纳升电喷雾串联质谱(Q-TOF)测序中Na+加合肽的分析

电喷雾串联质谱测序法是蛋白质组研究中蛋白质鉴定的最有力的手段之一。肽段离子在ESI-Q-TOF中往往以多电荷形式出现(2～4个电荷),其中m／z在500～1000之间带双电荷的离子最适合测序。但这样的肽段很容易和Na+加合,有时加合峰的相对强度比原肽段高很多,有时甚至只有加合峰。Na+加合肽的序列分析比较困难,因数据库查寻不支持Na+加合,且Na+加合是非氨基酸特异的,序列分析中不能按修饰编辑,一旦有一个氨基酸的序列发生偏差,整个肽段序列就不正确。因此,Na+加合肽的序列分析很重要。在Na+加合肽序列分析中,寻找m／z相差22Da的离子,以其为起点分别按m／z从高到低和从低到高进行分析,可得到完整序列,用序列进行数据库检索可鉴定蛋白质,本文用此方法分析了5个Na+加合肽的序列,鉴定5个蛋白质。Na+加合位点分别为丝氨酸S、脯氨酸P和酪氨酸Y。     

肿瘤蛋白D52N-端乙酰化的纳升电喷雾串联质谱分析

小鼠髓系白血病M1细胞经IL-6诱导分化后一系列蛋白质点的表达量发生了变化,其中A点表达量显著增加。MALDI-TOF-MS的肽质量指纹谱鉴定表明A点为肿瘤蛋白D52(tumor protein D52,TP D52)。为进一步确认该结果,对A点进行了ESI-MS/MS分析,测定了3个肽段的序列。Mascot数据库查询结果很肯定地表明该蛋白为TP D52,但只有两个肽段与之匹配。对未匹配肽段的序列分析表明它对应于TP D52N端1-10氨基酸MDRGEQGLLK,其中N端第1个氨基酸甲硫氨酸M发生了乙酰化。分析结果与M乙酰化的规律一致,即当第2个氨基酸是酸性氨基酸D或E时,M很容易发生乙酰化。本研究文首次报道了TP D52的N端乙酰化,其功能需要进一步研究。     

电鳗(Electrophorus electricus)肌肉中两种微白蛋白的氨基酸序列

本文用Sephadex G-50凝胶过滤和DEAE-52离子交换柱层析提纯了电鳗(Electrophorus electricus)肌肉中的两种微白蛋白(parvalbumin)。350g新鲜肌肉可提取100—150mg纯的微白蛋白Ⅰ,等电点为4.25。微白蛋白Ⅱ的含量约为组份Ⅰ的1/5,它的等电点为3.85。根据胰蛋白酶水解所得肽段和溴化氰裂解片段的氨基酸序列,以及微白蛋白一级结构的同源性确定了两种微白蛋白的氨基酸全序列。微白蛋白Ⅰ和微白蛋白Ⅱ的序列有22个氨基酸残基差异,但和Ca~( )离子结合有关的氨基酸残基并无变异。     

亮氨酰-tRNA合成酶的限制性酶解及活性片段的研究

大肠杆菌亮氨酰-tRNA合成酶(LeuRS)经胰蛋白酶限制性酶解,被切去约6k分子量肽段,产生一96k片段。该片段具有与天然酶相同的氨基酸活化反应的动力学常数,但丧失氨酰化活性、tRNA~(Leu)结合活性等由tRNAL~(Leu)参与的一系列活性。N-末端分析表明切去的6k肽段系LeuRS C端部分,该部分是LeuRS结合tRNAL~(Leu)所必需的。本文表明LeuRS的氨基酸活化和氨酰化这两种活性是相互独立并分别处于酶分子不同的结构域。LeuRS C端部分可能是tRNA~(Leu)的结合部分。     

高效毛细管电泳 间接紫外吸收检测法测定食品中的氨基酸

研究了鸟氨酸、脯氨酸和谷氨酰胺的高效毛细管电泳 间接紫外吸收检测的特征。以5　mmol/L 对氨基苯磺酸钠 10 mmol/L KH2PO4(pH 11.5)为运行缓冲液,在分离电压12 kV下,于11 min实现了上述3种氨基酸的基线分离,迁移时间和峰高的相对标准偏差分别小于0.72%和2.0%,检测限分别为6.78,8.71,7.86 mg/L。应用该法测定食品中的氨基酸及各氨基酸在样品中的加标回收率,3种氨基酸的加标回收率为96.8%~104%。     

基于生物质谱技术的磷酰化修饰策略在多肽测序中的应用

该文建立了一种利用磷酰化修饰结合电喷雾质谱(ESI-Q-TOF)测定多肽氨基酸序列的有效方法。利用Atherton-Todd反应,以二丙基亚磷酰酯(DPP)为磷酰化试剂,应用生物质谱技术,对磷酰化修饰后的5种模型肽的磷酰化反应情况进行了系统研究,考察了磷酰化肽的二级质谱特征,并与未经磷酰化反应的肽的二级质谱特征对比。结果表明,经过磷酰化修饰后,肽的二级质谱中的a1离子信号强度明显增加,可以准确鉴定其N端氨基酸;b系列离子信息完整,信号强度增强,使得多肽C ID测序的谱图简单、清晰,有利于肽的氨基酸序列的测定;赖氨酸(K,128.10 u)和谷氨酰胺(Q,128.13 u)两种氨基酸质荷比相近,由于二者磷酰化修饰后的差异性,使其得到准确区分。经过5种已知氨基酸序列的模型肽的磷酰化后结合质谱技术进行氨基酸序列测定验证,结果表明该方法简单、快速、准确,提高了利用质谱技术进行多肽测序的准确度和灵敏度,可为蛋白质组学研究提供有效的技术手段。     

原子转移自由基聚合修饰银丝固定化酶反应器的制备及在蛋白质组鉴定中的应用

针对传统溶液酶解存在的酶解时间较长、酶自切物干扰以及蛋白酶不能重复使用等缺陷,通过电子转移生成催化剂的原子转移自由基聚合法修饰银丝,并以其为载体制备了一种新型的固定化酶反应器。用质谱考察了银丝固定化酶反应器(SW-Trypsin)的酶解效率、重复性和回收率。结果表明:绒毛状聚合物修饰的SW-Trypsin的酶解效率较高,酶解标准蛋白牛血清白蛋白(BSA)20 min后,肽段的氨基酸序列覆盖率可达93%,高于传统溶液酶解方法酶解16 h所得79%的覆盖率。使用该固定化酶反应器于一个月内8次酶解BSA所得的氨基酸序列覆盖率在89%到97%之间,平均覆盖率为94%,显示出良好的稳定性。另外,该固定化酶反应器酶解马心肌红蛋白(MYO)的回收率为87.67%。最后,用SW-Trypsin酶解腾冲嗜热菌全蛋白20 min,所鉴定到的氨基酸序列覆盖率和蛋白数量与同样条件下溶液酶解16 h的结果接近,且零漏切位点肽段的比例更高。加之容易分离的优点,SW-Trypsin在蛋白质组学的应用中具有良好的前景。     

基于LTQ-Orbitrap液相色谱-质谱联用技术的乳源乳清蛋白组分的差异性研究

利用LTQ Orbitrap XL组合型傅立叶变换高分辨质谱系统分析了乳源蛋白主要组分肽指纹图谱。对南方水牛乳与不同来源的乳清蛋白的氨基酸序列研究结果表明,乳清蛋白经酶解后主要为α-乳白蛋白(α-La)和β-乳球蛋白(β-Lg)组分,乳清蛋白肽质指纹谱的分析显示水牛乳与荷斯坦奶乳清蛋白α-La氨基酸发生变异的比率明显少于山羊奶乳清蛋白α-La,说明荷斯坦奶α-La和水牛乳α-La的差异更小,同源性更强;而水牛乳β-Lg与荷斯坦乳β-Lg氨基酸发生变异的部位比率要多于山羊奶,水牛乳β-Lg与山羊奶同源性更强;乳源酪蛋白酶解后的肽段主要组分为αs1-CN,β-CN,κ-N,通过对水牛乳酪蛋白的氨基酸序列的差异性分析,不同品种的乳源酪蛋白的氨基酸序列明显存在差异。与乳清蛋白相比,奶牛品种差异导致乳蛋白发生氨基酸差异现象更显著,酪蛋白的氨基酸序列对比表明,水牛奶酪蛋白与山羊奶酪蛋白比与乳牛酪蛋白的差异更大。     

一个不寻常的人λ-型Bence Jones蛋白(Lee)可变区的氨基酸序列

用限制性胰蛋白酶水解,制备了人λ-型Bence Jones蛋白(Lee)的可变区,用还原并氨乙基化的蛋白质制备了溴化氰裂解片段和胰蛋白酶水解肽,测定各肽段的氨基酸序列并根据Lee蛋白和其它λ-链的同源性定出了Lee轻链可变区的氨基酸全序列。Lee轻链的N末端有二个额外氨基酸残基的延伸。Lee蛋白的个体型(idiotypic)抗体能和另外两个λ-型Bence Jones蛋白MCg λ_Ⅳ和Cap λ_Ⅲ反应。用Chou和Fasman的方法预测Lee轻链可变区二级结构的结果表明:Lee轻链可变区表面上有两个部分和Mcg,Cap的相应部分的结构相同,这是这三个蛋白质在免疫学性质上具有个体型相似性的可能解释。     

爱滋病病毒中肽段的酶促合成

为了进一步研究酶促合成在多肽合成中的实际应用,选择合成了爱滋病病毒(人类免疫缺损病毒,HIV-I)的gp41中氨基酸序列598-609的三个肽段,该部分是HIV-I中的2个抗原决定簇部分,H-Leu-Glg-Leu-Trp-Glg-cgs-Ser-Glg-Lgs-Leu-Ile-Cgs-OH可以作为抗原来检测HIV抗体.     

Studies on Fragmentation of Peptide by Nano-electrospray Ionization Fourier Transform Ion Cyclotron Resonance Multi-stage Tandem Mass Spectrometry

The sequence analysis of peptides was performed by nano-electrospray ionization Fourier transform ion cyclotron resonance tandem mass spectrometry(Nano-ESI-FT-ICR-MSn) and several peptides were chosen as examples. With the aid of the collision induced dissociation(CID), FT-ICR provides not only precise mass/charge ratio, but also structure information of the selected peptides. The fragment ions were identified according to the observed molecular weights and peptide sequence was determined successfully. So Nano-ESI-FT-ICR-MSn is a useful tool for identification of the amino acid sequence of peptides with high confidence. Besides, a pathway for the dehydration of y ions without amino acids containing carboxylic acid under sustained off-resonance irradiation collision-induced dissociation(SORI-CID) condition was proposed.     

Tandem mass spectrometry of kahalalides: identification of two new cyclic depsipeptides, kahalalide R and S from Elysia grandifolia

Spectra obtained using electrospray ionization mass spectrometry (ESI-MS) of the mollusk Elysia grandifolia showed a cluster of molecular ion peaks centered at a molecular mass of 1478 Da (kahalalide F, an anticancer agent). Two new molecules, kahalalide R (m/z 1464) and S (m/z 1492) were characterized using tandem mass spectrometry. The mass differences of 14 Da suggest that they are homologous molecules. In addition, previously identified kahalalide D and kahalalide G are also reported. However, the ESI-MS of the mollusk's algal diet Bryopsis plumosa showed the presence of only kahalalide F. The amino acid sequences of kahalalide R and S are proposed using collision-induced dissociation (CID) experiments of singly and doubly charged molecular ions and by comparison with the amino acid sequence of kahalalide F. The pathway is presented for the loss of amino acid residues in kahalalide F. It is observed that there is sequential loss of amino acids in the linear peptide chain, but in the cyclic part the ring opens at the amide bond rather than at the lactone linkage, and the loss of amino acid residues is not sequential. The CID experiment of the alkali-metal-cationized molecular ions shows that the sodium and potassium ions coordinate to the amide nitrogen/oxygen in the linear peptide chain of the molecule and not to the lactone oxygen of the lactone. In the case of kahalalide D, CID of the protonated peptide opens the depsipeptide ring to form a linear peptide with acylium ion, and fragment ion signals indicate losses of amino acids in sequential order. In this study, tandem mass spectrometry has provided the detailed information required to fully characterize the new peptides.     

Characterization of a cross-linked DNA-Endonuclease VIII repair complex by electrospray ionization mass spectrometry

Electrospray mass spectrometry techniques were used to characterize components of the active site in Endonuclease VIII by identifying the amino acid sequence and the binding site for a tryptic peptide derived from Endo VIII in a cross-linked DNA-peptide complex. Endo VIII, a DNA repair enzyme with both glycosylase and lyase activities, was covalently bound to a thymidine glycol-containing oligodeoxynucleotide duplex by converting a transient Schiff base formed during the course of the glycosylase activity to a stable covalent bond by chemical reduction with sodium borohydride. After tryptic digestion of the initial product, the identification of the cross-linked peptide was deduced initially from the molecular mass of the tryptic product obtained by negative ion electrospray mass analysis. Nanospray tandem mass spectrometry (MS/MS) analysis of the tryptic product corroborated the molecular mass of the peptide fragment and verified the point of attachment to the oligomer, but failed to produce sufficient fragmentation to sequence the peptide completely. Direct evidence for the amino acid sequence of the peptide was obtained after enzymatic digestion of the DNA portion of the cross-linked DNA-peptide product and analysis by negative ion nanospray MS/MS. Examination of the ions from collision induced fragmentation disclosed that this substance was the N-terminal tryptic fragment of Endo VIII cross-linked to a portion of the oligomer, and that the N-terminal proline from Endo VIII was covalently bound to the residual deoxyribose moiety at the original location of the thymine glycol in the oligomer.     

Occurrence of C-Terminal Residue Exclusion in Peptide Fragmentation by ESI and MALDI Tandem Mass Spectrometry

By screening a data set of 392 synthetic peptides MS/MS spectra, we found that a known C-terminal rearrangement was unexpectedly frequently occurring from monoprotonated molecular ions in both ESI and MALDI tandem mass spectrometry upon low and high energy collision activated dissociations with QqTOF and TOF/TOF mass analyzer configuration, respectively. Any residue localized at the C-terminal carboxylic acid end, even a basic one, was lost, provided that a basic amino acid such arginine and to a lesser extent histidine and lysine was present in the sequence leading to a fragment ion, usually depicted as (b_n-1 + H₂O) ion, corresponding to a shortened non-scrambled peptide chain. Far from being an epiphenomenon, such a residue exclusion from the peptide chain C-terminal extremity gave a fragment ion that was the base peak of the MS/MS spectrum in certain cases. Within the frame of the mobile proton model, the ionizing proton being sequestered onto the basic amino acid side chain, it is known that the charge directed fragmentation mechanism involved the C-terminal carboxylic acid function forming an anhydride intermediate structure. The same mechanism was also demonstrated from cationized peptides. To confirm such assessment, we have prepared some of the peptides that displayed such C-terminal residue exclusion as a C-terminal backbone amide. As expected in this peptide amide series, the production of truncated chains was completely suppressed. Besides, multiply charged molecular ions of all peptides recorded in ESI mass spectrometry did not undergo such fragmentation validating that any mobile ionizing proton will prevent such a competitive C-terminal backbone rearrangement. Among all well-known nondirect sequence fragment ions issued from non specific loss of neutral molecules (mainly H₂O and NH₃) and multiple backbone amide ruptures (b-type internal ions), the described C-terminal residue exclusion is highly identifiable giving raise to a single fragment ion in the high mass range of the MS/MS spectra. The mass difference between this signal and the protonated molecular ion corresponds to the mass of the C-terminal residue. It allowed a straightforward identification of the amino acid positioned at this extremity. It must be emphasized that a neutral residue loss can be misattributed to the formation of a y_m-1 ion, i.e., to the loss of the N-terminal residue following the a₁-y_m–1 fragmentation channel. Extreme caution must be adopted when reading the direct sequence ion on the positive ion MS/MS spectra of singly charged peptides not to mix up the attribution of the N- and C-terminal amino acids. Although such peculiar fragmentation behavior is of obvious interest for de novo peptide sequencing, it can also be exploited in proteomics, especially for studies involving digestion protocols carried out with proteolytic enzymes other than trypsin (Lys-N, Glu-C, and Asp-N) that produce arginine-containing peptides.     

土壤中一种新的尿素衍生物的电喷雾萃取电离质谱分析

采用电喷雾萃取电离串联质谱(EESI-MSⁿ)技术直接分析马尾松根际土壤溶液, 发现了一种不稳定的尿素衍生物3,3-二氨基-3-羟基丙酸. 为确证其结构, 以尿素为原料合成了该衍生物, 并采用EESI-MSⁿ分析合成产物. 结果表明, 合成产物与土壤溶液中的3,3-二氨基-3-羟基丙酸的EESI-MSⁿ分析结果相吻合, 说明土壤中确实存在该衍生物, 其可能是一种尿素在土壤里代谢过程的中间体. 本文结果表明, EESI-MS技术可以直接分析复杂基体样品中痕量物质的信号, 为研究尿素在土壤中的氮素转化机理提供了新的思路.     

电喷雾质谱法研究氨基酸的质谱碎裂及其与人参皂苷Rb3的相互作用

用串联质谱法研究了18种常见氨基酸在正离子和负离子模式下的质谱碎裂规律. 结果表明, 在正离子模式下的分子离子峰强度比在负离子模式下的高一个数量级, 氨基酸α-C上的羧基和氨基容易脱掉. 在正离子和负离子模式下都有两种裂解机理. 用电喷雾软电离技术研究了人参皂苷Rb3与18种氨基酸的非共价相互作用, 并采用直接计算的方法得出这些非共价复合物的解离常数. 结果表明, 在水介质中,与其它氨基酸相比, 酸性氨基酸和碱性氨基酸与人参皂苷结合更稳定.     

Comparison of flow injection analysis electrospray mass spectrometry and tandem mass spectrometry and electrospray high-field asymmetric waveform ion mobility mass spectrometry and tandem mass spectrometry for the determination of underivatized amino acids

Twenty proteinogenic amino acids (AAs) were determined without derivatization using flow injection analysis followed by electrospray ionization mass spectrometry and tandem mass spectrometry (ESI-MS and ESI-MS/MS) and electrospray ionization high-field asymmetric waveform ion mobility mass spectrometry and tandem mass spectrometry (ESI-FAIMS-MS and ESI-FAIMS-MS/MS), in positive and negative ionization modes. Three separate sets of ESI-FAIMS conditions were used for the separation and detection of the 20 AAs. Typically ESI-FAIMS-MS showed somewhat improved sensitivity and significantly better signal-to-noise ratios than ESI-MS mainly due to the elimination of background noise. However, the difference between ESI-FAIMS-MS and ESI-MS/MS was significantly less. ESI-FAIMS was able to partially or completely resolve all the isobaric amino acid overlaps such as leucine, isoleucine and hydroxyproline or lysine and glutamine. Detection limits for the amino acids in ESI-FAIMS-MS mode ranged from 2 ng/mL for proline to 200 ng/mL for aspartic acid. Overall, ESI-FAIMS-MS is the preferred method for the quantitative analysis of AAs in a hydrolyzed yeast matrix.     

Mass spectrometric study of novel estra derivatives of amino acids and peptides

The mass spectra of novel estra derivatives of amino acids and peptides were studied using electron impact and fast atom bombardment ionization, high-resolution data and mass-analysed ion kinetic energy spectrometry. The characteristic peaks of the basic nucleus of estrogenic steroids, the amino acid sequence of the peptide chain and partial skeletal rearrangement of some of these compounds were observed.     

甾体磷酰胺类缀合物在电喷雾质谱中的裂解特征

Novel steroidal phosphoramidate conjugates of 3'-azido-2',3'-dideoxythymidine(AZT)and amino acid esterswere synthesized and determined by positive and negative ion electrospray ionization mass spectrometry.The MSfragmentation behaviors of the steroidal phosphoramidate conjugates have been investigated in conjunction withtandem mass spectrometry of ESI-MS/MS.There were three characteristic fragment ions in the positive ion ESImass spectra,which were the Na adduct ions with loss of steroidal moiety,amino acid ester moiety from pseudomolecular ion(M Na)~ ,and the phosphoamino acid methyl ester Na adduct ion by α-cleavage of the phosphora-midate respectively.The main fragment ions in negative ion ESI mass spectra were the ion(M-HN_3)~-,the ion(M-AZT-H)~-,and the ion(M-steroidal moiety-H)~- besides the pseudo molecular ion(M-H)~-.Thefragmentation patterns did not depend on the attached amino acid ester moiety.     

Electrospray Ionization Mass Spectra of Amino Acid Methyl Ester 5 ＇-Phosphoramidates of 2＇, 3＇-Isopropylideneuridine

Amino acid methyl ester phosphates were synthesized and determined by using positive-ion mode dectrospmy ionization mass spectrometry（ESIMS） in combination with multistage tandem mass spectrometry. The fragmentation pathways were investigated, and it was observed that most fragment ions contained the phosphoryl group. It was interesting to observe that the fragmentation pathways of the protonated molecule show some differences when compared with those of the sodium ion adduct. The methoxy group of amino acid methyl ester can migrate from the carbonyl group to the phosphoryl group in the sodium ion adduct.