基质与分析物的摩尔比和激光能量对分析物离子信号的影

介绍了一种基质辅助激光解吸电离的进样方法-气溶胶进样方法．包含基质和分析物的气溶胶粒子在大气压力下直接进入气溶胶飞行时间质谱仪,粒子产生的散射光信号由光电倍增管收集,通过外部的时序电路,给出气溶胶粒子粒径的信息并触发266 nm Nd:YAG激光器,可以同时获得气溶胶粒子的粒径和基质辅助激光解吸电离质谱与其他的液体进样方式相比,它可以实现单粒子进样,因而样品消耗较少．主要研究了基质与分析物的摩尔比和激光能量对分析物离子信号的影响,合适的摩尔比和激光能量分别为50-110:1和200-400μJ．     

多肽和蛋白质酰胺-I带振动频率图的温度依赖性

利用高温分子动力学模拟和红外光谱实验手段,研究了一个基于分子力学力场的酰胺-I带振动频率图的温度依赖性. 结果表明,基于298 K所建立的频率图可以应用上至500 K的分子动力学轨迹,所模拟的红外光谱能够很好地重复88 oC时的实验光谱. 另外还模拟了两个含有天然和非天然氨基酸残基的三肽分子的红外光谱,与实验结果相比得到了较好的符合. 结果表明,所建立的频率图能够用于获得多肽体系在不同温度下的酰胺-I带局域模振动频率及其分布,有助于深入认识多肽的热去折叠物种的红外光谱特征.     

Ultraviolet Photodissociation of Peptides: New Insight on the Mobile Proton Model

In this work, we study the mechanism of peptide photodissociation by ultraviolet irradiation at 193 nm wavelength and discuss the role of ionization proton in this process. We found that substituting the ionization proton for the alkali metal cations (sodium) in the peptide ions results in significant changes of the photodissociation spectra. The experimental data obtained in this work revealed that the photodissociation process can be described using the mobile proton model introduced earlier for peptide collision dissociation. The results can be used in proteomics research for optimization of mass spectrometer’s parameters to increase the efficiency of peptide dissociation and in developing sequence-specific models for peptide fragmentation prediction.     

应用CoMFA研究抗菌肽的三维定量构效关系

采用比较分子场分析(CoMFA)方法对抗菌九肽、抗菌十四肽、抗菌十八肽进行三维定量构效关系(3D-QSAR)分析,建立了预测力强的3D-QSAR模型.结果表明,所建立的3D-QSAR模型对三种抗菌肽均有较好的统计学稳定性及预测能力(抗菌九肽:交叉验证系数q~2=0.537,非交叉验证相关系数r~2=0.961,外部样本检验复相关系数Q_(ext)~2=0.883;抗菌十四肽:q~2=0.502,r~2=0.718,Q_(ext)~2=0.645;抗菌十八肽:q~2=0.550,r~2=0.967,Q_(ext)~2=0.989).三维等势图不仅解释了抗菌肽结构与活性的关系,而且为抗菌肽的进一步合成提供了理论依据.     

The Influence of High Pressure on the Formation of Diketopiperazines And Pyroglutamate in Peptides and Peptide Esters

The effects of pressurization on several short chain peptides were examined. Leucylleucine methyl ester was rapidly degraded under pressure at 60 °C. Results were comparable to the pressure induced degradation of aspartame, meaning that the ester bond is largely high pressure sensitive: The structure of such peptides is consequently modified. Glutamine in model systems underwent cyclization to pyroglutamate under pressure only at conditions unrealistic for industrial purposes: 50 °C, pH 9, and holding times exceeding 30 min. No cyclization of peptides with glutamine at the C-terminus was observed.     

唾液中富组氨酸多肽的免标记快速检测

唾液中含有多种生物活性成分,包含部分可用于疾病诊断的生物标志物。相比于血液和尿液,唾液的收集过程更为简便且其收集过程具有完全无创的优点。唾液代替血液、尿液在无创疾病诊断中的作用已日益显现。富组氨酸多肽是由唾液腺分泌的一类富含组氨酸的小分子阳离子多肽,与口腔健康密切相关。近年研究更表明,唾液富组氨酸多肽的浓度与HIV-1、艾滋病等疾病相关。因此,富组氨酸多肽的检测对于口腔健康监控、疾病诊断等具有重大的意义。根据叠氮基与富组氨酸结构域发生较强的氢键作用后给电子能力减弱的原理,建立了富组氨酸多肽的免标记、快速检测方法。实验结果表明,富组氨酸多肽——Histatin 5与3-叠氮基香豆素相互作用后,荧光强度显著增加,当Histatin 5浓度为0.23～31.05 μmol·L-1时,荧光增加值与浓度呈现很好的线性关系,线性相关系数r=0.994,检出限为72 nmol·L-1(3σ/k)。唾液中常见的游离氨基酸和蛋白质不干扰Histatins 5的测定。本方法已成功地测定了唾液中的富组氨酸多肽,加标回收率在96.7%～111.6%之间,表明本方法具有很好的准确性。与现有的唾液分析方法相比,本方法具有简单快速、成本低的优点,并有望为基于唾液的无创、非侵入性诊断提供新方法。     

An NMR Investigation of the Conformational Effect of Nitroxide Spin Labels on Ala-Rich Helical Peptides

Nitroxide spin labels, in conjunction with electron spin resonance (ESR) experiments, are extensively employed to probe the structure and dynamics of biomolecules. One of the most ubiquitous spin labeling reagents is the methanethiosulfonate spin label which attaches a spin label selectively to Cys residues via a disulfide bond (Cys-SL). However, the actual effect of the nitroxide spin label upon the conformation of the peptide or protein cannot be unambiguously determined by ESR. In this study, a series of 16-residue Ala-rich helical peptides was characterized by nuclear magnetic resonance techniques. The C_αH chemical shift analysis, NOEs, and³J_NHαcoupling constants for peptides with no Cys, free Cys, and Cys-SL (with the N–O group reduced) were compared. These results indicate that while replacement of an Ala with a Cys residue causes a loss of overall helical structure, the Cys-SL residue is helix supporting, as would be expected for a non-β-branched aliphatic amino acid. Thus, the Cys-SL residue does not perturb helical structure and, instead, exhibits helix-stabilizing characteristics similar to that found for Ala, Met, and Leu.     

复合酶水解云南白鱼制备生物活性肽类物质

研究了复合蛋白酶对云南土著白鱼水解的工艺条件。考察了酶用量、温度、pH值、反应时间、底物浓度、复合酶比例等因素对白鱼水解的影响。确定了最佳酶解条件为:复合酶用量(木瓜蛋白酶+风味蛋白酶1∶1)16000U/g,底物浓度30%,温度55℃,pH值7.5,时间4h。在此条件下,水解度达34.12%,氮回收率90.05%。该结果为云南白鱼生产功能食品提供科学依据。     

Destruction of Peptides and Nucleosides in Reactions with Low-Energy Electrons

Mass-spectrometry of negative ions is used to study dissociative electron capture by molecules of several nucleosides, simplest di- and tripeptides, and modified dipeptides. Energy domains and efficiencies of dissociative capture are determined for the objects under study, and threshold energies of several fragmentation processes are estimated. It is shown that cytidine and peptides are stable against fragmentation due to simple bond breaking at electron energies ranging from ~0 to 1 eV.     

Tailored Correlation Spectroscopy for the Enhancement of Fingerprint Cross Peaks in Peptides and Proteins

A new experimental mixing scheme for band-selective Hartmann-Hahn transfer between the H^N and H_α resonances of peptides and proteins is presented. This form of tailored correlation spectroscopy (TACSY) allows enhancement of the sensitivity of specific (H^N-H_α)-fingerprint signals compared to broadband TOCSY experiments. The design criteria as well as experimental applications of the multiple-pulse sequence CABBY-1 are presented.     

Fret Studies of Conformational Changes in Heparin-Binding Peptides

FRET (Förster Resonance Energy Transfer) was applied to study structural properties of heparin-binding peptides containing the sequence XBBBXXBX where ‘X’ represents hydropathic or uncharged and ‘B’ represents basic amino acids. Internally quenched fluorogenic peptides were synthesized containing the fluorescent donor oaminobenzoic acid (o-Abz) and the acceptor dinitrophenyl ethylenediamine (Eddnp) group. Using the CONTIN computational package, distance distributions were recovered from time resolved fluorescence data, associated to end-to-end distances of the peptides. The peptides containing three or four repeat units have random structure in aqueous medium, and the interaction with low molecular weight heparin stabilized short end-to end distances. Experiments in water/trifluoroethanol (TFE) mixtures showed changes in distance distributions compatible with compact conformations stabilized above 40 % volume content of TFE in the mixture. Similar changes in distance distributions were also observed for the peptides in interaction with SDS micelles in aqueous suspensions and circular dichroism data revealed alpha-helix formation in the peptides in interaction with heparin, SDS micelles or the co-solvent TFE. The process is dependent on electrostatic and hydrogen bond interactions and the end-to-end distances obtained are smaller than expected for the peptides in linear α-helix conformation, indicating the occurrence of structural arrangements leading to additional decrease in the distances.     

Illuminate Proteins and Peptides by Elemental Tag for HPLC-ICP-MS Detection

Abstract

High-performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC-ICP-MS) is becoming a significant complementary technique of HPLC–molecular mass spectrometry for proteins and peptides quantification. However, the naturally occurring heteroelements inside proteins and peptides, such as sulfur, phosphor, and selenium, are not sensitive enough in ICP-MS for low-abundance proteins and peptides, due to their low ionization efficiency or polyatomic spectral interference. In order to make the low-abundance proteins and peptides “visible” by HPLC-ICP-MS, a foreign elemental tag can be employed. The foreign elemental tags are highly sensitive in ICP-MS and almost absent in common biological matrices, which leads to significantly low limits of detection. This review summarizes the major applications of elemental tags in combination with HPLC-ICP-MS detection. The organic mercury tags, iodine tags, ferrocene tags, and macrocyclic metal chelate complex tags are discussed in detail. The recent development of HPLC-ICP-MS in combination with elemental tags demonstrates the great potential in sensitive and accurate proteins and peptides quantification.     

A Multifunctional Fluorescence Probe for the Detection of Cations in Aqueous Solution: the Versatility of Probes Based on Peptides

We synthesized a tetra-functional fluorescence probe based on dansyl and peptide motif, dansyl-Gly-Trp (DGT, 1), that efficiently bound several metal ions and showed distinguishing optical properties. The probe 1 could respond to Hg²⁺ with enhanced and blue-shifted fluorescence emission but to Cu²⁺ with obvious fluorescence quenching. In addition, 1 was sensitive to pH ranging from 2.0 to 5.0 and precipitated in the presence of Pb²⁺ at neutral conditions. The combination of these intrinsic properties with the selective responses to different chemical inputs allows this system to be implemented as an ionic switch. Furthermore, 1 could penetrate the cell membrane and accumulated well in intracellular region. The underlying mechanisms of the probe to different kind of metal ion were explored successfully by using either ¹H NMR, NOESY, electron paramagnetic resonance (EPR) or FT-IR spectra. In addition, to investigate the binding model of 1/Hg²⁺ and 1/Cu²⁺, simulations were also performed by using density functional theory (DFT) and reasonable binding configurations were achieved for these two complexes.     

Probing Membrane Surfaces and the Location of Membrane-Embedded Peptides by C MAS NMR Using Lanthanide Ions

A simple but efficient ¹³C MAS NMR method is presented for the determination of the location of embedded molecules such as peptides relative to biological membrane surfaces by exploiting the interaction with paramagnetic lanthanide ions. Using various aqueous Dy³⁺ concentrations a distance-dependent differential paramagnetic quenching of NMR lipid resonance intensities for specific carbon sites was observed, with residues at the bilayer surface quenched effectively and hydrophobic sites unaffected by Dy³⁺. Tested on the membrane-embedded 50 residue long M13 coat protein, ¹³C labeled at its Val-29 and Val-31 residues, no paramagnetic quenching was observed for the peptide resonances by Dy³⁺, suggesting that Val-29 and Val-31 are not in close proximity to the bilayer interface, but buried deeply inside the hydrophobic region of the lipid bilayer.     

双肽、多肽物质和蛋白质的紫外共振拉曼光谱研究现状

本文介绍了紫外共振拉曼光谱技术在双肽、多肽物质和蛋白质二级结构研究的现状和进展，双肽物质ＮＭＡ和ＧＬＹ—ＧＬＹ水溶液光异构化过程的紫外共振拉曼光谱研究，简述了紫外共振拉曼光谱实验技术要点。     

水化磷脂层中蛋白质和多肽的高分辨固体核磁共振波谱学

有序样品的固体核磁共振(NMR)已快速发展成测定蛋白质和多肽在“仿真”水化磷脂层中高分辨结构的重要谱学方法. 由于与膜相连的蛋白质和多肽的结构、动力学和功能往往都和其周边自然环境密切相关,因此人们把蛋白质和多肽有序排列于水化磷脂层中进行固体NMR测量, 从而获得与取向相关的各向异性自旋相互作用. 这些取向约束可作为结构参数重构蛋白质在水化磷脂层中的高分辨三维结构. 近十年来在样品制备,NMR探头和实验方法方面的显著发展,极大地促进了有序样品的固体NMR的发展,并使之成为测定与膜相连的蛋白质和多肽结构的有效方法. 该综述介绍有序样品的固体NMR谱学方法,并总结此领域里的最新研究进展.     

Peptides adsorption on TiO2 and Au: Molecular organization investigated by NEXAFS, XPS and IR

We present a spectroscopic study of the structure of two peptides deposited on Au and TiO₂:

- PeptA, (EAK16-RGD) bringing the adhesive RGD sequence linked to EAK16;

- PeptB, having RGD linked to a “scrambled” sequence of the EAK16 peptide.

Previously reported NEXAFS investigations on thin films of the self-assembling peptide EAK16 deposited on Au and TiO₂, revealed molecular order and orientation for both substrates.IR spectra show a β-sheet conformation for PeptA and a random structure for PeptB. Angular-dependent NEXAFS measurements reveal an ordered structure with preferential molecular orientation only for PeptA. XPS analysis indicates that PeptA is adsorbed on TiO₂ in a larger amount than PeptB.     

The Versatility of Combining FRET Measurements and Molecular Mechanics Results for Determining the Structural Features of Ordered Peptides in Solution

Combination of fluorescence resonance energy transfer (FRET) measurements with molecular mechanics results makes it possible to determine the most relevant structural features of a series of short, ordered L-(Me) Val-based peptides [(Me) Val = C-methylvaline] in methanol solution.     

Assembly of Nanoconjugates as New Kind Inhibitor of the Aggregation of Amyloid Peptides Associated with Alzheimer's Disease

The inhibition of amyloid‐β (Aβ) aggregation has been regarded as the primary therapeutic strategy for Alzheimer's diseases (AD). Currently, many kinds of amyloid inhibitors have been explored, but these inhibitors have their own drawbacks. This study proposes and demonstrates a new kind of inhibitor in this work by making use of protease endowed with high selectivity to prevent Aβ aggregation. To do this, a nanoconjugate that is composed of chymotrypsin, Aβ aptamer, and gold nanoparticle is designed and fabricated. The nanoconjugate can actively capture Aβ through interaction between the aptamer and Aβ, and destroy the target peptides through proteolysis mediated by the adjacent protease molecules. Compared with the conventional inhibitors that only passively bind with Aβ, this new kind of inhibitor may provide a novel insight to control Aβ aggregation. The multivalent binding and efficient enzymatic reaction toward Aβ may also enable a more complete clearance of Aβ, which might achieve a better treatment effect for AD in the future.