), pinprick, and cold allodynia tests were done at 3 weeks and euthanized. Sciatic nerve axonal count and muscle weight were done.

RESULTS

Groups II, III, and IV showed significantly better recovery of SFI (II: 70.10 ± 1.24/III: 84.00 ± 2.59/IV: 74.40 ± 1.71 vs I: 90.00 ± 1.38) (p < 0.001) and axonal counts (II: 4040 ± 270/III: 2121 ± 450/IV:2380 ± 158 vs I: 1024 ± 094) (p < 0.001) at 3 weeks. The experimental groups showed earlier recovery of sensation in comparison to the controls as demonstrated by pinprick and cold allodynia tests and improved muscle weights. Addition of electrical stimulation helped in better score with SFI (III: 84.00 ± 2.59 vs IV: 74.40 ± 1.71) (p < 0.001) and muscle weight (plantar flexors) (III: 0.49 ± 0.02 vs IV: 0.55 ± 0.01) (p < 0.001) in delayed repair and PEG fusions.

CONCLUSION

This study shows that PEG fusion of peripheral nerve repair in augmentation with ES results in better outcomes, and this benefit can be demonstrated up to a window period of 48 h after injury.

The Need of Endodontic Therapy among Patients Attending Tertiary Care Center in Central Nepal

Background Dental caries is considered as the most prevalent oral disease in Nepalese population that frequently needs endodontic therapy or root canal treatment (RCT). Pulp infection is one of the most common sequels of dental caries which when left untreated leads to pulpal necrosis and peri-radicular diseases. Patients usually reports to the dental hospital after there is pain, sensitivity, swelling or fracture of the tooth structure which usually impedes their normal routine of daily life. RCT is one of the efficacious therapeutic procedures that can save the teeth retaining its aesthetics and function. Objective To determine the need of RCT among patients attending Tertiary Care Hospital. Method A cross-sectional epidemiological study was conducted in the Department of Conservative Dentistry and Endodontics over the period of one year from April 2019 to April 2020. Ethical approval was taken from the Institutional Review Committee Kathmandu University School of Medical Sciences. In total, 7566 records of the patients that needed endodontic therapy and other treatments were collected and the need of endodontic therapy versus other treatments were assessed. The data obtained were analyzed using the SPSS version 20. The association between various patient-related variables were calculated by chi square test and mean, standard deviation, frequency and percentage were calculated using descriptive statistics. P value was set at < 0.05 for statistical significance. Result Among the total study population, (n=7566), the mean age was 34.97±14.34 years among which 4387 (58%) were females and 3179 (42%) were males. The type of treatment required by the study participants were significantly associated with age and sex (p < 0.001) and p < 0.001, respectively). Conclusion The findings of this study concluded that there was an increased need for endodontic therapy among patients visiting the department compared to other treatments. There was a significant association between gender and age showing females and elderly patients in greater need for endodontic therapy.

Radiographic Assessment of Occurrence of Pulp Stones in Molars of Selected Adult Nepalese Populations at Tertiary Care Center

Background Pulp stones or "denticles" are a frequent finding in coronal and radicular pulp of primary and permanent dentition. These discrete calcified bodies can be seen in a healthy, diseased and sometimes even in an unerupted tooth. These calcifications are mostly present in molars as free, attached or embedded to dentine of pulp chamber or root canals. Objective To determine the occurrence of pulp stones in molars of selected adult Nepalese population using radiographs and assess the association of its occurrence gender and arch wise. Method A descriptive cross-sectional study was performed using orthopantomogram of total 380 patients (190 male and 190 females) of age group ranging from 16-30 years by convenience sampling. Data were collected through the examination of both hard and soft copies of radiographs under magnification. Pulp stones were scored as present or absent and their association with gender and dental arch were recorded. Descriptive statistics and chi square test was performed to see the prevalence and to compare the occurrence of pulp stone respectively. Result Out of 380 radiographic samples, pulp stones were present in 41.05% of the samples. The occurrence of pulp stones were found to be higher in females than in males, although the difference was not statistically significant (p=0.060).The total number of teeth with pulp stones was 238 and 61 in maxillary and mandibular arches respectively, with statistically significant difference (p<0.001). Conclusion The overall occurrence of pulp stone was found to be 41.05%. It was observed more in females (45.78%) than in males (37%) and more frequently located in maxillary molars (29.2%) than in mandibular molars (8.2%).

Self-confidence Level among Intern Dentists in Performing Endodontic Treatment Procedures in Nepal

Background Endodontics is considered as one of the most difficult and stressful disciplines in dentistry. This might be due to the complex anatomical variations, recent advances in equipment, technology, materials and lack of self-confidence. Objective To determine the self-confidence level among the intern dentists in performing endodontic procedures from six different colleges of Kathmandu University, Nepal. Method A descriptive cross-sectional study was conducted among 145 intern dentists. The online questionnaire regarding confidence level (5 point Likert scale) in different endodontic procedures and difficulty level (easy, ok and difficult) with respect to teeth was distributed. For descriptive purpose, frequency and percentage for each response were calculated. Result Dental interns were confident in performing majority of the normal endodontic procedures, however, they showed less confidence in performing difficult steps like rubber dam application for anterior (74, 51%) and posterior tooth (91, 62.7%), use of electronic apex locator (89, 61.4%), using rotary files (114, 78.6%), management of flare-ups (86, 59.4%), assessment of quality of post-endodontic treatment (85, 58.5%), recall periods (75, 51.6%) and performing post and core (82, 56.6%). Likewise, upper first molars (84, 57.9%) and second molars (104, 71.7%) were found to be the most difficult teeth to treat. Conclusion It can be concluded that majority of the dental interns were confident in performing basic endodontic procedures, however, they were found to have low confidence in performing difficult steps. Further training and exposure should be incorporated to increase their confidence level.

Decontaminating N95 and SN95 masks with ultraviolet germicidal irradiation does not impair mask efficacy and safety

Inadequate supply of filtering facepiece respirators (FFRs) for healthcare workers during a pandemic such as the novel coronavirus outbreak (SARS-CoV-2) is a serious public health issue. The aim of this study was to synthesize existing data on the effectiveness of ultraviolet germicidal irradiation (UVGI) for N95 FFR decontamination. A systematic review (PROSPERO CRD42020176156) was conducted on UVGI in N95 FFRs using Embase, Medline, Global Health, Google Scholar, WHO feed, and MedRxiv. Two reviewers independently determined eligibility and extracted predefined variables. Original research reporting on function, decontamination, or mask fit following UVGI were included. Thirteen studies were identified, comprising 54 UVGI intervention arms and 58 N95 models. FFRs consistently maintained certification standards following UVGI. Aerosol penetration averaged 1.19% (0.70-2.48%) and 1.14% (0.57-2.63%) for control and UVGI arms, respectively. Airflow resistance for the control arms averaged 9.79 mm H₂O (7.97-11.70 mm H₂O) vs 9.85 mm H₂O (8.33-11.44 mm H₂O) for UVGI arms. UVGI protocols employing a cumulative dose >20,000 J/m² resulted in a 2-log reduction in viral load. A >3-log reduction was observed in seven UVGI arms using >40,000 J/m². Impact of UVGI on fit was evaluated in two studies (16,200; 32,400 J/m²) and no evidence of compromise was found. Our findings suggest that further work in this area (or translation to a clinical setting) should use a cumulative UV-C dose of 40,000 J/m² or greater, and confirm appropriate mask fit following decontamination.

Decontaminating N95 and SN95 masks with ultraviolet germicidal irradiation does not impair mask efficacy and safety

Inadequate supply of filtering facepiece respirators (FFRs) for healthcare workers during a pandemic such as the novel coronavirus outbreak (SARS-CoV-2) is a serious public health issue. The aim of this study was to synthesize existing data on the effectiveness of ultraviolet germicidal irradiation (UVGI) for N95 FFR decontamination. A systematic review (PROSPERO CRD42020176156) was conducted on UVGI in N95 FFRs using Embase, Medline, Global Health, Google Scholar, WHO feed, and MedRxiv. Two reviewers independently determined eligibility and extracted predefined variables. Original research reporting on function, decontamination, or mask fit following UVGI were included. Thirteen studies were identified, comprising 54 UVGI intervention arms and 58 N95 models. FFRs consistently maintained certification standards following UVGI. Aerosol penetration averaged 1.19% (0.70-2.48%) and 1.14% (0.57-2.63%) for control and UVGI arms, respectively. Airflow resistance for the control arms averaged 9.79 mm H₂O (7.97-11.70 mm H₂O) vs 9.85 mm H₂O (8.33-11.44 mm H₂O) for UVGI arms. UVGI protocols employing a cumulative dose >20,000 J/m² resulted in a 2-log reduction in viral load. A >3-log reduction was observed in seven UVGI arms using >40,000 J/m². Impact of UVGI on fit was evaluated in two studies (16,200; 32,400 J/m²) and no evidence of compromise was found. Our findings suggest that further work in this area (or translation to a clinical setting) should use a cumulative UV-C dose of 40,000 J/m² or greater, and confirm appropriate mask fit following decontamination.

AB0395 SYSTEMIC LUPUS ASSOCIATED MACROPHAGE ACTIVATION SYNDROME – A SINGLE CENTRE EXPERIENCE FROM INDIA

Background:

Macrophage activation syndrome (MAS) is a potentially fatal complication of systemic lupus erythematosus (SLE).(1) Overlapping clinical features of SLE activity with MA makes it a clinical diagnosis. There is limited data from developing countries like India.

Objectives:

To study the clinical features, treatment, and outcomes in SLE-MAS.

Methods:

This single-centre, retrospective study included patients fulfilling SLICC 2011 criteria for SLE, admitted from January 2017 to November 2019, and diagnosed as MAS by a team of attending physicians. Their demographic and clinical data, treatment, and outcomes were recorded. H score and SLEDAI were calculated. Patients were assessed for HLH classification criteria (2004) and preliminary diagnostic criteria for MAS in childhood SLE (cSLE).

Results:

Sixteen patients (median age – 26 years, 15 females) were included. Twelve patients (75%) had MAS as the initial presentation of SLE. The common clinical features were fever (100%) and cytopenias (100%). The mean duration of symptoms was 60 days. The most frequent biochemical abnormalities were high ferritin (>500 ng/ml, 100%) and elevated transaminases (100%, aspartate transaminase > alanine transaminase). Common complications were renal (43.8%), neurological (43.8%), and coagulopathy (43.8%). Seven and 16 patients fulfilled the HLH 2004 and cSLE – MAS preliminary criteria, respectively. The median H score was 222, giving a cumulative probability of 96%. All the patients received high-dose steroids. Cyclophosphamide pulse and cyclosporine were administered to 8 (50%) and 6 (37.5%) patients respectively. There were four (25%) in-hospital mortalities.

CharacteristicN=16Age (years)26 (19.5 – 30)Duration of symptoms (days)60 (18.7 – 90)Fever16 (100)Pancreatitis1 (6.3)Renal7 (43.8)Neurological7 (43.8)Myocarditis6 (37.5)Hepatomegaly7 (43.8)Splenomegaly3 (18.8)Lymphadenopathy12 (75)Anaemia16 (100)Leukopenia13 (82)Thrombocytopenia14 (88.2)Coagulopathy7 (43.8)Concomitant infection3 (18.8)H score222 (193 – 254)cSLE-MAS diagnostic criteria16 (100%)HLH 2004 (≥5)7 (43.8)Corticosteroids16 (100%)Cyclophosphamide8 (50%)Intravenous immunoglobulin2 (12.5%)Cyclosporine6 (37.5%)Death4 (25%)

All data presented as n (%) and median (IQR)

cSLE-MAS – Childhood systemic lupus erythematosus – Macrophage activation syndrome, HLH – Hemophagocytic lymphohistiocytosis

ParameterN = 16Haemoglobin (g/dL)6.9 (5.7 – 7.8)Total leucocyte count (cells/mm3)1400 (1025 -3175)<10003 (18.8)1000 – 25009 (56.3)2500 - 40001 (6.3)Platelet (cells/mm3)57500 (23500 – 95250)<200003 (18.8)20000 – 500003 (18.8)50000 – 1 lac8 (50)Serum ferritin > 500 ng/ml16 (100%)Fibrinogen2.48 (1.6 – 4)Triglycerides (mg/dL)375 (294 -470)AST/ALT (U/L)153 (113 – 234) / 90 (68 – 170)Procalcitonin (pg/mL)0.8 (0.3 – 1.4)Lactate dehydrogenase (U/L)1674 (1081 – 2184)Erythrocyte sedimentation rate (mm in 1sthour)61 (44 – 69)C- reactive protein (mg/L)36 (6.3 – 52)Bone marrow examination14 (87.5)Increased histiocytes with hemophagocytosis5 (32.5)

All data presented as n (%) and median (IQR)

ALT – Alanine transaminase, AST – Aspartate transaminase

Conclusion:

Fever, cytopenia, high ferritin, and elevation of transaminases were the commonest features in this series of SLE-MAS. SLE-MAS carried a high mortality (25%) despite aggressive treatment.

References:

[1]Gavand P-E, Serio I, Arnaud L, Costedoat-Chalumeau N, Carvelli J, Dossier A, et al. Clinical spectrum and therapeutic management of systemic lupus erythematosus-associated macrophage activation syndrome: A study of 103 episodes in 89 adult patients. Autoimmun Rev. 2017;16(7):743–9.

Acknowledgments:

NONE

Disclosure of Interests:

None declared

A Comparative Evaluation of Removal of Intracanal Calcium Hydroxide with Endoactivator System and Mechanical Instrumentation with K File, Using Two Irrigating Solutions: an in Vitro Study

Background Calcium Hydroxide [Ca(OH)2] is widely used intracanal medicament in endodontics due to its antimicrobial activity against persistent microorganisms. Although routine use of calcium hydroxide is highly recommended, its removal at the time of canal obturation is equally important and challenging because its remnant might prevent the sealer penetration into dentinal tubules, potentially interact with zinc oxide eugenol sealers making them brittle and granular, and adversely affect the bonding of resin sealer adhesion thus significantly increasing the apical leakage of root canal treated teeth. Removal of intracanal calcium hydroxide is performed usually with different irrigants in combinations with ultrasonic, sonic, hand or rotary instruments. Objective The objective of this study is to evaluate the efficacy of Endoactivator system and mechanical instrumentation with K files using two irrigants for removal of intracanal Ca(OH)2. Method Forty extracted single rooted human mandibular premolars were collected and divided into two groups of 20 samples each (N=40; Group A: 1-20; Group B: 21-40). All samples were decoronated, instrumented, irrigated, dried and filled with Ca(OH)2 paste. Samples were stored in a humidor for a week and were instrumented with conventional k-file (Group A) and Endoactivator system (Group B). A radiograph was taken to evaluate the remnants of intracanal medicament. Result Overall there is not any statistically significant difference on any method of intracanal calcium hydroxide removal (p=0.45). However, on section wise comparison of efficacy of Ca(OH)2 removal, Endoactivator seems to be more effective than hand files on apical section (p=0.047). There is no statistically significant difference on coronal and middle segments between two methods (p=0.99). Conclusion The efficacy of removal of calcium hydroxide medicament from overall canal by conventional method and endoactivator system is similar though endoactivator system seems to be relatively more efficient on apical portion of root.

Alternatives to Fight Against Coccidiosis: A Review

Coccidiosis is one of the most important parasitic diseases of poultry with economic losses. The loss is mainly due to the poor feed conversion and increased mortality. Nowadays, farmers rely heavily on prophylactic and therapeutic use of chemical compounds for the management of coccidiosis. The conventional anti-coccidials, however, are associated with residual effects and increased resistance. Similarly, increasing consumer awareness and their pressure for natural food has increased governmental pressure basically. Because of regulatory change, there is increasing pressure to phase out the chemical anticoccidials in diet of farm animals. Moreover, there are renewed management practices as alternatives that are safe, little/no residual effects, and economical. Non-conventional compounds such as Mannan-oligosaccharides (MOS), organic acids, phyto-chemicals, probiotics and essentials oils have shown encouraging result against coccidian growth in intestinal mucosa of chicken and turkey. But, comprehensive studies on chemical structure, modes of action and residual effects is needed to unravel their applicability and effectiveness in the field conditions.

Infections from seven clinical trials of ixekizumab, an anti-interleukin-17A monoclonal antibody, in patients with moderate-to-severe psoriasis

BACKGROUND

Infections are associated with biological therapies in psoriasis.

OBJECTIVES

To summarize the incidence of infections in patients with moderate-to-severe psoriasis treated with ixekizumab, an anti-interleukin-17A monoclonal antibody.

METHODS

Infections are summarized from an integrated database of seven controlled and uncontrolled ixekizumab psoriasis trials. Data are presented from placebo-controlled induction (weeks 0-12; UNCOVER-1, UNCOVER-2 and UNCOVER-3) and maintenance periods (weeks 12-60; UNCOVER-1 and UNCOVER-2), and all patients exposed to ixekizumab pooled from all seven trials. Comparisons with etanercept were made during the induction period of two trials (UNCOVER-2 and UNCOVER-3). Incidence and exposure-adjusted incidence rates (IRs) per 100 patient-years (PYs) are reported.

RESULTS

Overall, 4209 patients were treated with ixekizumab (6480 PY). During induction (weeks 0-12), overall infection rates were higher in patients treated with ixekizumab (27%) vs. placebo (23%, P < 0·05); however, specific infection rates were comparable overall across treatment groups. IRs of infections did not increase with longer-term exposure. For all patients treated with ixekizumab (all seven trials), the incidence of serious infections was low (2%, IR 1·3). Candida infections, including eight cases of oesophageal candidiasis, were adequately managed with antifungal therapy, were noninvasive and did not lead to discontinuation.

CONCLUSIONS

Overall, infections occurred in a higher percentage of patients treated with ixekizumab vs. placebo during the first 12 weeks of treatment; however, specific infection rates were comparable overall across treatment groups. Incidences of serious infections were low and similar across treatment groups.

Endodontic management of radix paramolaris with six canals: a clinical case report

Endodontic therapy of mandibular molars is a challenging task due to its varied root canal morphology. A mandibular first molar with additional buccal root (Radix paramolaris) and additional distolingual root (Radix Entomolaris) is an example of its varied anatomy. A successful management of atypical root canal configurations is an important aspect in determining the success rate of root canal therapy. The detail knowledge of the root morphology and canal anatomy allows the clinician for accurate location of the extra roots and canals and accordingly the refinement of the access cavity for the stress free entry of complex anatomy. Hence, for a successful root canal therapy, clinician must be aware of the external and internal anatomic variations .The aim of this clinical case report is to present and describe the unusual presence of two separate mesial roots and six root canals in mandibular first molar, detected during routine endodontic therapy.

Perioperative management of two cases of hemophilia with spontaneous intracerebral hemorrhage undergoing emergency craniotomy in resource constrained setup of Nepal

Patients with hemophilia are prone to develop spontaneous intracranial hemorrhage. It carries a significant risk of morbidity and mortality. In this case series, we report two cases of hemophilia who suffered spontaneous intracerebral hemorrhage with features of raised intracranial pressure and were successfully managed perioperatively. The patients were managed with early intensive care unit management, measures to reduce intracranial pressure, perioperative clotting factor administration, airway management and surgery to decrease the raised intracranial pressure. Both patients improved following surgery and were discharged home. Perioperative multidisciplinary management of hemophilia is discussed in this series.

Randomized Control Trial of Kangaroo Mother Care in Low Birth Weight Babies at a Tertiary Level Hospital

Introduction: This study was conducted to compare the effect of Kangaroo Mother Care (KMC) and conventional methods of care on weight gain, occurrence of hypothermia and apnea and duration of hospital stay among Low Birth Weight (LBW) babies. Materials and Methods: It was a randomized control trial conducted at a tertiary level hospital for a period of one year from June 2009 to May 2010. Total 126 stable LBW babies weighing less than 2000 gm and fulfilling inclusion criteria were included in the study. Neonates enrolled for the study were allocated to either KMC or control group using random number table. KMC group was subjected to Kangaroo mother care of at least six hours per day in not more than four sittings. In control group, babies were adequately clothed, covered and kept with their mother and if required were kept under radiant warmer. Recording of temperature in KMC group was done before, during and after KMC. In control group temperature was taken every 4 hours. Weighing of baby was done twice daily on electronic weighing scale. Results: Median daily weight gain (IQR) was 10 (6- 20) gm in KMC group as compared to 7 (0-10) gm in control group (p<0.001). Mean weight gain was 12.11±9.04 gm in KMC group as compared to 3.29±15.81 gm in control group (p<0.001). Incidence of hypothermia was more in control group (12.6%) as compared to KMC group (3.1%) (p=0.048). Duration of hospital stay was less in control group as compared to KMC group (p=0.015). Conclusion: LBW babies less than 2000 gm who receive KMC show better weight gain and have less incidence of hypothermia than those who do not receive KMC. DOI: http://dx.doi.org/10.3126/jnps.v34i1.8960   J Nepal Paediatr Soc 2014;34(1):18-23

Fictitious pseudo Meig’s syndrome: A medical emergency

The present case scenario deals with an acute on chronic symptomatology, and collapsed state of the patient with poor vitals on admission in casualty. Clinical work up pointing to an elevated serum CA 125 levels and USG pelvis suggesting peritoneal adhesions with cystic to firm mass in left ovary and minimal free fluid in abdomen and cul de sac, X Ray chest suggesting right sided Pleural effusion. It was after careful evaluation of the case, with past and present history along with signs, symptommatology and intraoperative findings that differentials like Chronic granulomatous lesions, endometriosis, Neoplastic lesions with metastasis and Meig’s syndrome or Pseudo Meig’s were evaluated. Finally, a diagnosis of genital tuberculosis with enodmetriosis was confirmed on histopathological evaluation. DOI: http://dx.doi.org/10.3126/jcmsn.v7i1.5975 JCMSN 2011; 7(1): 57-64

Co-trimoxazole-induced myopia in an HIV-positive patient

Co-trimoxazole is a commonly used drug in the treatment and prophylaxis of opportunistic infections in HIV seropositive patients. We report a case of a 35-year-old HIV-infected man who presented with blurring of vision one week following initiation of co-trimoxazole therapy. A diagnosis of co-trimoxazole-induced myopia, a known idiosyncratic drug reaction, was made. The drug was withheld and the myopia resolved completely. Although in this patient the ocular condition resolved completely, serious ocular adverse reactions have also been reported with co-trimoxazole. This case report highlights the occurrence of ocular adverse drug reactions (ADRs) in HIV-infected patients on co-trimoxazole and the complexity of drug interactions.

Substance use among third year medical students of Nepal

BACKGROUND

Substance use is very rampant in a developing country like Nepal. Unfortunately, medical field is not exempt from it either. Substance use among medical students and doctors not only reduces their efficiency at present but also increases their DALY on long term. The main objectives of the study were to assess the prevalence of substance use among medical student and to find out whether substance use started before or after joining the medical school.

METHODS

The study design employed for the research was descriptive cross sectional. A structured questionnaire about current use of tobacco, alcohol and marijuana was used to collect the data from third year students from eight medical and one dental college from across the country having 2006 batch.

RESULTS

The overall response rate was 74.12% (N=510). Among those who responded, prevalence of substance use was 49.6%, of which 38.2% were Nepalese nationals and 11.4% were foreign nationals and 39% were male and 10.6% female. Alcohol based product users were 52.3%, tobacco based product users were 55% and marijuana users were 65.7% and all started using them after joining the medical school.

CONCLUSIONS

Almost half of the respondents were involved in some sort of substance use and more than half of those using started after joining medical school. Hence if proper measures are taken to address this then its prevalence can be significantly reduced if not eliminated completely.

Structure of Mycobacterium tuberculosis single-stranded DNA-binding protein. Variability in quaternary structure and its implications

Single-stranded DNA-binding protein (SSB) is an essential protein necessary for the functioning of the DNA replication, repair and recombination machineries. Here we report the structure of the DNA-binding domain of Mycobacterium tuberculosis SSB (MtuSSB) in four different crystals distributed in two forms. The structure of one of the forms was solved by a combination of isomorphous replacement and anomalous scattering. This structure was used to determine the structure of the other form by molecular replacement. The polypeptide chain in the structure exhibits the oligonucleotide binding fold. The globular core of the molecule in different subunits in the two forms and those in Escherichia coli SSB (EcoSSB) and human mitochondrial SSB (HMtSSB) have similar structure, although the three loops exhibit considerable structural variation. However, the tetrameric MtuSSB has an as yet unobserved quaternary association. This quaternary structure with a unique dimeric interface lends the oligomeric protein greater stability, which may be of significance to the functioning of the protein under conditions of stress. Also, as a result of the variation in the quaternary structure the path adopted by the DNA to wrap around MtuSSB is expected to be different from that of EcoSSB.

Crystallization and preliminary X-ray studies of the single-stranded DNA-binding protein from Mycobacterium tuberculosis

Single-stranded DNA-binding proteins play an important role in DNA replication, repair and recombination. The protein from Mycobacterium tuberculosis (MtSSB) is a tetramer with 164 amino-acid residues in each subunit. The protein readily crystallizes in space group P3(1)21 (or P3(2)21) at pH 7.4 under appropriate conditions. Under different conditions, but at the same pH, orthorhombic crystals belonging to space group I222 or I2(1)2(1)2(1) were obtained after several months. Similar orthorhombic crystals were obtained when protein samples stored for several months were used for crystallization. The orthorhombic crystals obtained in different experiments, though similar to one another, exhibited variations in unit-cell parameters, presumably on account of different extents of proteolytic cleavage of the C-terminal region. Molecular-replacement calculations using different search models did not yield the structure. As part of attempts to solve the structure using isomorphous replacement, a good mercury derivative of the trigonal crystal has been prepared.

Chimeras between single-stranded DNA-binding proteins from Escherichia coli and Mycobacterium tuberculosis reveal that their C-terminal domains interact with uracil DNA glycosylases

Uracil, a promutagenic base in DNA can arise by spontaneous deamination of cytosine or incorporation of dUMP by DNA polymerase. Uracil is removed from DNA by uracil DNA glycosylase (UDG), the first enzyme in the uracil excision repair pathway. We recently reported that the Escherichia coli single-stranded DNA binding protein (SSB) facilitated uracil excision from certain structured substrates by E. coli UDG (EcoUDG) and suggested the existence of interaction between SSB and UDG. In this study, we have made use of the chimeric proteins obtained by fusion of N- and C-terminal domains of SSBs from E. coli and Mycobacterium tuberculosis to investigate interactions between SSBs and UDGs. The EcoSSB or a chimera containing its C-terminal domain interacts with EcoUDG in a binary (SSB-UDG) or a ternary (DNA-SSB-UDG) complex. However, the chimera containing the N-terminal domain from EcoSSB showed no interactions with EcoUDG. Thus, the C-terminal domain (48 amino acids) of EcoSSB is necessary and sufficient for interaction with EcoUDG. The data also suggest that the C-terminal domain (34 amino acids) of MtuSSB is a predominant determinant for mediating its interaction with MtuUDG. The mechanism of how the interactions between SSB and UDG could be important in uracil excision repair pathway has been discussed.

Distinct properties of Mycobacterium tuberculosis single-stranded DNA binding protein and its functional characterization in Escherichia coli

Single-stranded DNA binding proteins (SSBs) play an essential role in various DNA functions. Characterization of SSB from Mycobacterium tuberculosis, which infects nearly one-third of the world's population and kills about 2-3 million people every year, showed that its oligomeric state and various in vitro DNA binding properties were similar to those of the SSB from Escherichia coli. In this study, use of the yeast two-hybrid assay suggests that the ECO:SSB and the MTU:SSB are even capable of heterooligomerization. However, the MTU:SSB failed to complement a Deltassb strain of E. coli. The sequence comparison suggested that MTU:SSB contained a distinct C-terminal domain. The C-terminal domain of ECO:SSB interacts with various cellular proteins. The chimeric constructs between the N- and C-terminal domains of the MTU:SSB and ECO:SSB exist as homotetramers and demonstrate DNA binding properties similar to the wild-type counterparts. Despite similar biochemical properties, the chimeric SSBs also failed to complement the Deltassb strain of E.coli. These data allude to the occurrence of a 'cross talk' between the N- and the C-terminal domains of the SSBs for their in vivo function. Further, compared with those of the ECO:SSB, the secondary/tertiary interactions within MTU:SSB were found to be less susceptible to disruption by guanidinium hydrochloride. Such structural differences could be exploited for utilizing such essential proteins as crucial molecular targets for controlling the growth of the pathogen.

Rapid synthesis of a 5'-fluorinated oligodeoxy-nucleotide: a model antisense probe for use in imaging with positron emission tomography (PET)

5'-Deoxy-5'-fluoro-O4-methylthymidine was synthesized by the reaction of the corresponding 5'-O-tosylate with KF in the presence of Kryptofix [222] and coupled to a 5'-phosphoramidite-activated CPG-bound oligodeoxynucleotide. The sequence of reactions and purifications were accomplished within 4 h, a necessary condition of the development of radiofluorinated antisense oligodeoxynucleotide probe for use with PET.