Proteomics of total membranes and subcellular membranes

Membrane proteins are key molecules in the cell and are important targets for drug development. Much effort has, therefore, been directed towards research of this group of proteins, but their hydrophobic nature can make working with them challenging. Here we discuss methodologies used in the study of the membrane proteome, specifically discussing approaches that circumvent technical issues specific to the membrane. In addition, we review several techniques used for visualization, qualification, quantitation and localization of membrane proteins. The combination of the techniques we describe holds great promise to allow full characterization of the membrane proteome and to map the dynamic changes within it essential for cellular function.     

Application of Mass Spectrometry in Proteomics

Mass spectrometry has arguably become the core technology in proteomics. The application of mass spectrometry based techniques for the qualitative and quantitative analysis of global proteome samples derived from complex mixtures has had a big impact in the understanding of cellular function. Here, we give a brief introduction to principles of mass spectrometry and instrumentation currently used in proteomics experiments. In addition, recent developments in the application of mass spectrometry in proteomics are summarised. Strategies allowing high-throughput identification of proteins from highly complex mixtures include accurate mass measurement of peptides derived from total proteome digests and multidimensional peptide separations coupled with mass spectrometry. Mass spectrometric analysis of intact proteins permits the characterisation of protein isoforms. Recent developments in stable isotope labelling techniques and chemical tagging allow the mass spectrometry based differential display and quantitation of proteins, and newly established affinity procedures enable the targeted characterisation of post-translationally modified proteins. Finally, advances in mass spectrometric imaging allow the gathering of specific information on the local molecular composition, relative abundance and spatial distribution of peptides and proteins in thin tissue sections.     

Analysis of cytosolic and plastidic serine acetyltransferase mutants and subcellular metabolite distributions suggests interplay of the cellular compartments for cysteine biosynthesis in Arabidopsis

In plants, the enzymes for cysteine synthesis serine acetyltransferase (SAT) and O-acetylserine-(thiol)-lyase (OASTL) are present in the cytosol, plastids and mitochondria. However, it is still not clearly resolved to what extent the different compartments are involved in cysteine biosynthesis and how compartmentation influences the regulation of this biosynthetic pathway. To address these questions, we analysed Arabidopsis thaliana T-DNA insertion mutants for cytosolic and plastidic SAT isoforms. In addition, the subcellular distribution of enzyme activities and metabolite concentrations implicated in cysteine and glutathione biosynthesis were revealed by non-aqueous fractionation (NAF). We demonstrate that cytosolic SERAT1.1 and plastidic SERAT2.1 do not contribute to cysteine biosynthesis to a major extent, but may function to overcome transport limitations of O-acetylserine (OAS) from mitochondria. Substantiated by predominantly cytosolic cysteine pools, considerable amounts of sulphide and presence of OAS in the cytosol, our results suggest that the cytosol is the principal site for cysteine biosynthesis. Subcellular metabolite analysis further indicated efficient transport of cysteine, γ -glutamylcysteine and glutathione between the compartments. With respect to regulation of cysteine biosynthesis, estimation of subcellular OAS and sulphide concentrations established that OAS is limiting for cysteine biosynthesis and that SAT is mainly present bound in the cysteine–synthase complex.     

2DE-MS中膜蛋白质组的研究进展

2-维凝胶电泳(2DE)具有高分辨率、高通量等特点,已被广泛地用于蛋白质组的研究.然而,2DE-MS在膜蛋白质组学研究方面却有其局限性,主要因为:膜蛋白具有低丰度、难溶、等电点时易沉淀、难酶解等特点.然而随着亚细胞分离技术和直接的生化方法富集等技术的发展,低丰度问题得到了极大的改善;增溶剂(尿素,硫脲),新的两性离子和非离子去垢剂,以及有机溶剂等的利用极大地改善了膜蛋白质组的溶解性能;同时,一些新的2DE技术的利用扩大了常规2DE的分离范围.在膜蛋白裂解方面,将酶解法与化学法(CNBr)相结合,另外先进的质谱技术的发展使得膜蛋白质组的研究在最近几年取得了较大的发展.现对2DE-MS途径中,膜的富集、膜蛋白的提取、分离、酶解、鉴定方面的进展进行综述.     

Proteomics of chloroplast envelope membranes

Proteomics is a very powerful approach to link the information contained in sequenced genomes, like Arabidopsis, to the functional knowledge provided by studies of plant cell compartments, such as chloroplast envelope membranes. This review summarizes the present state of proteomic analyses of highly purified spinach and Arabidopsis envelope membranes. Methods targeted towards the hydrophobic core of the envelope allow identifying new proteins, and especially new transport systems. Common features were identified among the known and newly identified putative envelope inner membrane transporters and were used to mine the complete Arabidopsis genome to establish a virtual plastid envelope integral protein database. Arabidopsis envelope membrane proteins were extracted using different methods, that is, chloroform/methanol extraction, alkaline or saline treatments, in order to retrieve as many proteins as possible, from the most to the less hydrophobic ones. Mass spectrometry analyses lead to the identification of more than 100 proteins. More than 50% of the identified proteins have functions known or very likely to be associated with the chloroplast envelope. These proteins are (a) involved in ion and metabolite transport, (b) components of the protein import machinery and (c) involved in chloroplast lipid metabolism. Some soluble proteins, like proteases, proteins involved in carbon metabolism or in responses to oxidative stress, were associated with envelope membranes. Almost one third of the newly identified proteins have no known function. The present stage of the work demonstrates that a combination of different proteomics approaches together with bioinformatics and the use of different biological models indeed provide a better understanding of chloroplast envelope biochemical machinery at the molecular level.     

蛋白质组学研究相关技术及进展

蛋白质组学以蛋白质组为研究对象,应用相关研究技术,从整体水平上来认识蛋白的存在及活动方式。随着人类基因组计划的完成,蛋白质组学的研究也得到了快速发展,与蛋白质组学研究相关的一些技术也日益得到完善和提高。简要综述了近年来蛋白质组学研究中最为重要的样品制备、蛋白质分离、蛋白质鉴定等技术及研究进展。     

细胞质膜蛋白质组学研究技术进展

质膜蛋白在细胞中执行着非常重要的功能。随着蛋白质组学的发展,细胞质膜蛋白质组学成为蛋白质组学研究的重要组成部分,它为质膜蛋白的生物功能研究及药物靶标的发现提供了新的途径。然而,质膜蛋白丰度低、疏水性强,对现有蛋白质组学研究技术提出了挑战。简要综述了近年来质膜蛋白质组研究的相关技术进展,包括富集、提取分离鉴定方法及定量和生物信息学研究方法等。     

ABRF-PRG07: Advanced Quantitative Proteomics Study

A major challenge for core facilities is determining quantitative protein differences across complex biological samples. Although there are numerous techniques in the literature for relative and absolute protein quantification, the majority is nonroutine and can be challenging to carry out effectively. There are few studies comparing these technologies in terms of their reproducibility, accuracy, and precision, and no studies to date deal with performance across multiple laboratories with varied levels of expertise. Here, we describe an Association of Biomolecular Resource Facilities (ABRF) Proteomics Research Group (PRG) study based on samples composed of a complex protein mixture into which 12 known proteins were added at varying but defined ratios. All of the proteins were present at the same concentration in each of three tubes that were provided. The primary goal of this study was to allow each laboratory to evaluate its capabilities and approaches with regard to: detection and identification of proteins spiked into samples that also contain complex mixtures of background proteins and determination of relative quantities of the spiked proteins. The results returned by 43 participants were compiled by the PRG, which also collected information about the strategies used to assess overall performance and as an aid to development of optimized protocols for the methodologies used. The most accurate results were generally reported by the most experienced laboratories. Among laboratories that used the same technique, values that were closer to the expected ratio were obtained by more experienced groups.     

Light-dependent subcellular localization of nucleoside diphosphate kinase-1 in Neurospora crassa

Nucleoside diphosphate kinase (NDK) is a housekeeping enzyme localized in cellular organelles and distributed in various organs in prokaryotes and eukaryotes. In Neurospora crassa, NDK-1 is suggested to control catalases in response to heat, oxidative stress and light. In this study, we identified the presence of NDK-1 during most developmental stages in submerged mycelia, aerial hyphae, asexual conidia and perithecia, and the localization of it in soluble, mitochondrial, nuclear and membrane fractions in the mycelial cell. A light-dependent localization of NDK-1 was shown by Western blotting and immunohistochemical analysis using anti-NDK-1 antibody. In the mycelia, NDK-1 was compartmentalized on the plasma membrane in darkness, while it was relocated in the cytoplasm under light. These results suggest that NDK-1 protein was translocated from the plasma membrane to cytoplasm in response to light, and may interact with catalase.     

Proteomics of plasma membrane microdomains

Plasma membrane microdomains represent subcompartments of the plasma membrane characterized by a specific lipid and protein composition. The recognition of microdomains in nearly all the eukaryotic membranes has accredited them with specialized functions in health and disease. Several proteomic studies have recently addressed the specific composition of plasma membrane microdomains, and will be reviewed in this paper. Peculiar information has been obtained, but a comprehensive view of the main protein classes required to define the microdomain proteome is still missing. The achievement of this information is slowed by the difficulties encountered in resolving and analyzing hydrophobic proteins, but it could help in understanding the overall function of plasma membrane microdomains and their involvement in human pathology.     

酵母双杂交技术及其在蛋白质组研究中的应用

蛋白质组学是后基因组时代出现的一个新兴的研究领域,它的主要任务是识别鉴定细胞,组织或机体的全部蛋白质,并分析蛋白质的功能及其模式。因此,揭示蛋白质组中蛋白质间的相互作用关系也是蛋白质组学的重要内容之一。酵母双杂交技术是用来检测蛋白质间是否相互作用的一个非常有效的手段,该技术在酵母蛋白质组研究中的初步成功应用,表明它有望在人类蛋白质且研究中发挥重要作用。     

生物质谱技术与蛋白质组学

生物质谱技术是蛋白质组学的支撑技术.详细论述了质谱技术的分类与基本分析原理,重点论述了质谱技术的发展变化,包括基质辅助激光解吸飞行时间质谱技术,电喷雾质谱技术,MALDI-Q-TOF和MAL-DI-TOF-TOF等质谱技术,以及质谱技术在蛋白质组学研究中的应用与未来的发展和挑战.     

对脂肪滴的新认识

早在 1674 年, van Leeuwenhoeck 就首次在牛奶里发现了脂肪滴 . 从那以后, 300 多年过去了,有关脂肪滴的许多根本问题仍然没有得到解决 . 迄今,除有为数不多的几个脂肪滴表面蛋白被发现外,人类对脂肪滴的认识仍停留在其作为中性脂贮存器上 . 为了更好地认识脂肪滴,我们以及其他几个研究小组分别从不同细胞中纯化了脂肪滴,然后使用质谱蛋白分析对这些脂肪滴的蛋白质进行了蛋白质组学研究,从中发现了两组非常有意义的功能蛋白 . 一组是与脂肪合成及代谢有关的酶,另一组则是与膜转运有关的蛋白质 . 尽管这些实验使用了不同的细胞,而且是由不同实验室分别完成的,但结果却非常相似 . 这些发现表明,脂肪滴有可能是一种具有生理代谢活性的非常复杂的细胞器 . 同时,它有可能参与细胞内的脂肪合成、代谢及转运 . 这篇综述将重点介绍近年来的脂肪滴蛋白质组学研究进展,以及由此推测的脂肪滴的生理功能 . 如果读者希望了解脂肪滴的其他方面内容,请阅读 Denis Murphy 发表于 2001 年的一篇非常完整的综述 .     

蛋白质亚细胞定位预测中的序列编码技术

蛋白质序列的编码是亚细胞定位预测问题中的关键技术之一。该文较为详细地介绍了目前已有的蛋白质序列编码算法;并指出了序列编码中存在的一些问题及可能的发展方向。     

Interaction Proteomics

The term proteome is traditionally associated with the identification of a large number of proteins within complex mixtures originating from a given organelle, cell or even organism. Current proteome investigations are basically focused on two major areas, expression proteomics and functional proteomics. Both approaches rely on the fractionation of protein mixtures essentially by two-dimensional polyacrylamide gel electrophoresis (2D-gel) and the identification of individual protein bands by mass spectrometric techniques (2D-MS). Functional proteomics approaches are basically addressing two main targets, the elucidation of the biological function of unknown proteins and the definition of cellular mechanisms at the molecular level. In the cell many processes are governed not only by the relative abundance of proteins but also by rapid and transient regulation of activity, association and localization of proteins and protein complexes. The association of an unknown protein with partners belonging to a specific protein complex involved in a particular process would then be strongly suggestive of its biological function. The identification of interacting proteins in stable complexes in a cellular system is essentially achieved by affinity-based procedures. Different strategies relying on this simple concept have been developed and a brief overview of the main approaches presently used in functional proteomics studies is described.     

定量蛋白质组学分析PknG在分枝杆菌中的功能

丝氨酸苏氨酸蛋白激酶G(PknG)是分枝杆菌中一个类似于真核生物蛋白激酶C的蛋白质,对结核分枝杆菌的生长和新陈代谢等生理过程,以及结核分枝杆菌的耐药和在宿主细胞中的存活都起着重要的调节作用.本文在耻垢分枝杆菌(Mycobacterium smegmatis)mc2155中构建了过表达结核分枝杆菌PknG的重组菌株PknG-mc2155,并发现PknG-mc2155的生长速度慢于mc2155.应用化学修饰结合LC-LC-MS/MS的定量蛋白质组学方法,在mc2155和PknG-mc2155中鉴定到了176种有差异表达的蛋白,其中152种蛋白在PknG-mc2155中表达下调,24种蛋白表达上调.这些差异表达的蛋白参与了多个细胞过程,包括代谢、蛋白翻译等.基于这些结果,我们推测PknG-mc2155生长速度慢的原因是因为代谢相关酶如GlpK,ALD和DesA1等蛋白表达的下调;而Ag85A,Ag85C,SecA2等蛋白的上调则增强细菌的感染性;另外KatG蛋白的下调提示PknG的过表达增强了菌株的抗药性.代谢组学分析发现谷氨酸和谷氨酰胺在PknG-mc2155中的水平低于在mc2155中水平,证实了PknG影响谷氨酰胺的稳态平衡.利用蛋白质磷酸化分析,我们发现PknG的苏氨酸残基T-320上有一个自磷酸化修饰,而且在PknG-mc2155菌株中,也鉴定到gltA和glmM上的磷酸化修饰,显示gltA和glmM是PknG的底物.本研究为理解PknG的功能和作用机制提供了新的依据和解释,为深入研究PknG在结核分枝杆菌中的功能奠定了基础,我们的结果也表明蛋白质组学技术是系统研究细菌蛋白质功能的重要工具.     

MORN motifs in plant PIPKs are involved in the regulation of subcellular localization and phospholipid binding

Multiple repeats of membrane occupation and recognition nexus （MORN） motifs were detected in plant phosphatidylinositl monophosphate kinase （PIPK）, a key enzyme in PI-signaling pathway. Structural analysis indicates that all the MORN motifs （with varied numbers at ranges of 7-9）, which shared high homologies to those of animal ones, were located at N-terminus and sequentially arranged, except those of OsPIPK1 and AtPIPK7, in which the last MORN motif was separated others by an -100 amino-acid ＂island＂ region, revealing the presence of two kinds of MORN arrangements in plant PIPKs. Through employing a yeast-based SMET （sequence of membrane-targeting） system, the MORN motifs were shown being able to target the fusion proteins to cell plasma membrane, which were further confirmed by expression of fused MORN-GFP proteins. Further detailed analysis via deletion studies indicated the MORN motifs in OsPIPK 1, together with the 104 amino-acid ＂island＂ region are involved in the regulation of differential subcellular localization, i.e. plasma membrane or nucleus, of the fused proteins. Fat Western blot analysis of the recombinant MORN polypeptide, expressed in Escherichia coli, showed that MORN motifs could strongly bind to PA and relatively slightly to PI4P and PI（4,5）P2. These results provide informative hints on mechanisms of subcellular localization, as well as regulation of substrate binding, of plant PIPKs.