The polyketide cyclase RemF from Streptomyces resistomycificus contains an unusual octahedral zinc binding site

RemF is a polyketide cyclase involved in the biosynthesis of the aromatic pentacyclic metabolite resistomycin in Streptomyces resistomycificus. The enzyme is a member of a structurally hitherto uncharacterized class of polyketide cyclases. The crystal structure of RemF was determined by SAD and refined to 1.2 Å resolution. The enzyme subunit shows a β-sandwich structure with a topology characteristic for the cupin fold. RemF contains a metal binding site located at the bottom of the predominantly hydrophobic active site cavity. A zinc ion is coordinated to four histidine side chains, and two water molecules in octahedral ligand sphere geometry, highly unusual for zinc binding sites in proteins.     

多孔陶瓷吸附固定纤维堆囊菌发酵制备埃博霉素

由纤维堆囊菌产生的埃博霉素具有极大药用价值,但因纤维堆囊菌液体环境中聚团非均匀生长限制了埃博霉素的大规模生产。借助多孔陶瓷的多孔结构,可为粘细菌提供固体附着生长面,提高埃博霉素产量。利用造孔剂法制备硅藻土基多孔陶瓷,在优化制备及改性条件后,当30目木屑造孔剂用量为2.5%(质量分数),7 MPa下制得的硅藻土基多孔陶瓷性能良好,孔径集中在5μm,比表面积为23.55 m2/g,孔隙率为32%,机械强度为10.2 MPa;经1.5 mol/L FeCl3改性的多孔陶瓷对纤维堆囊菌的吸附量达36.8 mg/g。在优化固定化发酵条件后,当在300 ml三角瓶中装液量为45 ml,固液比3:5,接种量10%,温度30℃,转速220 r/min,最初pH 7.5,发酵时间为8 d时,埃博霉素的产量达90.2 mg/L,与游离发酵相比提高了近4倍。     

Hip circumduction is not a compensation for reduced knee flexion angle during gait

It has long been held that hip abduction compensates for reduced swing-phase knee flexion angle, especially in those after stroke. However, there are other compensatory motions such as pelvic obliquity (hip hiking) that could also be used to facilitate foot clearance with greater energy efficiency. Our previous work suggested that hip abduction may not be a compensation for reduced knee flexion after stroke. Previous study applied robotic knee flexion assistance in people with post-stroke Stiff-Knee Gait (SKG) during pre-swing, finding increased abduction despite improved knee flexion and toe clearance. Thus, our hypothesis was that hip abduction is not a compensation for reduced knee flexion. We simulated the kinematics of post-stroke SKG on unimpaired individuals with three factors: a knee orthosis to reduce knee flexion, an ankle-foot orthosis commonly worn by those post-stroke, and matching gait speeds. We compared spatiotemporal measures and kinematics between experimental factors within healthy controls and with a previously recorded cohort of people with post-stroke SKG. We focused on frontal plane motions of hip and pelvis as possible compensatory mechanisms. We observed that regardless of gait speed, knee flexion restriction increased pelvic obliquity (2.8°, p < 0.01) compared to unrestricted walking (1.5°, p < 0.01), but similar to post-stroke SKG (3.4°). However, those with post-stroke SKG had greater hip abduction (8.2°) compared to unimpaired individuals with restricted knee flexion (4.2°, p < 0.05). These results show that pelvic obliquity, not hip abduction, compensates for reduced knee flexion angle. Thus, other factors, possibly neural, facilitate exaggerated hip abduction observed in post-stroke SKG.     

Supramolecular coordination complexes as diagnostic and therapeutic agents

The metal-based drugs represented by cisplatin, carboplatin, and oxaliplatin, prevail in cancer treatment, whereas new therapeutics are extremely slow to step into the clinic. Poor pharmacokinetics, multidrug resistance, and severe side effects greatly limit the development of metal-based anticancer drugs. The robustness and modular composition of supramolecular coordination complexes allow for the incorporation of novel diagnostic and therapeutic modalities, showing promising potentials for precise cancer theranostics. In this mini review, we highlight the recent advances in the development of supramolecular coordination complexes as diagnostic and therapeutic agents. The key focuses of these reports lie in searching sophisticated coordination ligands and nanoformulations that can potentially solve the issues faced by current metal-based drugs including imaging, resistance, toxicity, and pharmacological deficiencies.     

A surface molecularly imprinted polymer as chiral stationary phase for chiral separation of 1,1′‐binaphthalene‐2‐naphthol racemates

Acrylamide (AM) was copolymerized with ethylene glycol dimethacrylate (EGDMA) in the presence of (R )‐1,1′‐binaphthalene‐2‐naphthol (BINOL) as the template molecules on the surface of silica gel by a free radical polymerization to produce a chiral stationary phase based on the surface molecularly imprinted polymer (SMIP‐CSP). The SMIP‐CSP showed a much better separation factor (α = 4.28) than the CSP based on the molecularly imprinted polymer (MIP‐CSP) without coating on the silica gel (α = 1.96) during the chiral separation of BINOL enantiomers by high‐performance liquid chromatography. The influence of the pretreatment temperature and the content of the template molecule ((R )‐BINOL) of the SMIP‐CSP, and the mobile phase composition on the separation of the racemic BINOL were systematically investigated.     

Characterization of nutrient status of Halamphora luciae (Bacillariophyceae) using matrix-assisted ultraviolet laser-desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS)

The effects of N and P depletion on the production and structural characterization of the cellular carbohydrate polymers of the estuarine diatom Halamphora luciae in batch culture were examined using matrix-assisted laser desorption-ionization time-of flight mass spectrometry (MALDI-TOF MS) complemented with monosaccharide composition determination and structural analyses by methylation of aqueous extracted product. The MALDI MS analysis of the cells showed a similar profile in control and N- and P-depleted media, with a displacement to higher molecular weight for cells grown in depleted media. In the monosaccharide analyses, both nutrient depletion and culture ageing led to an increase in glucose content, indicating that MALDI-TOF MS in whole cells was detecting the changes in chrysolaminarin. The maxima for the ions from f/2-P and to a lesser extent in f/2-N were displaced to higher m/z values indicating a higher degree of polymerization (DP). Methylation analysis confirmed the presence of chrysolaminarin, a (1→3)-β-d-glucan with branching in C2 and C6, where the glucan backbone had a substitution every four glucose residues. The (1→3)-β-d-glucan was also detected in the cingule by fluorescence with aniline blue.     

Salting-in of neopentane in the aqueous solutions of urea and glycine-betaine

The effects of urea and glycine-betaine (GB) osmolytes on the hydrophobic interactions of neopentane in water have been studied using molecular dynamics simulations. From the study of the potentials of mean force, it is observed that both urea and GB decrease the association and solvation of neopentane. The calculated equilibrium constants show that urea and GB decrease the population of solvent-separated minima of neopentane. The hydrophobic association as well as solvation of neopentane molecules are stabilised by entropy and enthalpy in the mixtures. The radial distribution functions (RDFs) and running coordination numbers of water, urea and GB molecules show that neopentane shows salting-in behaviour in aqueous-GB, aqueous-urea and aqueous-urea-GB mixtures. Neopentane is preferentially solvated by GB in aqueous-GB and preferentially solvated by urea in aqueous-urea-GB solutions. The preferential solvation of neopentane by GB suggests that GB decreases the interaction between neopentane molecules i.e. salting-in of neopentane. The calculated solvation free energies and radial density profiles of neopentane also support the salting-in behaviour of neopentane in the mixtures of these osmolytes.     

Epitope imprinting of iron binding protein of Neisseria meningitidis bacteria through multiple monomers imprinting approach

Epitope imprinting is a promising technique for fabrication of novel diagnostic tools. In this study, an epitope imprinted methodology for recognition of target epitope sequence as well as targeted protein infused by bacterial infection in blood samples of patients suffering from brain fever is developed. Template sequence chosen is a ferric iron binding fbp A protein present in Neisseria meningitidis bacteria. To orient the imprinting template peptide sequence on gold surface of electrochemical quartz crystal microbalance (EQCM), thiol chemistry was utilized to form the self‐assembled monolayer on EQCM electrode. Here, synergistic effects induced by various noncovalent interactions extended by multiple monomers (3‐sulfopropyl methacrylate potassium‐salt and benzyl methacrylate) were used in fabricating the imprinting polymeric matrix with additional firmness provided by N,N‐methylene‐bis‐acrylamide as cross‐linker and azo‐isobutyronitrile as initiator. Extraction of template molecule was carried out with phosphate buffer solution. After extraction of epitope molecules from the polymeric film, epitope molecularly imprinted polymeric films were fabricated on EQCM electrode surface. Nonimprinted polymers were also synthesized in the similar manner without epitope molecule. Detection limit of epitope molecularly imprinted polymers and imprinting factor (epitope molecularly imprinted polymers/nonimprinted polymers) was calculated 1.39 ng mL^?1 and 12.27 respectively showing high binding capacity and specific recognition behavior toward template molecule. Simplicity of present method would put forward a fast, facile, cost‐effective diagnostic tool for mass health care.     

Crystal structure of the trimeric N‐terminal domain of ciliate Euplotes octocarinatus centrin binding with calcium ions

Centrin is a member of the EF‐hand superfamily of calcium‐binding proteins, a highly conserved eukaryotic protein that binds to Ca²⁺. Its self‐assembly plays a causative role in the fiber contraction that is associated with the cell division cycle and ciliogenesis. In this study, the crystal structure of N‐terminal domain of ciliate Euplotes octocarinatus centrin (N‐EoCen) was determined by using the selenomethionine single‐wavelength anomalous dispersion method. The protein molecules formed homotrimers. Every protomer had two putative Ca²⁺ ion‐binding sites I and II, protomer A, and C bound one Ca²⁺ ion, while protomer B bound two Ca²⁺ ions. A novel binding site III was observed and the Ca²⁺ ion was located at the center of the homotrimer. Several hydrogen bonds, electrostatic, and hydrophobic interactions between the protomers contributed to the formation of the oligomer. Structural studies provided insight into the foundation for centrin aggregation and the roles of calcium ions.     

Facile Metal Coordination of Active Site Imprinted Nitrogen Doped Carbons for the Conservative Preparation of Non‐Noble Metal Oxygen Reduction Electrocatalysts

Iron‐ or cobalt‐coordinated heteroatom doped carbons are promising alternatives for Pt‐based cathode catalysts in polymer‐electrolyte fuel cells. Currently, these catalysts are obtained at high temperatures. The reaction conditions complicate the selective and concentrated formation of metal–nitrogen active sites. Herein a mild procedure is introduced, which is conservative toward the carbon support and leads to active‐site formation at low temperatures in a wet‐chemical metal‐coordination step. Active‐site imprinted nitrogen doped carbons are synthesized via ionothermal carbonization employing Lewis‐acidic Mg²⁺ salt. The obtained carbons with large tubular porosity and imprinted N₄ sites lead to very active catalysts with a half‐wave potential (E_1/2) of up to 0.76 V versus RHE in acidic electrolyte after coordination with iron. The catalyst shows 4e^? selectivity and exceptional stability with a half‐wave potential shift of only 5 mV after 1000 cycles. The X‐ray absorption fine structure as well as the X‐ray absorption near edge structure profiles of the most active catalyst closely match that of iron(II)phthalocyanine, proving the formation of active and stable FeN₄ sites at 80 °C. Metal‐coordination with other transition metals reveals that Zn–N_x sites are inactive, while cobalt gives rise to a strong performance increase even at very low concentrations.