CRYSTALLIZATION AND MELTING OF POLY(ETHYLENE OXIDE)CONFINED IN NANOSTRUCTURED PARTICLES WITH CROSS-LINKED SHELLS OF POLYBUTADIENE

Small fixed aggregates of a poly(ethylene oxide)-block-polybutadiene diblock copolymer(PEO-b-PB)in THFsolution were obtained by adding a selective solvent for PB blocks,followed by cross-linking the PB shells.Themorphologies of the nanostructured particles with a cross-linked shell were investigated by atomic force microscopy andtransmission electron microscopy.The average behaviors of the PEO crystallization and melting confined within thenanostructured particles were studied by using differential scanning calorimetry experiments.For the deeply cross-linkedsample(SCL-1),the crystallization of the PEO blocks was fully confined.The individual nanoparticles only crystallized atvery low crystallization temperatures(T_cs),wherein the homogenous primary nucleation determined the overallcrystallization rate.For the lightly cross-linked sample(SCL-2),the confinement effect was T_c dependent.At T_c(?)42℃,thecrystallization and melting behaviors of SCL-2 were similar to those of the pure PEO-b-PB diblock copolymer.At T_c>42℃,SCL-2 could form PEO lamellae thicker than those of the pure PEO-b-PB crystallized at the same T_c.

RNA binding protein BOULE forms aggregates in mammalian testis

Amyloids have traditionally been considered pathologic protein aggregates which contribute to neurodegeneration.New evidence however increasingly suggests that non-pathological amyloids are formed in animals during normal development.Amyloid-like aggregate formation was originally thought to be a conserved feature of animal gametogenesis.This hypothesis was based on findings which suggest that regulated amyloid formations govern yeast meiosis by way of meiosis-specific RNA binding proteins.Additional support came from studies which demonstrate that DAZL,a mammalian gametogenesis-specific RNA binding protein,also forms SDS-resistant aggregates in vivo.Here,we report evidence of aggregated BOULE formations,another DAZ family protein,during sperm development.Data suggest that in mouse testis,BOULE forms SDS-resistant amyloid-like aggregates.BOULE aggregate formation correlates with dynamic developmental expression during spermatogenesis but disappeared in Boule knockout testis.We also mapped essential small region in vitro BOULE aggregations,immediately downstream DAZ repeats,and found that aggregations positively correlated with temperature.We also performed enhanced UV cross-linking immunoprecipitation on BOULE aggregates from mouse testes and found that aggregates bind with a large number of spermatogenesis-related mRNAs.These findings provide insight into the amyloidogenic properties of gametogenesis-specific RNA binding proteins as a conserved feature in mammalian reproduction.Further investigation is warranted to understand the functional significance of BOULE amyloid-like formation during mouse spermatogenesis.

Cross-linkedα-amylase aggregates on Fe3O4 magnetic nanoparticles modified with polydopamine/polyethyleneimine for efficient hydrolysis of starch

In this workα-amylase was immobilized on magnetic Fe3O4 nanoparticles with polyethylenimine(PEI)/polydopamine(PDA)coating or 3-aminopropyl triethoxysilane(APTES)for the first time via adsorption–precipitation–cross-linking.Compared with the freeα-amylase,the resultant magnetic cross-linkedα-amylase aggregates(PEI/PDA-M-CLEAs and N-M-CLEAs)exhibited excellent thermal and storage stability as well as pH stability.After storage at 25°C for 60 days,freeα-amylase only retained 60%of its initial activity,while PEI/PDA-M-CLEAs and N-M-CLEAs retained 80%and 78%of their initial activities,respectively.Furthermore,N-M-CLEAs and PEI/PDA-M-CLEAs showed good reusability.After 6 repeated uses,PEI/PDA-M-CLEAs and N-M-CLEAs still maintained 65%and 62%of their initial activities,respectively.Especially,PEI/PDA-M-CLEAs and N-M-CLEAs exhibited higher starch hydrolysis efficiency than freeα-amylase.The maximum dextrose equivalent(DE)values of starch hydrolysis by PEI/PDA-M-CLEAs and N-M-CLEAs reached 29.24%and 28.79%within 90 min,respectively.However,the maximum DE values of starch hydrolysis by the freeα-amylase was only 27.89%even in 150 min.The magnetic cross-linkedα-amylase aggregates could be introduced as effective biocatalyst for industrial applications in production of maltose syrups.

交联糖化酶聚集体的制备

为了克服游离糖化酶的部分缺点,将游离糖化酶用合适的沉淀剂沉淀后,再用戊二醛作为交联剂进行交联,制备了新型的固定化糖化酶-交联糖化酶聚集体。研究结果表明,糖化酶最适聚集条件为:pH5.6,20℃,5g/L的糖化酶液中加入叔丁醇沉淀,可获得比较理想的糖化酶聚集体;最适交联条件为:向糖化酶聚集体中加入10%戊二醛水溶液交联120min,再经离心、洗涤数次后即得交联糖化酶聚集体,酶活力为游离糖化酶的40.4%。

交联糖化酶聚合体的制备与性质研究

交联糖化酶聚合体是利用硫酸铵沉淀糖化酶,以戊二醛为交联剂对其进行化学交联,制备出的一种无载体固定化糖化酶。本实验对交联糖化酶聚合体的制备和酶学性质进行研究。实验结果表明:交联酶聚合体的最终酶活力为3.15×104U/g干胶,其作用的最适pH4.6,最适反应温度为50℃,Km值为1.75%,当酶保护剂黄原胶的添加量为5.0mg/g时,交联糖化酶聚合体残余酶活力较高,且具有比游离酶更高的热稳定性。

磁响应交联糖化酶聚集体的制备及催化特性

提出了一种采用羧基磁性纳米粒子制备杂化磁响应交联酶聚集体(M-CLEAs)的方法。表面羧基修饰的约10 nm的磁性纳米粒子与酶分子表面的氨基位点通过静电相互作用,形成复合物,在磁场作用下可将磁性纳米粒子-酶复合物从溶液中分离,经戊二醛交联即形成M-CLEAs。传统的表面氨基修饰的磁性纳米粒子与酶需在沉淀剂作用下,从溶液中分离,而后采用戊二醛共交联,而本方法无须沉淀剂,过程更为简化。以糖化酶为对象,对该过程的影响因素(交联时间、pH、酶浓度、戊二醛浓度等条件)进行了探索,并对制得的M-CLEAs的酶学性质进行了较为详细考察。结果表明,最优制备条件为:酶浓度1 mg·ml-1,磁流体浓度10 mg·ml-1,戊二醛浓度0.25%(质量体积比),在pH 6.0下交联反应6 h,最终载酶量可达80 mg·g^(-1)、比活为50 U·mg^(-1)。制得的固定化酶pH稳定性、热稳定性和储存稳定性均显著改善,可实现糖化酶重复使用10次,仍保留接近60%的酶活。

Disulfide Crosslinking-Induced Aggregation:Towards Solid-State Fluorescent Carbon Dots with Vastly Different Emission Colors

Solid-state fluorescent multi-color carbon dots(SFM-CDs),prepared using the same precursor(s)without the need for dispersion in a solid matrix,are highly demanded for a wide range of applications.Herein,we report a microwave-assisted strategy for the prepara-tion of SFM-CDs with blue,yellow and red emissions within 5 min from the same precursors.The as-prepared B-CDs,Y-CDs,and R-CDs possessed bright fluorescence at 425 nm,550 nm,and 640 nm,and photoluminescence quantum yields(PLQYs)of 54.68%,17.93%,and 2.88%,respectively.The structure of SFM-CDs consisted of 5-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyridine-7-carboxylic acid(TPCA)immobilized on the surface of a carbon core,with the size of the carbon core and degree of disulfide crosslinking between CDs both increasing on going from the B-CDs to the R-CDs,as verified by mechanochromic experiments.The excellent solid-state fluorescence performance of the SFM-CDs allowed their utilization as the fluorescent converter layer in multi-color LEDs and white LEDs with a high color rendering index.

3D printed silk-gelatin hydrogel scaffold with different porous structure and cell seeding strategy for cartilage regeneration

Hydrogel scaffolds are attractive for tissue defect repair and reorganization because of their human tissue-like characteristics.However,most hydrogels offer limited cell growth and tissue formation ability due to their submicron-or nano-sized gel networks,which restrict the supply of oxygen,nutrients and inhibit the proliferation and differentiation of encapsulated cells.In recent years,3D printed hydrogels have shown great potential to overcome this problem by introducing macro-pores within scaffolds.In this study,we fabricated a macroporous hydrogel scaffold through horseradish peroxidase(HRP)-mediated crosslinking of silk fibroin(SF)and tyramine-substituted gelatin(GT)by extrusion-based low-temperature 3D printing.Through physicochemical characterization,we found that this hydrogel has excellent structural stability,suitable mechanical properties,and an adjustable degradation rate,thus satisfying the requirements for cartilage reconstruction.Cell suspension and aggregate seeding methods were developed to assess the inoculation efficiency of the hydrogel.Moreover,the chondrogenic differentiation of stem cells was explored.Stem cells in the hydrogel differentiated into hyaline cartilage when the cell aggregate seeding method was used and into fibrocartilage when the cell suspension was used.Finally,the effect of the hydrogel and stem cells were investigated in a rabbit cartilage defect model.After implantation for 12 and 16 weeks,histological evaluation of the sections was performed.We found that the enzymatic cross-linked and methanol treatment SF5GT15 hydrogel combined with cell aggregates promoted articular cartilage regeneration.In summary,this 3D printed macroporous SF-GT hydrogel combined with stem cell aggregates possesses excellent potential for application in cartilage tissue repair and regeneration.

Tightening up the structure, lighting up the pathway:application of molecular constraints and light to manipulate protein folding, self-assembly and function

Chemical cross-linking provides an effective avenue to reduce the conformational entropy of polypeptide chains and hence has become a popular method to induce or force structural formation in peptides and proteins.Recently,other types of molecular constraints,especially photoresponsive linkers and functional groups,have also found increased use in a wide variety of applications.Herein,we provide a concise review of using various forms of molecular strategies to constrain proteins,thereby stabilizing their native states,gaining insight into their folding mechanisms,and/or providing a handle to trigger a conformational process of interest with light.The applications discussed here cover a wide range of topics,ranging from delineating the details of the protein folding energy landscape to controlling protein assembly and function.