Integrating 'top-down" and "bottom-up" mass spectrometric approaches for proteomic analysis of Shewanella oneidensis

Here we present a comprehensive method for proteome analysis that integrates both intact protein measurement ("top-down") and proteolytic fragment characterization ("bottom-up") mass spectrometric approaches, capitalizing on the unique capabilities of each method. This integrated approach was applied in a preliminary proteomic analysis of Shewanella oneidensis, a metal-reducing microbe of potential importance to the field of bioremediation. Cellular lysates were examined directly by the "bottom-up" approach as well as fractionated via anion-exchange liquid chromatography for integrated studies. A portion of each fraction was proteolytically digested, with the resulting peptides characterized by on-line liquid chromatography/tandem mass spectrometry. The remaining portion of each fraction containing the intact proteins was examined by high-resolution Fourier transform mass spectrometry. This "top-down" technique provided direct measurement of the molecular masses for the intact proteins and thereby enabled confirmation of post-translational modifications, signal peptides, and gene start sites of proteins detected in the "bottom-up" experiments. A total of 868 proteins from virtually every functional class, including hypotheticals, were identified from this organism.     

Application of the accurate mass and time tag approach to the proteome analysis of sub-cellular fractions obtained from Rhodobacter sphaeroides 2.4.1. Aerobic and photosynthetic cell cultures

The high-throughput accurate mass and time (AMT) tag proteomic approach was utilized to characterize the proteomes for cytoplasm, cytoplasmic membrane, periplasm, and outer membrane fractions from aerobic and photosynthetic cultures of the gram-nagtive bacterium Rhodobacter sphaeroides 2.4.1. In addition, we analyzed the proteins within purified chromatophore fractions that house the photosynthetic apparatus from photosynthetically grown cells. In total, 8,300 peptides were identified with high confidence from at least one subcellular fraction from either cell culture. These peptides were derived from 1,514 genes or 35% percent of proteins predicted to be encoded by the genome. A significant number of these proteins were detected within a single subcellular fraction and their localization was compared to in silico predictions. However, the majority of proteins were observed in multiple subcellular fractions, and the most likely subcellular localization for these proteins was investigated using a Z-score analysis of estimated protein abundance along with clustering techniques. Good (81%) agreement was observed between the experimental results and in silico predictions. The AMT tag approach provides localization evidence for those proteins that have no predicted localization information, those annotated as putative proteins, and/or for those proteins annotated as hypothetical and conserved hypothetical.     

The genes encoding the two carboxyltransferase subunits of Escherichia coli acetyl-CoA carboxylase.

We report characterization of the component proteins and molecular cloning of the genes encoding the two subunits of the carboxyltransferase component of the Escherichia coli acetyl-CoA carboxylase. Peptide mapping of the purified enzyme component indicates that the carboxyltransferase component is a complex of two nonidentical subunits, a 35-kDa alpha subunit and a 33-kDa beta subunit. The alpha subunit gene encodes a protein of 319 residues and is located immediately downstream of the polC gene (min 4.3 of the E. coli genetic map). The deduced amino acid composition, molecular mass, and amino acid sequence match those determined for the purified alpha subunit. Six sequenced internal peptides also match the deduced sequence. The amino-terminal sequence of the beta subunit was found within a previously identified open reading frame of unknown function called dedB and usg (min 50 of the E. coli genetic map) which encodes a protein of 304 residues. Comparative peptide mapping also indicates that the dedB/usg gene encodes the beta subunit. Moreover, the deduced molecular mass and amino acid composition of the dedB/usg-encoded protein closely match those determined for the beta subunit. The deduced amino acid sequences of alpha and beta subunits show marked sequence similarities to the COOH-terminal half and the NH2-terminal halves, respectively, of the rat propionyl-CoA carboxylase, a biotin-dependent carboxylase that catalyzes a similar carboxyltransferase reaction reaction. Several conserved regions which may function as CoA-binding sites are noted.     

木质素生物合成酶CCR基因的生物信息学分析

肉桂酰辅酶A还原酶(Cinnamoyl-CoA reductase,CCR)是催化木质素特异途径的第一个关键酶,是调节碳素流向木质素潜在的控制关节点,对木质素单体的生物合成起着重要作用。通过NCBI数据库收集来自裸子植物、单子叶植物及双子叶植物的35条CCR基因的完整信息,对35条CCR基因的cDNA及其编码的氨基酸序列的进化规律、理化性质、结构域、导肽、信号肽、跨膜结构域、亲/疏水性以及蛋白质结构等性状进行了生物信息学分析与预测,构建了CCR基因的系统发育树。分析结果表明,单子叶植物CCR基因中GC的含量明显高于双子叶植物;CCR基因编码的氨基酸序列存在9个保守区域;所编码氨基酸的理化性质基本一致,但单子叶、双子叶及裸子植物的CCR基因编码主要氨基酸的种类和含量存在着差异;CCR蛋白的N-端存在一个脱氢酶/差向异构酶/辅酶Ⅰ结合蛋白的结构域,无导肽、信号肽及跨膜结构域,属亲水性蛋白;进化树绘制以及同源建模结果表明,CCR基因的进化和植物的进化基本一致,CCR蛋白三级结构模型的空间结构稳定,建模结果可靠。分析结果对于深入研究CCR蛋白在木质素合成中的作用具有一定的理论指导意义。     

Determination and comparison of the baseline proteomes of the versatile microbe Rhodopseudomonas palustris under its major metabolic states

Rhodopseudomonas palustris is a purple nonsulfur anoxygenic phototrophic bacterium that is ubiquitous in soil and water. R. palustris is metabolically versatile with respect to energy generation and carbon and nitrogen metabolism. We have characterized and compared the baseline proteome of a R. palustris wild-type strain grown under six metabolic conditions. The methodology for proteome analysis involved protein fractionation by centrifugation, subsequent digestion with trypsin, and analysis of peptides by liquid chromatography coupled with tandem mass spectrometry. Using these methods, we identified 1664 proteins out of 4836 predicted proteins with conservative filtering constraints. A total of 107 novel hypothetical proteins and 218 conserved hypothetical proteins were detected. Qualitative analyses revealed over 311 proteins exhibiting marked differences between conditions, many of these being hypothetical or conserved hypothetical proteins showing strong correlations with different metabolic modes. For example, five proteins encoded by genes from a novel operon appeared only after anaerobic growth with no evidence of these proteins in extracts of aerobically grown cells. Proteins known to be associated with specialized growth states such as nitrogen fixation, photoautotrophic, or growth on benzoate, were observed to be up-regulated under those states.     

Initial proteome analysis of model microorganism Haemophilus influenzae strain Rd KW20

The proteome of Haemophilus influenzae strain Rd KW20 was analyzed by liquid chromatography (LC) coupled with ion trap tandem mass spectrometry (MS/MS). This approach does not require a gel electrophoresis step and provides a rapidly developed snapshot of the proteome. In order to gain insight into the central metabolism of H. influenzae, cells were grown microaerobically and anaerobically in a rich medium and soluble and membrane proteins of strain Rd KW20 were proteolyzed with trypsin and directly examined by LC-MS/MS. Several different experimental and computational approaches were utilized to optimize the proteome coverage and to ensure statistically valid protein identification. Approximately 25% of all predicted proteins (open reading frames) of H. influenzae strain Rd KW20 were identified with high confidence, as their component peptides were unambiguously assigned to tandem mass spectra. Approximately 80% of the predicted ribosomal proteins were identified with high confidence, compared to the 33% of the predicted ribosomal proteins detected by previous two-dimensional gel electrophoresis studies. The results obtained in this study are generally consistent with those obtained from computational genome analysis, two-dimensional gel electrophoresis, and whole-genome transposon mutagenesis studies. At least 15 genes originally annotated as conserved hypothetical were found to encode expressed proteins. Two more proteins, previously annotated as predicted coding regions, were detected with high confidence; these proteins also have close homologs in related bacteria. The direct proteomics approach to studying protein expression in vivo reported here is a powerful method that is applicable to proteome analysis of any (micro)organism.     

Mapping precursor-binding site on TatC subunit of twin arginine-specific protein translocase by site-specific photo cross-linking

A number of secreted precursor proteins of bacteria, archaea, and plant chloroplasts stand out by a conserved twin arginine-containing sequence motif in their signal peptides. Many of these precursor proteins are secreted in a completely folded conformation by specific twin arginine translocation (Tat) machineries. Tat machineries are high molecular mass complexes consisting of two types of membrane proteins, a hexahelical TatC protein, and usually one or two single-spanning membrane proteins, called TatA and TatB. TatC has previously been shown to be involved in the recognition of twin arginine signal peptides. We have performed an extensive site-specific cross-linking analysis of the Escherichia coli TatC protein under resting and translocating conditions. This strategy allowed us to map the recognition site for twin arginine signal peptides to the cytosolic N-terminal region and first cytosolic loop of TatC. In addition, discrete contact sites between TatC, TatB, and TatA were revealed. We discuss a tentative model of how a twin arginine signal sequence might be accommodated in the Tat translocase.     

Methionine sulfoxidation of the chloroplast small heat shock protein and conformational changes in the oligomer

The small heat shock proteins (sHsps), which counteract heat and oxidative stress in an unknown way, belong to a protein family of sHsps and alpha-crystallins whose members form large oligomeric complexes. The chloroplast-localized sHsp, Hsp21, contains a conserved methionine-rich sequence, predicted to form an amphipatic helix with the methionines situated along one of its sides. Here, we report how methionine sulfoxidation was detected by mass spectrometry in proteolytically cleaved peptides that were produced from recombinant Arabidopsis thaliana Hsp21, which had been treated with varying concentrations of hydrogen peroxide. Sulfoxidation of the methionine residues in the conserved amphipatic helix coincided with a significant conformational change in the Hsp21 protein oligomer.     

The distribution of alpha-helix propensity along the polypeptide chain is not conserved in proteins from the same family.

We address the question of whether the distribution of secondary structure propensities of the residues along the polypeptide chain (denominated here as secondary structure profiles) is conserved in proteins throughout evolution, for the particular case of alpha-helices. We have analyzed by CD the conformation of peptides corresponding to the five alpha-helices of two alpha/beta parallel proteins (ComA and Ara). The large alpha-helical population of peptide ComA-4 detected by CD in aqueous solution has been confirmed by NMR. These proteins are members of the CheY and P21-ras families, respectively, which have been studied previously in the same way (Muñoz V, Jiménez MA, Rico M, Serrano L, 1995, J Mol Biol 245:275-296). Comparison of the helical content of equivalent peptides reveals that protein alpha-helix propensity profiles are not conserved. Some equivalent peptides show very different helical populations in solution and this is especially evident in very divergent proteins (ComA and CheY). However, all the peptides analyzed so far adopted an important population of helical conformations in the presence of 30% trifluoroethanol, indicating that there could be a conserved minimal requirement for helical propensity.     

Internal proteins of bacteriophage T4D: Their characterization and relation to head structure and assembly

Three basic proteins of low molecular weight (about 8000, 10,000 and 18,000) were isolated from the T4D phage particle. Many molecules of each protein are located within the phage head, possibly in association with the DNA, and together with the proteins which form the head membrane comprise most of the head structural protein. The purified internal proteins were characterized by physicochemical and immunological techniques; a radio-immunoassay allowed measurement of their synthesis in phage infected bacteria. Each internal protein is synthesized at both early and late times after infection. Their structural genes are present in the phage genome, but do not appear to be among the known amber mutant-containing genes of T4D. No evidence was found to suggest that the internal proteins are formed from a common precursor molecule, nor are their origins related to those of the internal peptides; however, one of the internal proteins may be altered before its incorporation into the phage. Pulse-chase experiments with two of these proteins show that they are incorporated into certain defective T4D heads. Whether or not they are incorporated appears to depend on the degree of completion of these heads, perhaps with respect to DNA packaging.     

A novel functional class I lineage in zebrafish (Danio rerio), carp (Cyprinus carpio), and large barbus (Barbus intermedius) showing an unusual conservation of the peptide binding domains

Species from all major jawed vertebrate taxa possess linked polymorphic class I and II genes located in an MHC. The bony fish are exceptional with class I and II genes located on different linkage groups. Zebrafish (Danio rerio), common carp (Cyprinus carpio), and barbus (Barbus intermedius) represent highly divergent cyprinid genera. The genera Danio and Cyprinus diverged 50 million years ago, while Cyprinus and Barbus separated 30 million years ago. In this study, we report the first complete protein-coding class I ZE lineage cDNA sequences with high similarity between the three cyprinid species. Two unique complete protein-coding cDNA sequences were isolated in zebrafish, Dare-ZE*0101 and Dare-ZE*0102, one in common carp, Cyca-ZE*0101, and six in barbus, Bain-ZE*0101, Bain-ZE*0102, Bain-ZE*0201, Bain-ZE*0301, Bain-ZE*0401, and Bain-ZE*0402. Deduced amino acid sequences indicate that these sequences encode bonafide class I proteins. In addition, the presence of conserved potential peptide anchoring residues, exon-intron organization, ubiquitous expression, and polymorphism generated by positive selection on putative peptide binding residues support a classical nature of class I ZE lineage genes. Phylogenetic analyses revealed clustering of the ZE lineage clade with nonclassical cyprinid class I Z lineage clade away from classical cyprinid class I genes, suggesting a common ancestor of these nonclassical genes as observed for mammalian class I genes. Data strongly support the classical nature of these ZE lineage genes that evolved in a trans-species fashion with lineages being maintained for up to 100 million years as estimated by divergence time calculations.     

Structure of the human ubiquitin fusion gene Uba80 (RPS27a) and one of its pseudogenes

Ubiquitin is a highly conserved 76 amino acid protein that is generated in the cell by proteolysis of larger proteins containing either polyubiquitin chains or ubiquitin fused to carboxyl extension proteins (CEPs). In humans, the two human ubiquitin-CEP genes are Uba80 and Uba52, which code for ubiquitin fused to ribosomal protein S27a and L40, respectively. Working from a recently generated physical map of human chromosome 2p16, we determined the genetic and physical location and the genomic structure of the Uba80 gene in its entirety. A comparison of Uba80 to Uba52 revealed that the two genes share a conserved 5'-end structure, but that the structure of the ubiquitin coding regions was not conserved. Analysis of 400 bp of the promoter of Uba80 revealed strong similarity not only to the Uba52 promoter, but also to the other known human ribosomal gene promoters that have been identified to date. Homology searches also detected the presence of a pseudogene for Uba80, and the structure of this sequence feature is also reported.     

Large-scale identification of proteins in human salivary proteome by liquid chromatography/mass spectrometry and two-dimensional gel electrophoresis-mass spectrometry

Human saliva contains a large number of proteins and peptides (salivary proteome) that help maintain homeostasis in the oral cavity. Global analysis of human salivary proteome is important for understanding oral health and disease pathogenesis. In this study, large-scale identification of salivary proteins was demonstrated by using shotgun proteomics and two-dimensinal gel electrophoresis-mass spectrometry (2-DE-MS). For the shotgun approach, whole saliva proteins were prefractionated according to molecular weight. The smallest fraction, presumably containing salivary peptides, was directly separated by capillary liquid chromatography (LC). However, the large protein fractions were digested into peptides for subsequent LC separation. Separated peptides were analyzed by on-line electrospray tandem mass spectrometry (MS/MS) using a quadrupole-time of flight mass spectrometer, and the obtained spectra were automatically processed to search human protein sequence database for protein identification. Additionally, 2-DE was used to map out the proteins in whole saliva. Protein spots 105 in number were excised and in-gel digested; and the resulting peptide fragments were measured by matrix-assisted laser desorption/ionization-mass spectrometry and sequenced by LC-MS/MS for protein identification. In total, we cataloged 309 proteins from human whole saliva by using these two proteomic approaches.     

Improved strategies for rapid identification of chemically cross-linked peptides using protein interaction reporter technology

Protein interaction reporter (PIR) technology can enable identification of in vivo protein interactions with the use of specialized chemical cross-linkers, liquid chromatography, and high-resolution mass spectrometry. PIR-cross-linkers contain labile bonds that are specifically fragmented under low energy collision or photodissociation conditions in the mass spectrometer source, thus releasing cross-linked peptides. Successful analysis of PIR-cross-linked proteins requires the use of expected mathematical relationships between cross-linked complexes and released peptides after fragmentation of the labile PIR bonds. Presented here is a next-generation software tool, BLinks, for use in the analysis and identification of PIR-cross-linked proteins. BLinks is an advancement beyond our previous efforts by incorporation of chromatographic profiles that must match between cross-linked complexes and released peptides to enable estimation of p-values to help filter true relationships from complex data sets. Additionally, BLinks was used to incorporate Mascot database searching results from subsequent MS/MS analysis of the released peptides to facilitate identification of cross-linked proteins. BLinks was used in the analysis of human serum albumin, and 46 interpeptide relationships were found spanning 30 proximal residues with a 2.2% false discovery rate. BLinks was also used to track peptides involved in multiple, coeluting relationships that make accurate identification of protein interactions difficult. An additional 10 interpeptide relationships were identified despite poor correlation using the profiling tools provided with BLinks. Additionally, BLinks can be used to globally map all interpeptide relationships from the data analysis and customize subsequent analysis to target specific peptides of interest, thus making it a useful tool for both discovery of protein interactions and mapping protein topology.     

Evaluation of three different protocols of protein extraction for Arabidopsis thaliana leaf proteome analysis by two-dimensional electrophoresis

This work was performed to compare three precipitation protocols of protein extraction for 2-DE proteomic analysis using Arabidopsis leaf tissue: TCA-acetone, phenol, and TCA-acetone-phenol. There were no statistically significant differences in protein yield between the three methods. Samples were subjected to 2-DE in the 5 to 8 pH and 14-80 kDa ranges. The TCA-acetone-phenol protocol provided the best results in terms of spot focusing, resolved spots, spot intensity, unique spots detected, and reproducibility. In all, 93 qualitative or quantitative statistically significant differential spots were found between the three protocols. The 2-DE map of TCA-acetone-phenol extracts presented more resolved spots above 40 kDa, with no pI-dependent differences observed between the three protocols. 54 spots were selected for trypsin digestion, and the peptides were analyzed by MALDI-TOF-TOF MS. After database search using peptide mass fingerprinting, and MS/MS combined search, 30 proteins were identified, the proteins from chloroplastic photosynthetic and carbohydrate metabolism being those most highly represented. From these data, we were able to conclude that each extraction protocol had its main features. Considering this, the workflow of any standard comparative proteomic experiment should include the optimization and adaptation of the protein extraction protocol to the plant tissue and to the particular objective pursued.     

Computer analysis identifies sequence homologies between potential gene products of Maize Streak Virus and those of Cassava Latent Virus and Tomato Golden Mosaic Virus

Summary The amino acid sequences of the putative polypeptides of maize streak virus (MSV) have been systematically compared with those of cassava latent virus (CLV) and tomato golden mosaic virus (TGMV) using the programme DIAGON (8).Conserved sequences have been detected between peptides encoded by the complementary (-) sense of MSV and those of CLV and TGMV, viz; the 40 200 M_r polypeptide of CLV-1 (3) and the 40 285 M_r polypeptide of TGMV-A (4) show extensive homologies with the 17 768 M_r and 31 388 M_r polypeptides of MSV (6).Distant and variable homologies have been detected between the putative coat protein of MSV when compared with those of CLV and TGMV. No other relationships between the potential gene products of MSV and those of CLV and TGMV have been detected.The extensive homologies detected between the complementary sense encoded peptides suggest that they are derived from functional genes, and that the directly conserved sequences may contain amino acids essential to the function of these proteins. The less extensive homologies among the putative coat proteins are considered in relation to their possible structures and functions.     

A plant serpin gene. Structure, organization and expression of the gene encoding barley protein Z4

A 3133-bp nucleotide sequence of the gene Paz1 on chromosome 4 of barley, encoding endosperm protein Z4, has been determined. The sequence includes 1079 bp 5' upstream and 523 bp 3' downstream of the coding region. The 1079-bp 5' upstream region of the gene shows little similarity to 5' regions of other sequences genes expressed in the developing cereal endosperm. The coding sequence is interrupted by one 334-bp-long intron (bases 1497-1830). The deduced amino acid sequence, which was corroborated by peptide sequences, consists of 399 amino acids and has a molecular mass of 43,128 Da. This sequence confirms protein Z4 to be a member of the serpin superfamily of proteins. The similarity with other members of the family expressed as amino acids in identical positions is in the order of 25-30% and pronounced in the carboxy-terminal half of the molecule. Sequence residues assumed to form clusters stabilizing the tertiary structure are highly conserved. Protein Z4 is synthesized in the developing endosperm without a signal peptide and protein Z4 mRNA was evenly distributed among the free and membrane-bound polyribosomes of the endosperm cell. An internal hydrophobic region of 21 amino acids (residues 36-56) may serve as a signal for targeting the polypeptide into the lumen of the endoplasmic reticulum. The gene for protein Z4 could not be detected in the barley variety Maskin and some of its descendants. The 'high-lysine' allees, lys1 (Hiproly barley) and lys3a (Bomi mutant 1508) on chromosome 7, enhance and repress, respectively, the expression of the protein Z4 gene. Also, 1554 bp of another 8-kbp fragment of the barley genome Paz psi, similar to the protein-Z4-coding region, have been determined. Small insertions and deletions and the presence of an internal stop codon identify this fragment as part of a pseudogene related to the protein Z4 gene.     

Comparison of the leader sequences of four group A streptococcal M protein genes.

The 5' portions and flanking sequences of genes encoding types 1, 12, 24, and 6 M proteins were compared. Although the DNA sequences encoding the amino-termini of the mature M proteins had no obvious similarity, upstream sequences, and those encoding the signal peptides (leader sequences) of the four M protein genes had considerable similarity. In general, the 5' ends of all the leader sequences were more conserved than the 3' ends, although the M6 and M24 leader sequences had identical 3' ends. Sequence similarity among the deduced amino acid sequences of the four signal peptides was more extensive than the corresponding DNA sequences. We found that strict DNA similarity among all four sequences extended only to the ends of the hydrophilic amino-terminal regions of the signal peptides, but that amino acid sequence conservation continued to the ends of the respective hydrophobic cores. With the exception of the M6 and M24 sequences, the regions adjacent to the signal peptidase cleavage sites were highly variable.