Trends in Codon and Amino Acid Usage in Thermotoga maritima

The usage of synonymous codons and the frequencies of amino acids were investigated in the complete genome of the bacterium Thermotoga maritima using a multivariate statistical approach. The GC3 content of each gene was the most prominent source of variation of codon usage. Surprisingly the usage of UGU and UGC (synonymous triplets coding for Cys, the least frequent amino acid in this species) was detected as the second most prominent source of variation. However, this result is probably an artifact due to the very low frequency of Cys together with the nonbiased composition of this genome. The third trend was related to the preferential usage of a subset of codons among highly expressed genes, and these triplets are presumed to be translationally optimal. Concerning the amino acid usage, the hydropathy level of each protein (and therefore the frequency of charged residues) was the main trend, while the second factor was related to the frequency of usage of the smaller residues, suggesting that the cell economy strongly influences the architecture of the proteins. The third axis of the analysis discriminated the usage of Phe, Tyr, Trp (aromatic residues) plus Cys, Met, and His. These six residues have in common the property of being the preferential targets of reactive oxygen species, and therefore the anaerobic condition of T. maritima is an important factor for the amino acid frequencies. Finally, the Cys content of each protein was the fourth trend. Received: 22 June 2001 / Accepted: 1 October 2001     

An Empirical Codon Model for Protein Sequence Evolution

Mol. Biol. Evol. 2007 24:1464-1479 The first affiliation should have appeared as EMBL-EuropeanBioinformatics Institute, Hinxton, United Kingdom. On page     

Amino Acid Biosynthetic Cost and Protein Conservation

Protein products of highly expressed genes tend to favor amino acids that have lower average biosynthetic costs (i.e., they exhibit metabolic efficiency). While this trend has been observed in several studies, the specific sites where cost-reducing substitutions accumulate have not been well characterized. Toward that end, weighted costs in conserved and variable positions were evaluated across a total of 9,119 homologous proteins in four mammalian orders (primate, carnivore, rodent, and artiodactyls), which together contain a total of 20,457,072 amino acids. Degree of conservation at homologous positions in these mammalian proteins and average-weighted cost across all positions within a single protein are significantly correlated. Dividing human genes into two classes (those with and those without CpG islands in their promoters) suggests that humans also preferentially utilize less costly amino acids in highly expressed genes. In contrast to the intuitive expectation that the relatively weak selective force associated with metabolic efficiency would be a selection pressure in complex multicellular organisms, the overall level of selective constraint within the variable regions of mammalian proteins allows the metabolic efficiency to derive a reduction of overall biosynthetic cost, particularly in genes with the highest levels of expression.     

氨基酸的置换与生物大分子进化的保守性的评析

以蛋白质分子的核氨基酸或核酸分子的核苷酸置换 ,阐明功能上重要的大分子在进化速率上低于那些功能上不重要的大分子———即生物大分子进化的保守性     

Evolution of Genetic Alphabet and of Amino Acid Code

On considering chemical evolution of the Earth since the time of its appearance when its composition was similar to the elementary composition of star substance, a tentative hypothesis has been put forward that molecular evolution of the four-letter genetic alphabet includes two periods: I (pre-oxygen) and II (oxygenated) periods of chemical evolution. At the period I, in the primary Earth atmosphere the first nitrogen base, adenine (A), containing no oxygen appeared. The period II, during which three other nitrogen bases appeared in the atmosphere, consisted of three stages; at the first stage, guanine (G) appeared, at the second, cytosine (C), and at the third stage, uracyl (U). In accordance with the above periods, formation of codons and amino acids in nature was taking place presumably by the following way: at the period I, the first and the only codon AAA appeared, to which the amino acid lysine (Lys) corresponded; at the first stage of the period II, 7 codons and 3 amino acids (Arg, Glu, Gly) appeared; at the second stage, 19 codons and 8 new amino acids (Asn, Gin, Ser, Asp, Thr, Ala, His, Pro) appeared; at the third stage, 37 codons and more 8 new amino acids (Trp, Tyr, Cys, Ile, Met, Val, Leu, Phe) appeared. Thereby, in the course of biochemical evolution, 20 amino acids and 64 codons appeared in nature.     

Evolution of Amino Acid Propensities under Stability-Mediated Epistasis

Site-specific amino acid preferences are influenced by the genetic background of the protein. The preferences for resident amino acids are expected to, on average, increase over time because of replacements at other sites—a nonadaptive phenomenon referred to as the “evolutionary Stokes shift.” Alternatively, decreases in resident amino acid propensity have recently been viewed as evidence of adaptations to external environmental changes. Using population genetics theory and thermodynamic stability constraints, we show that nonadaptive evolution can lead to both positive and negative shifts in propensities following the fixation of an amino acid, emphasizing that the detection of negative shifts is not conclusive evidence of adaptation. By examining propensity shifts from when an amino acid is first accepted at a site until it is subsequently replaced, we find that ≈50% of sites show a decrease in the propensity for the newly resident amino acid while the remaining sites show an increase. Furthermore, the distributions of the magnitudes of positive and negative shifts were comparable. Preferences were often conserved via a significant negative autocorrelation in propensity changes—increases in propensities often followed by decreases, and vice versa. Lastly, we explore the underlying mechanisms that lead propensities to fluctuate. We observe that stabilizing replacements increase the mutational tolerance at a site and in doing so decrease the propensity for the resident amino acid. In contrast, destabilizing substitutions result in more rugged fitness landscapes that tend to favor the resident amino acid. In summary, our results characterize propensity trajectories under nonadaptive stability-constrained evolution against which evidence of adaptations should be calibrated.     

Real-time Measurements of Amino Acid and Protein Hydroperoxides Using Coumarin Boronic Acid

Hydroperoxides of amino acid and amino acid residues (tyrosine, cysteine, tryptophan, and histidine) in proteins are formed during oxidative modification induced by reactive oxygen species. Amino acid hydroperoxides are unstable intermediates that can further propagate oxidative damage in proteins. The existing assays (oxidation of ferrous cation and iodometric assays) cannot be used in real-time measurements. In this study, we show that the profluorescent coumarin boronic acid (CBA) probe reacts with amino acid and protein hydroperoxides to form the corresponding fluorescent product, 7-hydroxycoumarin. 7-Hydroxycoumarin formation was catalase-independent. Based on this observation, we have developed a fluorometric, real-time assay that is adapted to a multiwell plate format. This is the first report showing real-time monitoring of amino acid and protein hydroperoxides using the CBA-based assay. This approach was used to detect protein hydroperoxides in cell lysates obtained from macrophages exposed to visible light and photosensitizer (rose bengal). We also measured the rate constants for the reaction between amino acid hydroperoxides (tyrosyl, tryptophan, and histidine hydroperoxides) and CBA, and these values (7–23 m⁻¹ s⁻¹) were significantly higher than that measured for H₂O₂ (1.5 m⁻¹ s⁻¹). Using the CBA-based competition kinetics approach, the rate constants for amino acid hydroperoxides with ebselen, a glutathione peroxidase mimic, were also determined, and the values were within the range of 1.1–1.5 × 10³ m⁻¹ s⁻¹. Both ebselen and boronates may be used as small molecule scavengers of amino acid and protein hydroperoxides. Here we also show formation of tryptophan hydroperoxide from tryptophan exposed to co-generated fluxes of nitric oxide and superoxide. This observation reveals a new mechanism for amino acid and protein hydroperoxide formation in biological systems.     

SuccSite: Incorporating Amino Acid Composition and Informative k-spaced Amino Acid Pairs to Identify Protein Succinylation Sites

Protein succinylation is a biochemical reaction in which a succinyl group (-CO-CH2-CH2-CO-) is attached to the lysine residue of a protein molecule. Lysine succinylation plays important regulatory roles in living cells. However, studies in this field are limited by the difficulty in experimentally identifying the substrate site specificity of lysine succinylation. To facilitate this process, several tools have been proposed for the computational identification of succinylated lysine sites. In this study, we developed an approach to investigate the substrate specificity of lysine succinylated sites based on amino acid composition. Using experimentally verified lysine succinylated sites collected from public resources, the significant differences in position-specific amino acid composition between succinylated and non-succinylated sites were represented using the Two Sample Logo program. These findings enabled the adoption of an effective machine learning method, support vector machine, to train a predictive model with not only the amino acid composition, but also the composition of k-spaced amino acid pairs. After the selection of the best model using a ten-fold cross-validation approach, the selected model significantly outperformed existing tools based on an independent dataset manually extracted from published research articles. Finally, the selected model was used to develop a web-based tool, SuccSite, to aid the study of protein succinylation. Two proteins were used as case studies on the website to demonstrate the effective prediction of succinylation sites. We will regularly update SuccSite by integrating more experimental datasets. SuccSite is freely accessible at http://csb.cse.yzu.edu.tw/SuccSite/.     

从氨基酸序列预测蛋白质折叠速率

蛋白质折叠速率预测是当今生物物理学最具挑战性的课题之一．近年来,许多科研工作者开展了大量的研究工作来探索折叠速率的决定因素,许多参数和方法被相继提出．但氨基酸残基间的相互作用、氨基酸的序列顺序等信息对折叠速率的影响从未被提及．采用伪氨基酸组成的方法提取氨基酸的序列顺序信息,利用蒙特卡洛方法选择最佳特征因子,建立线性回归模型进行折叠速率预测．该方法能在不需要任何(显示)结构信息的情况下,直接从蛋白质的氨基酸序列出发对折叠速率进行预测．在Jackknife交互检验方法的验证下,对含有99个蛋白质的数据集,发现折叠速率的预测值与实验值有很好的相关性,相关系数能达到0.81,预测误差仅为2.54．这一精度明显优于其他基于序列的方法,充分说明蛋白质的序列顺序信息是影响蛋白质折叠速率的重要因素．     

Human Protein Cluster Analysis Using Amino Acid Frequencies

The paper focuses on the development of a software tool for protein clustering according to their amino acid content. All known human proteins were clustered according to the relative frequencies of their amino acids starting from the UniProtKB/Swiss-Prot reference database and making use of hierarchical cluster analysis. Results were compared to those based on sequence similarities. Results: Proteins display different clustering patterns according to type. Many extracellular proteins with highly specific and repetitive sequences (keratins, collagens etc.) cluster clearly confirming the accuracy of the clustering method. In our case clustering by sequence and amino acid content overlaps. Proteins with a more complex structure with multiple domains (catalytic, extracellular, transmembrane etc.), even if classified very similar according to sequence similarity and function (aquaporins, cadherins, steroid 5-alpha reductase etc.) showed different clustering according to amino acid content. Availability of essential amino acids according to local conditions (starvation, low or high oxygen, cell cycle phase etc.) may be a limiting factor in protein synthesis, whatever the mRNA level. This type of protein clustering may therefore prove a valuable tool in identifying so far unknown metabolic connections and constraints.     

氨基酸组成对蛋白质耐热性的影响

为了研究一级结构对蛋白质耐热性的影响,利用软件DNAMAN对16个家族32种蛋白质序列进行了氨基酸含量分析,并统计分析了氨基酸组成对蛋白质耐热性的影响。通过比较同一家族的高低温蛋白质序列及16个家族中所有高温和低温蛋白质序列中氨基酸含量的变化可以推断(从低温到高温)：Ser、Cys．含量降低显著,Arg、Ile、Pro含量升高显著。由此可知高温蛋白质倾向于含有疏水性氨基酸而避免亲水性氨基酸。     

Amino Acid Sequence of Porcine Myelin Basic Protein

The myelin basic protein (BP) of pig brain was cleaved into its constituent tryptic peptides and the amino acid composition of each was determined. Those tryptic peptides that had not been sequenced previously were cleaved with dipeptidyl peptidases and the resulting dipeptides were trimethylsilated, separated by gas chromatography, and identified by mass spectrometry. Carboxypeptidases B and Y were used to establish the COOH-terminal sequences of some of the tryptic peptides; one tryptic peptide (sequence 76-92) was cleaved with thermolysin and the thermolytic peptides were analyzed. From the results of the present study together with those reported previously, it has been possible to determine the complete amino acid sequence of the protein. The protein consists of 172 residues and has a theoretical molecular weight of 18,604. Its amino acid sequence is identical with that reported for the homologous bovine protein with the following exceptions: Ser replaces (bovine) Ala2; His-Gly is inserted between Arg9 and Ser10; Ala replaces Ser45; His and Gly replace Gly76 and His77, respectively; Pro replaces Ser131 and Ser135; Ala is inserted between Gly142 and His143; and Gln replaces His143.     

氨基酸在蛋白质空间结构中的深度倾向性因子

用统计和几何方法给出了氨基酸在蛋白质空间结构中的深度计算,并利用PDB数据库得到了不同氨基酸在蛋白质中的深度倾向性因子,并得到了这些倾向性因子与氨基酸的物理、化学综合特性的相关性质.     

Polymorphism Due to Multiple Amino Acid Substitutions at a Codon Site Within Ciona savignyi

We compared two haploid genotypes of one Ciona savignyi individual and identified codons at which these genotypes differ by two nonsynonymous substitutions. Using the C. intestinalis genome as an outgroup, we showed that both substitutions tend to occur in the same genotype. Only in 53 (34.4%) of 154 codons, one substitution occurred in each of the two genotypes, although 77 (50%) of such codons are to be expected if substitutions were independent. We considered two feasible evolutionary causes for the observed pattern: substitutions driven by positive selection and compensatory substitutions, as well as several potential biases. However, none of these explanations is fully compelling, and data on multiple genotypes of C. savignyi would help to elucidate the causes of this pattern.     

Antiviral Nucleoside Drug Delivery via Amino Acid Phosphoramidates

Abstract

Stable and water soluble amino acid phosphomonoester amidates of AZT were synthesized and shown to have potent anti-HIV-1 activity. Intracellular and cell extract metabolism studies revealed that these compounds are likely to be enzymatically converted to the corresponding monophosphates. In addition, we have shown that the half life and tissue distribution of a phosphoramidate of AZT is 5 and 10-fold greater, respectively, than AZT.     

Comparative Analysis of SOX3 Protein Orthologs: Expansion of Homopolymeric Amino Acid Tracts During Vertebrate Evolution

To understand more fully the structure and evolution of the SOX3 protein, we comparatively analyzed its orthologs in vertebrates. Since complex disorders are associated with human SOX3 polyalanine expansions, our investigation focused on both compositional and evolutionary analysis of various homopolymeric amino acid tracts observed in SOX3 orthologs. Our analysis revealed that the observed homopolymeric alanine, glycine, and proline tracts are mammal-specific, except for one polyglycine tract present in birds. Since it is likely that the SOX3 protein acquired additional roles in brain development in Eutheria, we might speculate that development of novel brain functions during the course of evolution was affected, at least in part, by such structural–functional changes in the SOX3 protein.     

A Survey of Codon and Amino Acid Frequency Bias in Microbial Genomes Focusing on Translational Efficiency

Unequal use of synonymous codons has been found in several prokaryotic and eukaryotic genomes. This bias has been associated with translational efficiency. The prevalence of this bias across lineages is currently unknown. Here, a new method (GCB) to measure codon usage bias is presented. It uses an iterative approach for the determination of codon scores and allows the computation of an index of codon bias suitable for interspecies comparison. A server to calculate GCB-values of individual genes as well as a list of compiled results are available at . The method was applied to complete bacterial genomes. The relation of codon usage bias with amino acid composition and the choice of stop codons were determined and discussed.     

密码对的使用与基因组进化

以5种真核、20种细菌、10种古菌生物的基因组为样本,分析了编码序列中密码对和基因间序列中三联体对的相对模式数随频数的分布,验证了这种分布符合Γ(α,β)分布。发现分布形状参数!值与生物基因组进化存在明显的相关性;编码序列与基因间序列的进化方式截然不同。随着进化,编码序列的分布形状逐渐向随机分布靠近(α值逐渐增大)。而对基因间序列,古菌与真核生物的分布形状接近,与细菌的分布相差明显。     

Complete Amino Acid Sequence of the Sweet Protein Monellin

The sweet protein monellin consists of two noncovalently associated polypeptide chains, the A chain of 44 amino acid residues and the B chain of 50 residues. Two different primary structures have been reported for each of these chains. The complete amino acid sequence of monellin was determined by a combination of FAB- and ESI-mass spectrometry, and by automatic Edman degradation.