A highly conductive and robust micrometre-sized SiO anode enabled by an in situ grown CNT network with a safe petroleum ether carbon source.

SiO-based materials as lithium-ion anodes have attracted huge attention owing to their ultrahigh capacity. However, they usually undergo severe volume expansion over the repeated lithiation/delithiation processes and have low electronic conductivity, leading to an inferior cycling stability and poor rate capability. In this study, carbon nanotubes in situ grown on the surface of commercially available micro-sized SiO (D50 = 5 µm) were prepared. The conductive network composed of one-dimensional carbon nanotubes could enhance its conductivity and enhance the structural stability during the cycling. The synthesized 3D-SiO@C material demonstrates good long-term cycling stability, with a reversible capacity of up to 687.7 mA h g-1 after 1000 cycles, and it maintains a high reversible capacity of 736.8 mA h g-1, even at a high current density of 1 A g-1.

The Effect of Copper Sulfide Stoichiometric Coefficient and Morphology on Electrochemical Performance.

In this work, CuS, Cu7S4, Cu9S5, Cu7.2S4, and Cu2S with the same morphology were successfully synthesized by the hydrothermal method. According to the calculation, their galvanostatic charge-discharge (GCD) curves were 43.29 (CuS), 86.3 (Cu7S4), 154 (Cu9S5), 185.4 (Cu7.2S4), and 206.9 F/g (Cu2S) at the current density of 1 A/g. The results showed that the energy storage capacity of copper sulfide with the same morphology increased with the increase of the copper sulfide stoichiometric coefficient. At the second part of this work, the agglomerated cuprous sulfide and the microporous cuprous sulfide were successfully prepared, respectively. In addition, the porous spherical cuprous sulfide was annealed to get nano cuprous sulfide. It is found that the specific capacity of the agglomerated structure is the highest, which had reached 206.9 F/g at the current density of 1 A/g, and 547.9 F/g at the current density of 10 A/g after activation.

CHD7 regulates bone-fat balance by suppressing PPAR-γ signaling.

Chromodomain helicase DNA-binding protein 7 (CHD7), an ATP-dependent eukaryotic chromatin remodeling enzyme, is essential for the development of organs. The mutation of CHD7 is the main cause of CHARGE syndrome, but its function and mechanism in skeletal system remain unclear. Here, we show conditional knockout of Chd7 in bone marrow mesenchymal stem cells (MSCs) and preosteoblasts leads to a pathological phenotype manifested as low bone mass and severely high marrow adiposity. Mechanistically, we identify enhancement of the peroxisome proliferator-activated receptor (PPAR) signaling in Chd7-deficient MSCs. Loss of Chd7 reduces the restriction of PPAR-γ and then PPAR-γ associates with trimethylated histone H3 at lysine 4 (H3K4me3), which subsequently activates the transcription of downstream adipogenic genes and disrupts the balance between osteogenic and adipogenic differentiation. Our data illustrate the pathological manifestations of Chd7 mutation in MSCs and reveal an epigenetic mechanism in skeletal health and diseases.

Confined Water Vapor in ZIF-8 Nanopores.

Metal-organic frameworks (MOFs) possess an ordered and size-controllable porous structure, making them an interesting heterogeneous confining environment for water. Herein, molecular dynamics simulations are employed to investigate the structure of confined water vapor in zeolitic imidazolate framework-8 (ZIF-8) nanopores. Water dimers, which are rarely observed in liquid or water vapor, can form in ZIF-8 at room temperature. The six-ring-member gate is the main location of a water dimer in ZIF-8. The terminal methyl and CH groups of the imidazole linker interact with the water dimer by relatively weak hydrogen bonding. The above-presented findings provide a foundation for the elucidation of water confined in ZIF-8 and demonstrate the potential of obtaining low-order clusters of water by MOFs.

CEACAM7 Is an Effective Target for CAR T-cell Therapy of Pancreatic Ductal Adenocarcinoma.

PURPOSE: To investigate whether CEACAM7 represents a novel therapeutic target for treating pancreatic ductal adenocarcinoma (PDAC) and to generate CEACAM7-targeting CAR T cells to test this hypothesis. EXPERIMENTAL DESIGN: We identified CEACAM7 (CGM2), a member of the CEA family of proteins with expression restricted to the colon and pancreas, as a potential CAR T-cell target for PDAC. We probed a panel of PDAC tumor sections as well as patient-derived PDAC cell cultures for CEACAM7 expression. We generated CAR-targeting CEACAM7, and assessed antitumor efficacy of CEACAM7 CAR T cells using in vitro and in vivo models. RESULTS: We show here that CEACAM7 is expressed in a large subset of PDAC tumors, with low to undetectable expression in all normal tissues tested. CEACAM7 is also expressed in primary PDAC cultures isolated from patient-derived tumors, with high expression within the cancer stem cell-enriched subset. CAR T cells targeting CEACAM7 are capable of targeting antigen-expressing tumor cells, and mediate remission in patient-derived xenograft tumors. CONCLUSIONS: We identify CEACAM7 as a potential therapeutic target in PDAC and describe the development of CEACAM7-targeted CAR T cells with efficacy against PDAC.

Elevated electrochemical performances enabled by a core-shell titanium hydride coated separator in lithium-sulphur batteries.

To date, the lithium-sulphur battery is still suffering from fast capacity fade and poor rate performance due to its special electrochemical mechanism. The interlayer or separator with conductive coatings is considered effective in inhibiting the shuttle effect. Here, we proposed a novel metal hydride with high conductivity and preferably chose TiH2 as the conductive coating because of its low cost, high conductivity, and good stability in air. The TiH2 powder was prepared by a simple ball-milling method, and the effect of the atmosphere was also investigated. A core-shell heterostructure formed, in which the TiH2 core acted as an electron transfer pathway, and the titanium oxide nano-shell functioned as the absorber for polysulfides. Thus, with the combination of fast electronic transfer and strong absorption ability, the TiH2 coated separator could improve the cycling stability, the rate performances, and the self-discharge rate. The TiH2 separator could increase the capacity of the lower plateau and delay the oversaturation points at high rates, promoting the liquid-solid conversion. It is believed that the promotion resulted from the high conductivity and polysulfide absorption of the TiH2 separator. Although the preparation process still needs further optimization, the core-shell metal hydride provided a novel strategy for designing the heterostructure, which could provide high conductivity and strong absorption ability toward polysulfides simultaneously.

Salivary microbiome in patients undergoing hemodialysis and its associations with the duration of the dialysis.

BACKGROUND: Chronic kidney disease (CKD) patients, especially those with end stage renal disease (ESRD) undergoing hemodialysis (HD), exhibit high prevalence of periodontitis. This cross-sectional study aimed to investigate the periodontal status of HD patients and its relationship with salivary microbiome. METHODS: One hundred eight HD patients and one hundred healthy control individuals were recruited. They were subjected to periodontal examination followed by saliva samples collection for 16S rRNA gene sequencing. RESULTS: The HD patients were with worse periodontal health status, and exhibited higher salivary microbial diversity and lower richness. The periodontal pathogens were significantly enriched in the HD patients. The inferred functional analyze showed microbes enriched in the HD patients were mainly related to metabolism. Despite the periodontal status and overall structure of the microbiome were not significantly altered as the HD duration prolonged, the abundance of Lachnospiraceae [G-2] sp. |HMT_096| is positively correlated with the duration of HD and the community periodontal index (CPI). Five OTUs (operational taxonomic units) belonging to the phyla Firmicutes were enriched as the duration prolonged, and four OTUs originated from the phyla Proteobacteria were negatively related with the CPI index. ESRD patients undergoing HD exhibited microbiota structural, compositional and functional differences compared with the healthy controls. And the species changed as the duration of hemodialysis prolonged. CONCLUSIONS: End stage renal disease changes salivary microbiome and is a risk factor for oral dysbiosis.

Saliva: potential diagnostic value and transmission of 2019-nCoV.

2019-nCoV epidemic was firstly reported at late December of 2019 and has caused a global outbreak of COVID-19 now. Saliva, a biofluid largely generated from salivary glands in oral cavity, has been reported 2019-nCoV nucleic acid positive. Besides lungs, salivary glands and tongue are possibly another hosts of 2019-nCoV due to expression of ACE2. Close contact or short-range transmission of infectious saliva droplets is a primary mode for 2019-nCoV to disseminate as claimed by WHO, while long-distance saliva aerosol transmission is highly environment dependent within indoor space with aerosol-generating procedures such as dental practice. So far, no direct evidence has been found that 2019-nCoV is vital in air flow for long time. Therefore, to prevent formation of infectious saliva droplets, to thoroughly disinfect indoor air and to block acquisition of saliva droplets could slow down 2019-nCoV dissemination. This review summarizes diagnostic value of saliva for 2019-nCoV, possibly direct invasion into oral tissues, and close contact transmission of 2019-nCoV by saliva droplets, expecting to contribute to 2019-nCoV epidemic control.

[Effectiveness comparison between the paratricipital approach and the chevron olecranon V osteotomy approach in the treatment of type C3 distal humeral fractures].

Objective: To compare the effectiveness between paratricipital approach and chevron olecranon V osteotomy approach for the treatment of type C3 (AO/OTA) distal humeral fractures and investigate the details of operation. Methods: Between April 2010 and September 2016, 36 type C3 (AO/OTA) distal humeral fractures were treated with open reduction and bicolumnar orthogonal locking plating fixation by paratricipital approach and chevron olecranon V osteotomy approach respectively. The patients were divided into 2 groups by approach, there were 17 cases in paratricipital group (group A) and the bicolumns and distal humeral joint surface were exposed by traction of triceps and olecranon, and the distal humeral joint surface of the 19 cases in chevron olecranon V osteotomy group (group B) were exposed by osteotomy of the olecranon and reversing of triceps. There was no significant difference in gender, age, dominant side, interval between injury and surgery, causes of injury between 2 groups ( P>0.05). Patients were followed up, the postoperative range of motion of elbow joint, strength, pain, and stability in 2 groups were documented and compared; the elbow joint function was evaluated according to Mayo elbow performance score (MEPS). Results: The operation time of group A [(115.0±10.4) minutes] was less than that of group B [(121.0±12.3) minutes], but there was no significant difference ( t=­1.580, P=0.123). All patients in 2 groups got over 1 year follow-up and there was no significant difference of the follow-up time between 2 groups ( t=­0.843, P=0.405). There was 1 case of heterotopic ossification in each group; 1 case of incision infection in group A and 1 case of incision superficial infection in group B, and were cured after 2 weeks of intravenous antibiotics administration. There was no other operative complications in the 2 groups. At 3 months after operation, all the distal humerus healed. At last follow-up, the elbow flexion extension range of groups A and B were (102.0±12.6)° and (99.5±10.1)° respectively, showing no significant difference ( t=­0.681, P=0.501). The MEPS scores of groups A and B were 82.9±7.3 and 81.3±7.2 respectively, showing no significant difference ( t=0.670, P=0.507); and the evaluation grade also showed no significant difference between 2 groups ( Z=­0.442, P=0.659). Conclusion: By paratricipital approach and proper traction of the olecranon, the distal humeral articular surface can be exposed in the operation of type C3 distal humeral fractures, followed with same stable fixation after reduction, the effectiveness is equal to by chevron olecranon V osteotomy approach.

Smoking May Lead to Marginal Bone Loss Around Non-Submerged Implants During Bone Healing by Altering Salivary Microbiome: A Prospective Study.

BACKGROUND: This prospective and controlled study elucidates the impact of smoking on the salivary microbiome and its further influence on marginal bone loss (MBL) around an implant during a 3-month bone-healing period. METHODS: Saliva samples were collected preoperatively from 20 periodontally healthy patients with single-tooth replacement in the posterior mandible (smokers [n = 10] and non-smokers [n = 10]). Sequencing of 16S recombinant RNA gene amplicons was used to characterize the salivary microbiome. Each patient received implant surgery after oral clinical assessment, and MBL around the implant was measured during a 3-month healing period. RESULTS: In total, 871,389 sequences were compared against the Human Oral Microbiome Database for bacterial identification. Microbial signatures of smokers exhibited lower diversity and richness, with a significant decrease in uncultured species. The phyla Gracilibacteria and Saccharibacteria showed a significant decrease in smokers. The genera Streptococcus, Lachnoanaerobaculum, Stomatobaculum, and Eubacterium were significantly increased in smokers, whereas Selenomonas, Selenomonas [G-3], and Catonella were significantly decreased. Specifically, Porphyromonas gingivalis was significantly more abundant in smokers, which was positively related to the severity of MBL during bone healing. CONCLUSIONS: Smoking shapes the salivary microbiome in states of clinical health, and further may influence MBL during bone healing by creating high at-risk-for-harm communities. Understanding of the distinctly divergent oral microbiome in smokers and non-smokers is a base for personalized therapeutics for this high-risk cohort and also a base for further study on the pathologic mechanisms.

Marginal bone loss around non-submerged implants is associated with salivary microbiome during bone healing.

Marginal bone loss during bone healing exists around non-submerged dental implants. The aim of this study was to identify the relationship between different degrees of marginal bone loss during bone healing and the salivary microbiome. One hundred patients were recruited, and marginal bone loss around their implants was measured using cone beam computed tomography during a 3-month healing period. The patients were divided into three groups according to the severity of marginal bone loss. Saliva samples were collected from all subjected and were analysed using 16S MiSeq sequencing. Although the overall structure of the microbial community was not dramatically altered, the relative abundance of several taxonomic groups noticeably changed. The abundance of species in the phyla Spirochaeta and Synergistetes increased significantly as the bone loss became more severe. Species within the genus Treponema also exhibited increased abundance, whereas Veillonella, Haemophilus and Leptotrichia exhibited reduced abundances, in groups with more bone loss. Porphyromonasgingivalis, Treponemadenticola and Streptococcus intermedius were significantly more abundant in the moderate group and/or severe group. The severity of marginal bone loss around the non-submerged implant was associated with dissimilar taxonomic compositions. An increased severity of marginal bone loss was related to increased proportions of periodontal pathogenic species. These data suggest a potential role of microbes in the progression of marginal bone loss during bone healing.

Effect of Different Titanium Surfaces on Maturation of Murine Bone Marrow-Derived Dendritic Cells.

Dendritic cells (DCs) play a pivotal role in the host response to implanted biomaterials. Osseointegration of titanium (Ti) implant is an immunological and inflammatory-driven process. However, the role of DCs in this complex process is largely unknown. This study aimed to investigate the effect of different Ti surfaces on DC maturation, and evaluate its subsequent potential on osteogenic differentiation of preosteoblasts. Murine bone marrow-derived DCs were seeded on Ti disks with different surface treatments, including pretreatment (PT), sandblasted/acid-etched (SLA) and modified SLA (modSLA) surface. Compared with DCs cultured on PT and SLA surfaces, the cells seeded on modSLA surface demonstrated a more round morphology with lower expression of CD86 and MHC-II, the DC maturation markers. Those cells also secreted high levels of anti-inflammatory cytokine IL-10 and TGF-ß. Notably, addition of conditioned medium (CM) from modSLA-induced DCs significantly increased the mRNA expression of Runx2 and ALP as well as ALP activity by murine preosteoblast MC3T3-E1 cells. Our data demonstrated that Ti disks with different surfaces lead to differential DCs responses. PT and SLA surfaces induce DCs mature, while DCs seeded on modSLA-Ti surface maintain an immature phenotype and exhibit a potential of promoting osteogenic differentiation of MC3T3-E1 cells.

[Dual-planar osteotomy and lateral column anatomic locking plate fixation in the treatment of adult cubitus varus deformity].

Objective: To explore the effectiveness of distal humeral dual-planar osteotomy followed with distal humeral lateral column anotomical locking plate fixation in the treatment of adult cubitus varus deformity combined with flexion restriction. Methods: The clinical data of 6 adult patients with cubitus varus deformity and flexion restriction treated with dual-planar osteotomy and internal fixation between April 2012 and September 2014 were reviewed. There were 3 males and 3 females with an average age of 22.2 years (range, 18-35 years). All the patients had history of elbow injury in childhood, the age being injured was 6.5 years on average (range, 2-13 years). There was no nerve injury, elbow strength weak, or unstable complications before admission. The preoperative elbow flexion was (107.50±5.24)°, elbow extension was (-12.17±3.48)°; the carring angle was (-19.50±4.46)°, the contralateral elbow carrying angle was (11.50±2.67)°; the length of humerus was (0.42±0.38) cm shorter than the unaffected humerus. The postoperative carrying angles, elbow flexion and extension, and humerus length were recorded. The modified Laupattarakasem criteria in which the comparison of bilateral elbow range of motion excluded was used to evaluate the results. Results: Primary healing of incision was got in all patients and there was no early postoperative complications. All the patients were followed up 19-27 months (mean, 20.8 months). During the follow-up, there was no complication such as loosening and breakage of the internal fixators and all fractures were healed within 3 months after operation. At last follow-up, the elbow flexion was (124.17±5.85)°, the elbow extension was (0.83±2.04)°, the carrying angle was (12.00±4.19)°, and the humerus shortening was (1.88±0.45) cm, all showing significant difference when compared with preoperative ones ( t=-6.742, P=0.001; t=-11.068, P=0.000; t=-20.400, P=0.000; t=-13.914, P=0.000). According to the modified Laupattarakasem criteria, 1 case was excellent, 4 were good, and 1 was fair with an excellent and good rate of 83.3%. Conclusion: Normal carrying angle can be restored and elbow flexion can be increased by coronal closing wedge and sagittal trapezoid dual-planar osteotomy, single lateral anatomical locking plate fixation is available for early mobilization.

[Lateral closing wedge osteotomy and modified cross pinning with external tension band fixation in the treatment of cubitus varus deformity in childrenLateral closing wedge osteotomy and modified cross pinning with external tension band fixation in the treatment of cubitus varus deformity in children].

OBJECTIVE: To explore the therapeutic effects of distal humeral lateral closing wedge osteotomy followed by modified pinning combined with external tension band fixation in the treatment of cubitus varus deformity in children. METHODS: Total 26 adult patients with cubitus varus deformity were treated by operation from March 2011 to June 2015, 15 patients were boys and the other 11 patients were girls, ranging in age from 4 to 13 years, with an average of 7.8 years. The cubitus varus angel ranged from 11 degrees to 24 degrees, with a mean(17.50±6.73) degrees, 3 patients complicated more than 10 degrees constriction of flexion. Lateral closing wedge osteotomy retaining the medial 3 to 4 mm intact cortex by lateral elbow approach was applied in these 26 patients. The wedge defect were closed and fixed by crossing pinning. The lateral column compression was achieved with external tension band(the crossing pins were bended laterally and the pin ends were hooked mutually). The pre-operative, post-oparetive and contralateral carrying angles were compared and Laupattarakasem criteria was used to evaluate the results at follow-up. RESULTS: All the patients got bony union 2 months after operation and there was no infection or nerve palsy. The average follow-up period was 18.8 months (ranged, 13 to 29 months). The carrying angle was restored to(11.50±3.17) degrees(ranged, 8 to 14 degrees). According to the Laupattarakasem evaluation criteria, 14 patients got an excellent result, 13 good and 1 fair. CONCLUSIONS: Normal carrying angle and elbow flexion could be restored by lateral closing wedge osteotomy, and stable fixation could be achieved with crossing pinning and external tension band, which is available for early mobilization.

Comparative Analysis of Immune Repertoires between Bactrian Camel's Conventional and Heavy-Chain Antibodies.

Compared to classical antibodies, camel heavy chain antibodies (HCAbs) are smaller in size due to lack of the light chain and the first constant domain of the heavy chain (CH1 region). The variable regions of HCAbs (VHHs) are more soluble and stable than that of conventional antibodies (VHs). Even with such simple structure, they are still functional in antigen binding. Although HCAbs have been extensively investigated over the past two decades, most efforts have been based upon low throughput sequence analysis, and there are only limited reports trying to analyze and describe the complete immune repertoire (IR) of camel HCAbs. Here we leveraged the high-throughput data generated by Next Generation Sequencing (NGS) of the variable domains of the antibody heavy chains from three Bactrian camels to conduct in-depth comparative analyses of the immunoglobulin repertoire. These include analyses of the complementary determining region 3 (CDR3) length and distribution, mutation rate, antibody characteristic amino acids, the distribution of the cysteine (Cys) codons, and the non-classical VHHs. We found that there is higher diversity in the CDR2 than in the other sub-regions, and there is a higher mutation rate in the VHHs than in the VHs (P < 0.05). In addition to substitutions at amino acid (AA) residue positions NO.49/50/52 between VH and VHH clones, we also observed other substitutions at the positions NO.40/54/57/96/101 that could lead to additional structural alterations. We also found that VH-derived VHH clones, referred to as non-classical VHH clones in this study, accounted for about 8% of all clones. Further, only 5%-10% clones had the Trp > Arg AA substitution at the first position of framework 4 for all types of clones. We present, for the first time, a relatively complete picture of the Bactrian camel antibody immune repertoire, including conventional antibody (Ab) and HCAbs, using PCR and in silico analysis based on high-throughput NGS data.

GDF11 decreases bone mass by stimulating osteoclastogenesis and inhibiting osteoblast differentiation.

Osteoporosis is an age-related disease that affects millions of people. Growth differentiation factor 11 (GDF11) is a secreted member of the transforming growth factor beta (TGF-ß) superfamily. Deletion of Gdf11 has been shown to result in a skeletal anterior-posterior patterning disorder. Here we show a role for GDF11 in bone remodelling. GDF11 treatment leads to bone loss in both young and aged mice. GDF11 inhibits osteoblast differentiation and also stimulates RANKL-induced osteoclastogenesis through Smad2/3 and c-Fos-dependent induction of Nfatc1. Injection of GDF11 impairs bone regeneration in mice and blocking GDF11 function prevents oestrogen-deficiency-induced bone loss and ameliorates age-related osteoporosis. Our data demonstrate that GDF11 is a previously unrecognized regulator of bone remodelling and suggest that GDF11 is a potential target for treatment of osteoporosis.

Estrogen Deficiency Leads to Further Bone Loss in the Mandible of CKD Mice.

BACKGROUND: Chronic kidney disease (CKD) has been regarded as a grave public health problem. Estrogen is a critical factor for both renal protection and bone remodeling. Our previous study demonstrated that CKD impairs the healing of titanium implants. The aim of this study was to investigate the effects of estrogen deficiency on the mandibular bone in CKD mice. METHODS: Forty eleven-week-old female C57BL mice were used in this study. Uremia and estrogen deficiency were induced by 5/6 nephrectomy and ovariectomy (OVX), respectively. After 8 weeks, the mice were sacrificed, and their mandibles were collected for micro-CT analysis and histological examination. RESULTS: All the mice survived the experimental period. Serum measurements confirmed a significant increase in BUN in the CKD group that was further increased by OVX. OVX led to significant decreases in both the BV/TV and cortical thickness of the mandibular bone in CKD mice. CONCLUSION: In summary, our findings indicate that estrogen deficiency leads to further mandibular bone loss in CKD mice.

Delineating the biosynthesis of gentamicin x2, the common precursor of the gentamicin C antibiotic complex.

Gentamicin C complex is a mixture of aminoglycoside antibiotics used worldwide to treat severe Gram-negative bacterial infections. Despite its clinical importance, the enzymology of its biosynthetic pathway has remained obscure. We report here insights into the four enzyme-catalyzed steps that lead from the first-formed pseudotrisaccharide gentamicin A2 to gentamicin X2, the last common intermediate for all components of the C complex. We have used both targeted mutations of individual genes and reconstitution of portions of the pathway in vitro to show that the secondary alcohol function at C-3″ of A2 is first converted to an amine, catalyzed by the tandem operation of oxidoreductase GenD2 and transaminase GenS2. The amine is then specifically methylated by the S-adenosyl-l-methionine (SAM)-dependent N-methyltransferase GenN to form gentamicin A. Finally, C-methylation at C-4″ to form gentamicin X2 is catalyzed by the radical SAM-dependent and cobalamin-dependent enzyme GenD1.

Ultrathin, biomimetic, superhydrophilic layers of cross-linked poly(phosphobetaine) on polyethylene by photografting.

Ultrathin, biomimetic, superhydrophilic hydrogel layers, composed of cross-linked poly(2-methacryloyloxyethyl phosphorylcholine), are formed on low-density polyethylene films via ultraviolet-initiated surface graft polymerization. The layers are 19-58 nm thick as revealed by electron microscopy and have three-dimensional networks; the unique network structure, along with its zwitterionic nature, rather than surface roughness results in superhydrophilicity, that is, the water contact angle around 5°. This superhydrophilicity depends on a variety of factors, including the concentration of the monomer and cross-linker, the type of reaction solvents, the reaction and drying time, the intensity of UV light, and the way of measurement of water contact angles. Superhydrophilicity is obtained under a fixed ratio (e.g., 1/1) of the monomer to cross-linker, a reaction time over 120 s, a short drying time, (75%) ethanol as the reaction solvent, and low-intensity UV light, largely because these factors together generate optimal three-dimensional networks of cross-links.

Specificity and promiscuity at the branch point in gentamicin biosynthesis.

Gentamicin C complex is a mixture of aminoglycoside antibiotics used to treat severe Gram-negative bacterial infections. We report here key features of the late-stage biosynthesis of gentamicins. We show that the intermediate gentamicin X2, a known substrate for C-methylation at C-6' to form G418 catalyzed by the radical SAM-dependent enzyme GenK, may instead undergo oxidation at C-6' to form an aldehyde, catalyzed by the flavin-linked dehydrogenase GenQ. Surprisingly, GenQ acts in both branches of the pathway, likewise oxidizing G418 to an analogous ketone. Amination of these intermediates, catalyzed mainly by aminotransferase GenB1, produces the known intermediates JI-20A and JI-20B, respectively. Other pyridoxal phosphate-dependent enzymes (GenB3 and GenB4) act in enigmatic dehydroxylation steps that convert JI-20A and JI-20B into the gentamicin C complex or (GenB2) catalyze the epimerization of gentamicin C2a into gentamicin C2.