桑蚕丝素蛋白初始结构对其矿化作用的影响

以碱金属离子诱导桑蚕丝素蛋白溶液发生构象转变, 研究了蛋白质初始结构对其矿化作用的影响. FT-IR, XRD和SEM等测试结果显示, 未经任何处理的桑蚕丝素蛋白溶液矿化后形成片状复合物, 其无机相以二水磷酸氢钙(DCPD)为主; 而经过K^＋和Na^＋金属离子处理后, 桑蚕丝素溶液的结构由无规线团/螺旋构象向β-折叠发生转变, 矿化后成纤维状, 并相互结合呈现纳米级的三维多孔结构, 其无机相以热力学稳定的羟基磷灰石(HA)为主. 可以认为, 丝素蛋白结构转化为较伸展的β-折叠后, 使得更多的亲水基团暴露在外面, 在丝素蛋白分子不断凝聚成纤过程中, HA结晶快速生长并附着在这些微纤上, 最终形成纤维状的丝素蛋白/HA复合物. 该结果为阐明蛋白质的生物矿化过程及其调控机理提供了理论依据, 同时可以从矿化复合物的形成来反映这些微量元素可能对骨组织形成的影响, 为临床骨组织的修复提供一定的参考.     

铁和锰对桑蚕丝蛋白构象转变的影响

采用电感耦合等离子体质谱和原子吸收光谱对桑蚕丝腺体和蚕茧丝中Fe和Mn的含量进行表征, 同时采用拉曼光谱研究Fe(III)和Mn(II)对高浓度再生桑蚕丝蛋白水溶液中丝蛋白构象的影响. 研究结果表明, 桑蚕丝纤维中Fe的含量高于其在丝腺体中的含量, 而Mn的含量则相反. 在丝腺体中, Fe的含量从丝腺体的后部到前部逐渐增加; 但Mn含量的变化趋势与Fe不同, 它在丝腺体中部的含量最低. Fe(III)能够诱导丝蛋白的构象由无规线团和/或螺旋结构向β-折叠转变, 但是Mn(II)对丝蛋白的构象没有明显的影响.     

天然蚕丝与丝素蛋白多孔膜的生物降解性研究

较为详细地研究了经不同条件处理的丝素蛋白多孔膜材料和天然蚕丝在蛋白酶作用下的降解性能以及降解前后材料的微观形貌和结构的变化. 结果表明, 丝素蛋白材料中不同结构(构象)的含量是影响其降解速度的一个重要因素. 对于由再生丝素溶液所制备的材料, 调控其中Silk II结构(β-折叠构象)的比例可能是控制丝素蛋白材料降解速度的有效途径.     

pH值对丝素蛋白构象转变的影响

模仿家蚕吐丝过程中伴随丝素蛋白自然脱水的纤维化过程,研究了再生丝素蛋白在各种pH值的磷酸盐缓冲溶液体系中自然干燥脱水成膜后的构象转变.利用激光拉曼散射光谱及其二维相关光谱,定性分析了丝素蛋白酰胺区(1600～1700cm^-1)散射峰的相关组成及结构.在此基础上,利用¹³CCP-MAS固体核磁共振谱对丝素蛋白丙氨酸C_β峰(δ14.5～22)进行了解析拟合.从而确定了体系中与Silk及Silk构象相关的组成含量与pH值的关系.结果表明,pH=5.2的酸性溶液有利于蚕丝丝素蛋白从Silk向Silk构象转变,而中性与碱性溶液(pH=6.9和8.0)则对丝素蛋白的构象转变影响甚小.     

金属离子导致的丝素蛋白的构象转变

蚕丝和蜘蛛丝的优异力学性能一直是科学家们关注的课题^[1-3]。近年来,在蚕丝蛋白结构及其构象方面的研究取得了许多进展^[3-5]。在蚕的腺体中丝素蛋白的构象为silk I（主要是无规线团为主,还有少量的β－转角,α螺旋等）,而在纤维状的丝中为silk Ⅱ（主要是β折叠）。金属离子在蚕叶丝过程中的作用也一直是一个人们关心的问题。Chen等^[6]在研究丝胶（包附在丝素蛋白表层的另外一种蛋白）时发现,在一定pH条件下,Ni^2 离子通过四配位的螯合作用诱导丝素蛋白β折叠的形成。并且,Viney等^[7]根据电感耦合等离子体（ICP－MS）技术推测Ca^2 的增加能使β折叠的形成加速。     

光谱法研究钙离子对丝素蛋白溶解过程中结构的影响

为研究丝素蛋白在氯化钙溶液溶解过程中结构的阶段性变化特征,通过荧光光谱、紫外可见吸收光谱和拉曼光谱技术探讨了不同溶解时间下钙离子对丝素蛋白结构的影响情况。结果表明,在90℃左右,丝素蛋白与氯化钙溶液(Ca Cl2∶H2O=111∶180,质量比)作用0~30 min的时间段内,随着溶解时间的延长,钙离子逐渐渗透到丝素蛋白分子中,与丝氨酸(Ser)、酪氨酸(Tyr)侧链羟基进行配位而形成螯合物,丝素蛋白逐渐溶胀,分子结构变得松弛,埋藏在非结晶区内的色氨酸(Trp)和Tyr也逐渐暴露出来,分子构象由β-折叠向α-螺旋或无规线团转变。此外,外源性荧光探针(ANS)的结果表明,随着溶解时间的延长,丝素蛋白中的疏水性基团逐渐暴露于溶液中。电镜结果表明,丝素蛋白在氯化钙溶液的作用下逐渐由带状转变为片层状,最终呈球状结构。这些结果对调控丝素蛋白在氯化钙溶液中的溶解过程有着较为重要的现实意义。     

纳米TiO2对丝素蛋白膜构象转变的影响

采用溶胶-凝胶法制备纳米TiO2复合丝素膜,并用原子力显微镜、一维红外光谱、二维红外相关光谱对纯丝素膜及复合丝素膜进行了研究。结果表明:纳米TiO2均匀地分散在丝素膜中;纳米粒子与丝素形成了分子间氢键,导致丝素分子的重排;丝素分子链的构象发生了转变,变化顺序是无规线团先于β-折叠、α-螺旋的形成。     

真空浇铸聚苯乙烯薄膜的拉伸力学行为

高分子溶液的浓度从极稀到极浓的转变过程是高分子链从单链体系转变成相互穿透的多链体系的分子凝聚过程 .在极稀溶液中高分子链以无规线团状态孤立地存在于溶剂介质中 ;在良溶剂中是溶涨的无规线团 ,可以设想溶液浓度逐渐增大时 ,有一高分子线团开始相互接触的所谓接触浓度 ;随着浓度进一步增加高分子线团之间就发生交叠而相互穿透 ,这时溶液就转变成物理交联结构的浓溶液 .分子链的互穿程度会随浓度的继续增加而增加 .如果能用一些特殊的实验方法将高分子在不同浓度的溶液中的凝聚状态尽量全部或部分的保留到高分子固体中 ,则所得到的具有…     

再生丝素蛋白-纳米生物活性玻璃复合膜的制备和表征

将再生丝素蛋白(SF)与纳米生物活性玻璃(NBG)粉体复合成膜,制备出一种新型生物材料。采用场发射扫描电镜(FESEM)、红外光谱(FT-IR)、热重分析(TGA)等方法对复合膜结构进行表征。结果表明:NBG均匀分散在丝素膜中,随着NBG含量的增加,复合膜中丝素的构象部分由无规线团或SilkⅠ向SilkⅡ转变,同时力学性能变差。体外生物活性研究表明:复合膜表面沉积出较多的类骨羟基磷灰石(HA),说明其具有较高的生物活性及优良的诱导类骨HA沉积的能力。     

二维相关红外光谱研究再生蚕丝蛋白膜的构象与温度之间的关系

通过二维相关红外光谱,研究了再生蚕丝蛋白膜的构象及其转变与温度之间的关系.实验结果表明,将样品从130℃升温到220℃、或在180℃的恒温过程中,丝素蛋白分子链的构象会发生变化,且不同构象对温度升高过程或180℃恒温过程响应的顺序是无规线团变化先于β-折叠、α-螺旋的形成.     

Generalized two-dimensional correlation analysis of NMR and Raman spectra for structural evolution characterizations of silk fibroin

Generalized two-dimensional (2D) correlation spectroscopy was used to characterize the structural evolution of silk fibroin as the pH changed from 6.8 to 4.8, demonstrating that the conformational transitions of silk fibroin are induced step by step as the pH decreases. 2D homo- and hetero-spectral correlation spectroscopy was used to establish the relationship between information extracted from NMR and Raman spectroscopy. This novel method reveals the structural evolution using two probes with different frequency scales (10(5-9) Hz for nuclear spin motion and 10(12-14) Hz for molecular vibration motion), reflecting the different spatial scale sensitivity to the molecular conformational change. The transition order is identified as silk I state (helix dominant) --> silk I intermediate state --> silk II intermediate state --> silk II state (beta-sheet dominant), as the pH decreases. The results may rationalize the silkworm spinning process, which undergoes the conformational transition steadily from the soluble helix state to the insoluble beta-sheet state as the pH decreases from the posterior to anterior glands.     

Immobilization of glucose oxidase with the blend of regenerated silk fibroin and poly(vinyl alcohol) and its application to a 1,1′- dimethylferrocene-mediating glucose sensor

The structure and properties of the blend of regenerated silk fibroin (RSF) and poly(vinyl alcohol) (PVA) were investigated. The two polymers in the blend are in the state of phase segregation. Infrared (IR) spectra indicate that the RSF in the blend maintains its intrinsic properties, thus, ethanol treatment can transfer silk I structure of RSF to silk II structure. The water absorption property and mechanical property of the blend are improved in comparison with those of RSF. The blend maintains the major merit of RSF, that is, it can immobilize glucose oxidase on the basis of the conformational transition from silk I structure to silk II structure. The properties of the immobilized enzyme are examined. Moreover, the second generation of glucose sensor based on the immobilized enzyme is fabricated and it has a variety of advantages including easy maintenance of enzyme, simplicity of construction, fast response time and high stability.     

Concentration‐dependent conformation transition of regenerated silk fibroin induced by graphene oxide nanosheets incorporation

Regenerated silk fibroin (RSF)/graphene oxide (GO) nanocomposite has been substantially investigated due to its significant multifunctional potential. Here, in combination of micromorphology, crystalline conformation, dynamic mechanical property characterization, and Fourier self‐deconvolution (FSD) quantitative analysis, we investigated the RSF molecular chains conformation transition induced by GO nanosheet incorporation, and its influence on the structural and mechanical properties of solution casted RSF/GO composite films. The GO nanosheet promoted the silk fibroin molecular chains conformation transition from random coil to β‐sheet structure, and a correlation between β‐sheet structure fraction and GO concentration was revealed. The β‐sheet structure fraction increases further improved the dynamic mechanical property of composite films. Moreover, based on nucleation‐dependent aggregation of silk fibroin molecular chains, a mechanism considering the competition effect between GO concentration and its total surface area was proposed to explain the observed concentration‐dependent conformation transition phenomenon. The study improves our understanding on silk fibroin conformation transition process in RSF/GO composite and would provide a valuable reference for the rational design of bioinspired multifunctional materials with enhanced mechanical properties. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1506–1515     

Wet-spinning of Regenerated Silk Fiber fromAqueous Silk Fibroin Solutions: Influence ofCalcium Ion Addition in Spinning Dope on thePerformance of Regenerated Silk Fiber简

Ca（II） ions are added in the spinning dope to adjust the solidification rate of regenerated silk fibroin （RSF） solution during the wet-spinning process since Ca（II） ions are proved to be favorable to maintain the stable silk fibroin network in our previous work. The results show that when Ca（II）/RSF ratios are 1/50 and 1/20, the resulted RSF fibers exhibit good performance with the breaking energy more than 70 kJ/kg. However, higher Ca（II）/RSF ratio （for example, 1/10） hinders the solidification of spinning dope and results in poor RSF fibers. These observations together with earlier papers from this laboratory confirm that to produce tough silk fibers the spinning conditions must allow sufficient time for the adjustment of silk fibroin molecular chains.     

Effect of metallic ions on silk formation in the Mulberry silkworm, Bombyx mori

A protein conformation transition from random coil and/or helical conformation to beta-sheet is known to be central to the process used by silk-spinning spiders and insects to convert concentrated protein solutions to tough insoluble threads. Several factors including pH, metallic ions, shear force, and/or elongational flow can initiate this transition in both spiders and silkworms. Here, we report the use of proton induced X-ray emission (PIXE), inductively coupled plasma mass spectroscopy (ICP-MS) and atomic adsorption spectroscopy (AAS) to investigate the concentrations of six metal elements (Na, K, Mg, Ca, Cu, and Zn) at different stages in the silk secretory pathway in the Bombyx mori silkworm. We also report the use of Raman spectra to monitor the effects of these six metallic ions on the conformation transition of natural silk fibroin dope and concentrated regenerated silk fibroin solution at concentrations similar to the natural dope. The results showed that the metal element contents increased from the posterior part to the anterior part of silk gland with the exception of Ca which decreased significantly in the anterior part. We show that these changes in composition can be correlated with (i) the ability of Mg2+, Cu2+, and Zn2+ to induce the conformation transition of silk fibroin to beta-sheet, (ii) the effect of Ca2+ in forming a stable protein network (gel), and (iii) the ability of Na+ and K+ to break down the protein network.     

蚕腺体内和再生丝素蛋白水溶液的性能研究

用偏光显微镜观察了蚕腺体内和再生丝素蛋白水溶液的流动状态和各向异性现象,用乌氏粘度计测试了其流出时间,并用HAKKE流变仪测试了其粘度。结果发现蚕腺体内和再生丝素蛋白水溶液的性质差别非常大,认为丝素蛋白水溶液在蚕腺体内存在一个逐步熟成的过程。随着丝素蛋白水溶液在腺体内的前移,丝素蛋白分子逐渐沿移动方向取向而呈有序态,最终成为粘度非常大的各向异性的凝胶体,而再生丝素蛋白水溶液是粘度非常低的各向同性溶液。这些差异表明,丝素蛋白水溶液在蚕腺体内的熟成过程是蚕能够吐出优良蚕丝的关键步骤,要想制备出高性能的纤维,在“仿生纺丝”之前,首先要“仿生制备纺丝液”。     

桑蚕丝腺体和丝纤维中金属离子的含量

用不同的测试方法, 即质子诱导X射线发射(PIXE)、电感耦合等离子体质谱(ICP-MS)和原子吸收光谱(AAS)对桑蚕丝腺体和丝纤维中金属元素的含量进行了详细的表征. 结果表明, 在桑蚕丝腺体和丝纤维中含有钠、镁、钾、钙、铜、锌、铁、锰八种金属元素, 同时还可能含有微量的铷和锶. 这些金属元素在丝腺体和各种丝纤维(蚕茧丝、强拉丝和脱胶丝)中的含量都有所变化, 而这些变化可能与之在成丝过程(丝蛋白的构象转变过程)中所起的作用有关.     

时间分辨全反射红外光谱对醋酸诱导丝蛋白构象转变的研究

采用时间分辨全反射红外光谱为主要分析手段, 对醋酸在丝蛋白膜中的扩散过程及其对丝蛋白构象转变机理进行了研究. 结果表明, 醋酸能够诱导丝蛋白构象转变为β-折叠. 醋酸的扩散速率和β-折叠构象的生成速率较为相似, 表明醋酸分子渗透到丝蛋白聚集体中是破坏丝蛋白原有氢键并诱导肽链重排, 进而实现构象转变的一个先决条件. 同时, 通过比较真空干燥处理前后丝蛋白膜的实验结果, 证实了丝蛋白中的水含量是影响醋酸的扩散速度以及丝蛋白多肽链重排速度的一个重要因素.