Thoracic paravertebral nerve block combined laryngeal mask airway with preservation of spontaneous breathing can accelerate postoperative recovery.

OBJECTIVE: This study aimed to examine the potential benefits of Thoracic Paravertebral Nerve Block (TPVB) coupled with Laryngeal Mask Airway (LMA) and the maintenance of spontaneous breathing anesthesia, in contrast to general anesthesia utilizing double-lumen endobronchial intubation, on promoting recovery following thoracoscopic surgery. PATIENTS AND METHODS: A randomized controlled trial was carried out involving sixty patients set for Video-Assisted Thoracoscopic Surgery (VATS) at the Affiliated People's Hospital of Jiangsu University from February 2021 to January 2022. Patients were randomized to either the TPVB and LMA with spontaneous breathing anesthesia group (non-intubation group, NI group) or the general anesthesia with double-lumen endobronchial intubation group (Intubation group, I group). The primary outcome measured was the duration of hospitalization. Secondary outcomes included early postoperative rehabilitation indicators, postoperative complications, Visual Analogue Score (VAS), and inflammatory response markers. RESULTS: Patients in the NI group experienced significantly shorter hospital stays than those in the I group (p < 0.05). Early postoperative recovery, assessed by metrics including the first exhaust time, food intake time, first ambulation time, and duration of chest-tube placement, was superior in the NI group (p < 0.05). Postoperative complications such as nausea and vomiting, pulmonary infection, atelectasis, sore throat, and hoarseness, along with cortisol and C-reactive protein (CRP) levels at the end of the operation and 24 h post-operation, and VAS values within the first 12 h post-operation, were significantly lower in the NI group (p < 0.05). However, blood loss, operation time, and VAS values at 24 h and 48 h post-surgery showed no significant differences between the two groups. CONCLUSIONS: Our findings suggest that TPVB, in conjunction with LMA and spontaneous breathing anesthesia, may expedite postoperative recovery in patients undergoing VATS.

Current status and trends for natural products on hyperuricemia research: a scientometric visualization analysis from 2000 to 2021.

OBJECTIVE: Hyperuricemia (HUA) is a metabolic disease caused by abnormal purine metabolism in the body. It also shows a trend of high incidence among younger people worldwide. More and more studies have shown that natural products can be used to treat HUA, and the literature in this field has been increasing in recent years. However, few bibliometric analyses have systematically examined this field. Our study aims to analyze the published literature to identify trends and hotspots in natural product therapy for HUA, present the research status and summarize critical topics. MATERIALS AND METHODS: A literature search was conducted through the Web of Science Core Collection (WOSCC) database, using Bibliometric R, VOS Viewer, and CiteSpace to examine the eligible publications. A total of 1,201 publications (1,040 articles and 161 reviews) concerning natural product therapy for HUA research between 2000 and 2021 were ultimately included. RESULTS: In recent years, research articles in this field have increased. China and the United States are the main driving forces in this field and have a high academic reputation. China published the most relevant articles, while the United States cited the most. Chinese Acad Sci is the institution with the most relevant research results. Flavonoids, xanthine oxidase, antioxidant activity, and gout are the current research hotspots and future research trend topics. CONCLUSIONS: Our results provide a general overview of the leading research directions of natural products in HUA research. The mechanisms of natural products, especially those related to xanthine oxidase, antioxidant activity, and gout, may soon become hot spots and should be closely watched. The field of natural product therapy for HUA is going through rapid development, and our research provides a valuable reference for clinical researchers and practitioners.

[Clinical features and outcomes of newly diagnosed follicular lymphoma concurrent with diffuse large B-cell lymphoma component].

Objective: To explore the clinical features and survival of newly diagnosed follicular lymphoma (FL) patients with diffuse large B-cell lymphoma (DLBCL) component. Methods: 1845 newly diagnosed FL patients aged ≥ 18 years with grades 1-3a in 11 medical centers in China from 2000 to 2020 were included, and patients with DLBCL component were screened. The clinical data and survival data of the patients were retrospectively analyzed, and the prognostic factors were screened by univariate and multivariate analysis. Results: 146 patients (7.9% ) with newly diagnosed FL had DLBCL component. The median age was 56 (25-83) years, 79 males (54.1% ) . The pathology of 127 patients showed the proportion of DLBCL component. Patients were divided into two groups according to whether the proportion of DLBCL component was ≥ 50% . The study found that patients with DLBCL component ≥ 50% had higher grade 3 ratio (94.3% vs 91.9% , P=0.010) , Ki-67 index ≥ 70% ratio (58.5% vs 32.9% , P=0.013) and PET-CT SUVmax ≥ 13 ratio (72.4% vs 46.3% , P=0.030) than patients with DLBCL component<50% . All patients received CHOP or CHOP like ± rituximab chemotherapy. The overall response rate (ORR) was 88.2% , and the complete response (CR) rate was 76.4% . In the groups with different proportions of DLBCL component, there was no significant difference in the remission rate after induction treatment and the incidence of disease progression within 2 years after initiation of treatment (POD24) (P<0.05) . The overall estimated 5-year progression free survival (PFS) rate was 58.9% , and the 5-year overall survival (OS) rate was 90.4% . The 5-year OS rate of POD24 patients was lower than that of non POD24 patients (70.3% vs 98.5% , P<0.001) . Compared with non maintenance treatment of rituximab, maintenance treatment of rituximab could not benefit the 5-year PFS rate (57.7% vs 58.8% , P=0.543) , and the 5-year OS rate had a benefit trend, but the difference was not statistically significant (100% vs 87.8% , P=0.082) . Multivariate analysis showed that failure to reach CR after induction treatment was an independent risk factor for PFS (P=0.006) , while LDH higher than normal was an independent risk factor for OS (P=0.031) . Conclusion: FL patients with DLBCL component ≥50% have more invasive clinical and pathological features. CHOP/CHOP like ± rituximab regimen can improve the clinical efficacy of patients. Rituximab maintenance therapy can not benefit the PFS and OS of patients. Failure to reach CR after induction therapy was the independent unfavorable factor for PFS.

Degradable RGD-Functionalized 3D-Printed Scaffold Promotes Osteogenesis.

To establish an ideal microenvironment for regenerating maxillofacial defects, recent research interests have concentrated on developing scaffolds with intricate configurations and manipulating the stiffness of extracellular matrix toward osteogenesis. Herein, we propose to infuse a degradable RGD-functionalized alginate matrix (RAM) with osteoid-like stiffness, as an artificial extracellular matrix, to a rigid 3D-printed hydroxyapatite scaffold for maxillofacial regeneration. The 3D-printed hydroxyapatite scaffold was produced by microextrusion technology and showed good dimensional stability with consistent microporous detail. RAM was crosslinked by calcium sulfate to manipulate the stiffness, and its degradation was accelerated by partial oxidation using sodium periodate. The results revealed that viability of bone marrow stem cells was significantly improved on the RAM and was promoted on the oxidized RAM. In addition, the migration and osteogenic differentiation of bone marrow stem cells were promoted on the RAM with osteoid-like stiffness, specifically on the oxidized RAM. The in vivo evidence revealed that nonoxidized RAM with osteoid-like stiffness upregulated osteogenic genes but prevented ingrowth of newly formed bone, leading to limited regeneration. Oxidized RAM with osteoid-like stiffness facilitated collagen synthesis, angiogenesis, and osteogenesis and induced robust bone formation, thereby significantly promoting maxillofacial regeneration. Overall, this study supported that in the stabilized microenvironment, oxidized RAM with osteoid-like stiffness offered requisite mechanical cues for osteogenesis and an appropriate degradation profile to facilitate bone formation. Combining the 3D-printed hydroxyapatite scaffold and oxidized RAM with osteoid-like stiffness may be an advantageous approach for maxillofacial regeneration.

Age distribution of human papillomavirus infection and neutralizing antibodies in healthy Chinese women aged 18-45 years enrolled in a clinical trial.

OBJECTIVES: Data from clinical trials of human papillomavirus (HPV) vaccines showed that women naïve (negative for both type-specific antibodies and DNA) to vaccine types would derive benefit from vaccination; therefore, an understanding of the proportion of naïve women in different age groups is important for developing HPV vaccination strategies. METHODS: From November 2012 to April 2013, a total of 7372 healthy women aged 18-45 years were recruited in five provinces in China. Cervical specimens and serum samples were collected for each woman at entry. Cervical specimens were first tested by the HPV DNA enzyme immunoassay method; if positive, the specimens were then tested by reverse hybridization line probe assay and HPV-16 and HPV-18 specific polymerase chain reactions. Neutralizing antibodies against HPV-16 or HPV-18 were tested with a pseudovirion-based neutralization assay. RESULTS: The overall prevalence of high-risk HPV DNA was 14.8% (1088/7367, 95% CI 14.0-15.6), and the seroprevalence of neutralizing antibodies against HPV-16 and HPV-18 was 12.6% (925/7367) and 4.9% (364/7367), respectively. In younger women (18-26 years) and middle-aged women (27-45 years), 83.8% (3116/3719) and 81.4% (2968/3648) were naïve to both HPV-16 and HPV-18 (both neutralizing antibodies and DNA were negative), respectively. In addition, 98.5% (3664/3719) and 98.0% (3575/3648) of the younger or middle-aged women were naïve to at least one HPV type (HPV-16 or HPV-18). DISCUSSION: This study revealed that the majority of Chinese women aged 18-26 years and 27-45 years were naïve to both HPV-16 and HPV-18 and would thus derive full benefit from bivalent HPV vaccination.

Engineering Disease-Resistant Cassava.

Manihot esculenta Crantz (cassava) is a food crop originating from South America grown primarily for its starchy storage roots. Today, cassava is grown in the tropics of South America, Africa, and Asia with an estimated 800 million people relying on it as a staple source of calories. In parts of sub-Saharan Africa, cassava is particularly crucial for food security. Cassava root starch also has use in the pharmaceutical, textile, paper, and biofuel industries. Cassava has seen strong demand since 2000 and production has increased consistently year-over-year, but potential yields are hampered by susceptibility to biotic and abiotic stresses. In particular, bacterial and viral diseases can cause severe yield losses. Of note are cassava bacterial blight (CBB), cassava mosaic disease (CMD), and cassava brown streak disease (CBSD), all of which can cause catastrophic losses for growers. In this article, we provide an overview of the major microbial diseases of cassava, discuss current and potential future efforts to engineer new sources of resistance, and conclude with a discussion of the regulatory hurdles that face biotechnology.

[Impact of fine particulate matters on the daily number of emergency visits and outpatient visits of 5 hospitals in Beijing, Shanghai, and Guangzhou, 2013-2015].

Objective: To explore the effect of fine particulate matters (PM(2.5)) exposure on emergency visits and outpatient visits of 5 hospitals in Beijing, Shanghai and Guangzhou from 2013 to 2015. Methods: Using convenient sampling method, 5 general hospitals in Beijing, Shanghai and Guangzhou were selected which included Beijing hospital, China-Japan friendship hospital, Xinhua hospital affiliated to Shanghai jiaotong University School of Medicine, the liwan hospital of the third affiliated hospital and the first affiliated hospital of Guangzhou Medical University. The emergency and outpatient data, air pollution monitoring data and meteorological data were collected from January 1, 2013 to December 31, 2015. A generalized additive model was used to analyze the effect of PM(2.5) exposure on daily hospital emergency and outpatient visits, and Meta analysis was used to obtain the combined effect value. Results: The number of emergency and outpatient visits of 5 hospitals was 1 378 501 and 18 139 779 in total, respectively. The mean±SD of PM(2.5) exposures in Beijing hospital, China-Japan friendship hospital, Xinhua hospital affiliated to Shanghai jiaotong University School of Medicine, the liwan hospital of the third affiliated hospital and the first affiliated hospital of Guangzhou Medical University were (81.8±68.7), (83.2±69.7), (54.4±34.1), (43.5±24.8) µg/m(3), respectively. Results of single pollutant model analysis showed that 0-1 day lag concentrations of PM(2.5) had the largest effect on emergency visits and outpatient visits. For a 10 µg/m(3) increase of PM(2).5 concentration, excess risk (ER) (95%CI) of emergency and outpatient visits was 0.56% (0.14%, 0.99%) and0.63% (0.07%, 1.19%), respectively. After adjusting for O(3), NO(2), SO(2), and CO, for a 10 µg/m(3) increase of PM(2.5) concentrations, the ER (95%CI) of emergency visits was 0.50% (0.10%, 0.90%), 0.34% (-0.02%, 0.69%), 0.36% (0.02%, 0.69%) and 0.56% (0.10%, 1.03%), respectively and the ER (95% CI) of outpatient visits was 0.65% (0.08%, 1.21%), 0.29% (-0.17%, 0.75%), 0.48% (-0.06%, 1.03%) and 0.48%(-0.02%, 0.99%), respectively. Conclusion: Our results suggested that PM(2.5) exposure can increase emergency and outpatient visits of 5 hospitals in Beijing, Shanghai and Guangzhou.

The intracellular nucleotide-binding leucine-rich repeat receptor (SlNRC4a) enhances immune signalling elicited by extracellular perception.

Plant recognition and defence against pathogens employs a two-tiered perception system. Surface-localized pattern recognition receptors (PRRs) act to recognize microbial features, whereas intracellular nucleotide-binding leucine-rich repeat receptors (NLRs) directly or indirectly recognize pathogen effectors inside host cells. Employing the tomato PRR LeEIX2/EIX model system, we explored the molecular mechanism of signalling pathways. We identified an NLR that can associate with LeEIX2, termed SlNRC4a (NB-LRR required for hypersensitive response-associated cell death-4). Co-immunoprecipitation demonstrates that SlNRC4a is able to associate with different PRRs. Physiological assays with specific elicitors revealed that SlNRC4a generally alters PRR-mediated responses. SlNRC4a overexpression enhances defence responses, whereas silencing SlNRC4 reduces plant immunity. Moreover, the coiled-coil domain of SlNRC4a is able to associate with LeEIX2 and is sufficient to enhance responses upon EIX perception. On the basis of these findings, we propose that SlNRC4a acts as a noncanonical positive regulator of immunity mediated by diverse PRRs. Thus, SlNRC4a could link both intracellular and extracellular immune perceptions.

Novel mutations and phenotypes of epilepsy-associated genes in epileptic encephalopathies.

Epileptic encephalopathies are severe epilepsy disorders with strong genetic bases. We performed targeted next-generation sequencing (NGS) in 70 patients with epileptic encephalopathies. The likely pathogenicity of variants in candidate genes was evaluated by American College of Medical Genetics and Genomics (ACMG) scoring taken together with the accepted clinical presentation. Thirty-three candidate variants were detected after population filtration and computational prediction. According to ACMG, 21 candidate variants, including 18 de novo variants, were assessed to be pathogenic/likely pathogenic with clinical concordance. Twelve variants were initially assessed as uncertain significance by ACMG, among which 3 were considered causative and 3 others were considered possibly causative after analysis of clinical concordance. In total, 24 variants were identified as putatively causative, among which 19 were novel findings. SCN1A mutations were identified in 50% of patients with Dravet syndrome. TSC1/TSC2 mutations were detected in 66.7% of patients with tuberous sclerosis. STXBP1 mutations were the main findings in patients with West syndrome. Mutations in SCN2A, KCNT1, KCNQ2 and CLCN4 were identified in patients with epileptic infantile with migrating focal seizures; among them, KCNQ2 and CLCN4 were first identified as potential causative genes. Only one CHD2 mutation was detected in patients with Lennox-Gastaut syndrome. This study highlighted the utility of targeted NGS in genetic diagnoses of epileptic encephalopathies and a comprehensive evaluation of the pathogenicity of variants based on ACMG scoring and assessment of clinical concordance. Epileptic encephalopathies differ in genetic causes, and the genotype-phenotype correlations would provide insights into the underlying pathogenic mechanisms.

[Meta analysis of parallel versus perpendicular double plating for distal humerus fracture of type C in adults].

Objective: To evaluate the effects of parallel versus perpendicular double plating for distal humerus fracture of type C. Methods: A standardized comprehensive literature search was performed by PubMed, Embase, Cochrane library, CMB, CNKI and Medline datebase.Randomized controlled studies on comparison between parallel versus perpendicular double plating for distal humerus fracture of type C before December 2015 were enrolled in the study.All date were analyzed by the RevMan 5.2 software. Results: Six studies, including 284 patients, met the inclusion criteria.There were 155 patients in perpendicular double plating group, 129 patients in parallel double plating group.The results of Meta-analysis indicated that there were statistically significant difference between the two groups in complications (OR=2.59, 95%CI: 1.03 to 6.53, P=0.04). There was no significant difference between the two groups in surgical duration (MD=-1.84, 95% CI: -9.06 to 5.39, P=0.62), bone union time (MD=0.09, 95%CI: -0.06 to 0.24, P=0.22), Mayo Elbow Performance Score (MD=0.09, 95%CI: -0.06 to 0.24, P=0.22), Range of Motions (MD=-0.92, 95%CI: -4.65 to 2.81, P=0.63) and the rate of excellent and good results (OR=0.64, 95%CI: 0.27 to 1.52, P=0.31). Conclusion: Both perpendicular and parallel double plating are effective in distal humerus fracture of type C, parallel double plating has less complications.

Stability and strength of transition-metal tetraborides and triborides.

Using density functional theory, we show that the long-believed transition-metal tetraborides (TB(4)) of tungsten and molybdenum are in fact triborides (TB(3)). This finding is supported by thermodynamic, mechanical, and phonon instabilities of TB(4), and it challenges the previously proposed origin of superhardness of these compounds and the predictability of the generally used hardness model. Theoretical calculations for the newly identified stable TB(3) structure correctly reproduce their structural and mechanical properties, as well as the experimental x-ray diffraction pattern. However, the relatively low shear moduli and strengths suggest that TB(3) cannot be intrinsically stronger than c-BN. The origin of the lattice instability of TB(3) under large shear strain that occurs at the atomic level during plastic deformation can be attributed to valence charge depletion between boron and metal atoms, which enables easy sliding of boron layers between the metal ones.

Predicting melanoma metastatic potential by optical and magnetic resonance imaging.

Accurate prediction of tumor metastatic potential would be helpful in treatment planning and in the design of agents that modify the tumor phenotype. We report that three methods that are potentially transferable to the clinic--dynamic contrast enhanced MRI (DCE MRI), T(1rho)-weighted imaging and low temperature fluorescence imaging (that could be performed on biopsy specimens)--distinguished between relatively indolent (A375P) and aggressive (C8161) metastatic human melanoma xenografts in nude mice, whereas T1 and T2 relaxation time measurements did not. DCE MRI data analyzed by the BOLus Enhanced Relaxation Overview (BOLERO) method in conjunction with concurrent measurements of the arterial input function yielded a blood transfer rate constant (Ktrans) which measures perfusion/permeability, that was significantly higher in the core of the indolent tumor than in the core of the aggressive tumor. Histological staining indicated that aggressive tumors had more blood vascular structure but fewer functional vascular structure than indolent tumors. Indolent tumors exhibited T(1rho), values that were significantly higher than those of aggressive tumors at spin-locking frequencies >500 Hz. The mitochondrial redox ratio, Fp/(Fp+NADH), where Fp and NADH are the fluorescence of oxidized flavoproteins and reduced pyridine nucleotides, respectively, of aggressive tumors was much higher (more oxidized) than that of indolent tumors and often showed a bimodal distribution with an oxidized core and a reduced rim. These differences observed between these two types of tumors, one indolent and one aggressive, if generalizable, would be very valuable in predicting human melanoma metastatic potential.

Structure of an acidic phospholipase A(2) from the venom of Deinagkistrodon acutus in a new crystal form.

The three-dimensional structure of an acidic phospholipase A(2) purified from the venom of Deinagkistrodon acutus (Agkistrodon acutus) was determined in a new crystal form by molecular replacement at 0.28 nm resolution with a crystallographic R factor of 21.9% (R-free=25.7%) and reasonable stereochemistry. Being similar to the previous reported crystal form, a significant conformational adaptation of segment 14-23 at the dimer interface was observed. This segment was related to the "interface recognition site" (IRS). It was found that a positively charged residue at position 34 seems to be a common feature for most of hemolytic PLA(2)s belonging to group II. Structural comparison between the two crystal forms showed that NaCl had significant effects on the crystal packing, thus leading to dramatic changes of the unit cell parameters. In the new crystal form, MPD (2-methyl-2, 4-pentanediol) molecules exist in the hydrophobic channel of the enzyme.

Structure of human muscle creatine kinase.

The crystal structure of human muscle creatine kinase has been determined by the molecular-replacement method and refined at 3.5A resolution. The structures of both the monomer and the dimer closely resemble those of the other known structures in the creatine kinase family. Two types of dimers, one with a non-crystallographic twofold symmetry axis and the other with a crystallographic twofold symmetry axis, were found to exist simultaneously in the crystal. These dimers form an infinite "double-helix"-like structure along an unusual long crystallographic 3(1) axis.

Structure of apo-glyceraldehyde-3-phosphate dehydrogenase from Palinurus versicolor.

d-Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) shows cooperative properties for binding coenzymes. The structure of apo-GAPDH from Palinurus versicolor has been solved at 2.0 A resolution by X-ray crystallography. The final model gives a crystallographic R factor of 0.178 in the resolution range 8 to 2 A. The structural comparison with holo-GAPDH from the same species reveals a conformational change induced by coenzyme binding similar to that observed in Bacillus stearothermophilus GAPDH but to a lesser extent. The differences in magnitude during the apo-holo transition between these two enzymes were analyzed with respect to the change of the amino acid composition in the coenzyme binding pocket. In the crystalline state of apo-GAPDH, the overall structures of the subunits are similar to each other; however, significant differences in temperature factors and minor differences in domain rotation upon coenzyme binding were observed for different subunits. These structural features are discussed in relation to the environmental asymmetry of crystallographically independent subunits.

Structure of active site carboxymethylated D-glyceraldehyde-3-phosphate dehydrogenase from Palinurus versicolor.

The structure of active site carboxymethylated D-glyceraldehyde-3-phosphate dehydrogenase from Palinurus versicolor was determined in the presence of coenzyme NAD+ at 1.88 A resolution with a final R-factor of 0.175. The structure refinement was carried out on the basis of the structure of holo-GAPDH at 2.0 A resolution using the program XPLOR. The carboxymethyl group connected to Cys149 is stabilized by a hydrogen bond between its OZ1 and Cys149N, and charge interaction between the carboxyl group and the nicotinamide moiety. The modification of Cys149 induced conformational changes in the active site, in particular, the site of sulphate ion 501 (the proposed attacking inorganic phosphate ion in catalysis), and segment 208-218 nearby. Extensive hydrogen-bonding interactions occur in the active site, which contribute to the higher stability of the modified enzyme. The modification of the active site did not affect the conformation of GAPDH elsewhere, including the subunit interfaces. The structures of the green and red subunits in the asymmetric unit are nearly identical, suggesting that the half-site reactivity of this enzyme is from ligand-induced rather than pre-existing asymmetry. It is proposed that the carboxymethyl group takes the place of the acyl group of the reaction intermediate, and the catalytic mechanism of this enzyme is discussed in the light of a comparison of the structures of the native and the carboxymethylated GAPDH.

Crystallization and preliminary X-ray analysis of human muscle creatine kinase.

Creatine kinase is a key enzyme in the energy homeostasis of cells and tissues with high and fluctuating energy demands. Human muscle MM creatine kinase is a dimeric protein with a molecular weight of approximately 43 kDa for each subunit. It has been crystallized by the hanging-drop vapor-diffusion method using 2-methyl-2, 4-pentanediol as precipitant. The crystals belong to the enantiomorphous space group P6222 or P6422 with cell parameters of a = b = 89.11 and c = 403.97 A. The asymmetric unit of the crystal contains two subunits. A data set at 3.3 A resolution has been collected using synchrotron radiation.

Structure of agkistrodotoxin in an orthorhombic crystal form with six molecules per asymmetric unit.

The structure of agkistrodotoxin crystallized under basic conditions has been determined at 2.8 A resolution by the molecular-replacement technique and refined to a crystallographic R factor of 0.194 and a free R factor of 0.260 with good stereochemistry. The molecular packing in the crystal differs from other PLA(2)s. The six molecules in the asymmetric unit form three dimers linked by Ca(2+) ions in a near-perfect six-ligand octahedral coordinating system. Extensive intermolecular hydrophobic interactions occur at the interfacial recognition site of each neurotoxin molecule, which provides an insight into phospholipase A(2)-membrane interactions. This hydrophobic interaction-induced molecular association along the interfacial recognition site suggests a self-protection mechanism of agkistrodotoxin.

Crystal structure of agkistrodotoxin, a phospholipase A2-type presynaptic neurotoxin from agkistrodon halys pallas.

The crystal structure of agkistrodotoxin containing eight copies of molecules in the asymmetric unit has been determined at 2.8 A resolution to a crystallographic R factor of 0.207 by the molecular replacement technique. Two spatially adjacent regions of agkistrodotoxin molecule, turn 55-61 and stretch 85-91, are remarkably different from those of non-neurotoxic isoforms in conformation and electrostatic characteristics. These regions are likely to be involved in the recognition of agkistrodotoxin towards the specific receptor at the presynaptic membrane. The structural comparison of the interfacial recognition site with non-neurotoxic isoforms reveals a decreased hydrophobicity and lack of residues with bulky hydrophobic side-chains (i.e. Trp) to serve as membrane anchors. This structural feature of agkistrodotoxin may be related to the reduced non-specific binding of the toxin to non-targeted membrane before it arrives at the presynaptic membrane and recognizes the putative receptor. A unique hydrophobic patch including residues I19, P20, F21, A23, F24, M118 and F119 is found on the surface of the molecule near the entrance of the hydrophobic channel which plays an important role in crystal packing. The interaction mode between the patches might give a clue to the binding of the neurotoxin on the membrane. The agkistrodotoxin molecules in the asymmetric unit form two tetramers and each tetramer exhibits a novel "dimer of dimers"-like structure. A molecule-spanning four-stranded antiparallel beta-sheet is formed by the beta-wings of two molecules within a tetramer.