Exploring the evolution of standard amino-acid alphabet: When genomics meets thermodynamics

Screening of the candidate inhibitory peptides of subtilisin by in vitro RNA display technique

The application of inhibitors facilitates the stable preservation of enzyme in liquid detergent by mitigating the proteolytic activity of subtilisin. The conventionally used subtilisin inhibitors such as boric acid pose a threat to the environment and human health. Thus, the formulation of novel subtilisin inhibitors demands immediate attention. In the current study, we have screened the peptide inhibitors for subtilisin by employing the in vitro mRNA display technique. It is a sensitive screening technique with a high library capacity. The affinity screening was performed between the biotin-modified subtilisin immobilized on the streptavidin magnetic beads and the cDNA-mRNA-peptide fusion molecular library acquired from the in vitro translation and reverse transcription. The candidate peptides with high affinity were obtained after multiple rounds of screening. Furthermore, the inhibitory effect was evaluated, showing that some candidate peptides had inhibitory effects, but the isothermal titration calorimetry and time dependent experiments ultimately proved that these candidate peptides were not stable inhibitors. However, the in vitro mRNA display method explored in this study can be used as a preliminary screening method to provide candidate peptides for the screening of subtilisin inhibitors.

Cofactors as Molecular Fossils To Trace the Origin and Evolution of Proteins

Due to their early origin and extreme conservation, cofactors are valuable molecular fossils for tracing the origin and evolution of proteins. First, as the order of protein folds binding with cofactors roughly coincides with protein-fold chronology, cofactors are considered to have facilitated the origin of primitive proteins by selecting them from pools of random amino acid sequences. Second, in the subsequent evolution of proteins, cofactors still played an important role. More interestingly, as metallic cofactors evolved with geochemical variations, some geochemical events left imprints in the chronology of protein architecture; this provides further evidence supporting the coevolution of biochemistry and geochemistry. In this paper, we attempt to review the molecular fossils used in tracing the origin and evolution of proteins, with a special focus on cofactors.

ATP selection in a random peptide library consisting of prebiotic amino acids

Based upon many theoretical findings on protein evolution, we proposed a ligand-selection model for the origin of proteins, in which the most ancient proteins originated from ATP selection in a pool of random peptides. To test this ligand-selection model, we constructed a random peptide library consisting of 15 types of prebiotic amino acids and then used cDNA display to perform six rounds of in vitro selection with ATP. By means of next-generation sequencing, the most prevalent sequence was defined. Biochemical and biophysical characterization of the selected peptide showed that it was stable and foldable and had ATP-hydrolysis activity as well.

Beyond terrestrial biology: charting the chemical universe of α-amino acid structures

α-Amino acids are fundamental to biochemistry as the monomeric building blocks with which cells construct proteins according to genetic instructions. However, the 20 amino acids of the standard genetic code represent a tiny fraction of the number of α-amino acid chemical structures that could plausibly play such a role, both from the perspective of natural processes by which life emerged and evolved, and from the perspective of human-engineered genetically coded proteins. Until now, efforts to describe the structures comprising this broader set, or even estimate their number, have been hampered by the complex combinatorial properties of organic molecules. Here, we use computer software based on graph theory and constructive combinatorics in order to conduct an efficient and exhaustive search of the chemical structures implied by two careful and precise definitions of the α-amino acids relevant to coded biological proteins. Our results include two virtual libraries of α-amino acid structures corresponding to these different approaches, comprising 121 044 and 3 846 structures, respectively, and suggest a simple approach to exploring much larger, as yet uncomputed, libraries of interest.

Prot-Prop: J-tool to predict the subcellular location of proteins based on physiochemical characterization

PROT-PROP is a computational tool to characterize 27 physicochemical properties of a protein along with its subcellular location (intra or extra) in a single-window application. Other significant features of this software include calculation of numerical values for hydrophobicity, hydrophilicity; composition of small and large amino acids; net hydrophobic content in terms of low/high; and Navie's algorithm to calculate theoretical pI. PROT-PROP is an easy-to-install platform independent implementation of JAVA under a user-friendly interface. It is a standalone version as a virtual appliance and source code for platforms supporting Java 1.5.0 and higher versions, and downloadable from the web http://www.mzu.edu.in/schools/biotechnology.html . PROT-PROP can run under Windows and Macintosh Operating Systems. PROT-PROP is distributed with its source code so that it may be adapted or customized, if desired.

Did evolution select a nonrandom "alphabet" of amino acids?

The last universal common ancestor of contemporary biology (LUCA) used a precise set of 20 amino acids as a standard alphabet with which to build genetically encoded protein polymers. Considerable evidence indicates that some of these amino acids were present through nonbiological syntheses prior to the origin of life, while the rest evolved as inventions of early metabolism. However, the same evidence indicates that many alternatives were also available, which highlights the question: what factors led biological evolution on our planet to define its standard alphabet? One possibility is that natural selection favored a set of amino acids that exhibits clear, nonrandom properties-a set of especially useful building blocks. However, previous analysis that tested whether the standard alphabet comprises amino acids with unusually high variance in size, charge, and hydrophobicity (properties that govern what protein structures and functions can be constructed) failed to clearly distinguish evolution's choice from a sample of randomly chosen alternatives. Here, we demonstrate unambiguous support for a refined hypothesis: that an optimal set of amino acids would spread evenly across a broad range of values for each fundamental property. Specifically, we show that the standard set of 20 amino acids represents the possible spectra of size, charge, and hydrophobicity more broadly and more evenly than can be explained by chance alone.

Bioinformatic identification of the most ancient copper protein architecture

Since copper ions participate in many cellular processes and are implicated in pathogenesis of many diseases, copper proteins have important biological significance. Thus, it is of interest to explore their origins, especially to address the following question: which is the most ancient architecture of copper proteins? In this paper, through analyzing the architectural features of copper proteins, we find that the fold-domain relationship of these proteins follows a power law, which can be explained by preferential attachment principle and implicates that the architecture of the most ancient copper proteins belonged to Cupredoxin-like (b.6) fold. According to the chronology of protein folds, this architecture originated rather late, which can be understood in terms of the low abundance of reducing amino acids (e.g., His, Cys and/or Met) in the primordial world, because these amino acids are required by copper proteins to bind copper ions.

Organic cofactors participated more frequently than transition metals in redox reactions of primitive proteins

Protein redox reactions are one of the most basic and important biochemical actions. As amino acids are weak redox mediators, most protein redox functions are undertaken by protein cofactors, which include organic ligands and transition metal ions. Since both kinds of redox cofactors were available in the pre-protein RNA world, it is challenging to explore which one was more involved in redox processes of primitive proteins? In this paper, using an examination of the redox cofactor usage of putative ancient proteins, we infer that organic ligands participated more frequently than transition metals in redox reactions of primitive proteins, at least as protein cofactors. This is further supported by the relative abundance of amino acids in the primordial world. Supplementary material for this article can be found on the BioEssays website.

Estimating the "steric clash" at cis peptide bonds

To account for the scarcity of cis peptide bonds in proteins, especially in nonproline (or secondary amide) cases, a steric-clash argument is often put forward, in a scheme where the R lateral chains are facing parallel one another, and the backbone is kept in an "all- trans"-like arrangement. Although such a steric conflict can be partly relieved through proper adjustment of the backbone dihedral angles, one can try to estimate its associated energy cost. To this end, quantum-chemistry approaches using a differential-torsion protocol and bond-separation-energy analyses are applied to N-ethyl propionamide CH3-CH2-CO-NH-CH2-CH3, regarded as a model capable of exhibiting C beta...C beta interaction as in alanine succession. The calculations provide an increment of 9 kcal/mol, quite close to that obtained in the nearly isostere (gsg) rotamer of n-hexane (10 kcal/mol), suggesting the local effects induced by methyl-methyl contact are similar in both cases. Analogous treatments on larger radicals as encountered in leucine or phenylalanine dimers do not change this increment much, which therefore defines the basic reference per-plaque quota to be overcome along all- cis chains. Explicit modeling indicated it can be reduced by up to a factor of 4.

Distribution patterns of small-molecule ligands in the protein universe and implications for origin of life and drug discovery

Ligand-protein mapping was found to follow a power law and the preferential attachment principle, leading to the identification of the molecules, mostly nucleotide-containing compounds, that are likely to have evolved earliest.

Background

Extant life depends greatly on the binding of small molecules (such as ligands) with macromolecules (such as proteins), and one ligand can bind multiple proteins. However, little is known about the global patterns of ligand-protein mapping.

Results

By examining 2,186 well-defined small-molecule ligands and thousands of protein domains derived from a database of druggable binding sites, we show that a few ligands bind tens of protein domains or folds, whereas most ligands bind only one, which indicates that ligand-protein mapping follows a power law. Through assigning the protein-binding orders (early or late) for bio-ligands, we demonstrate that the preferential attachment principle still holds for the power-law relation between ligands and proteins. We also found that polar molecular surface area, H-bond acceptor counts, H-bond donor counts and partition coefficient are potential factors to discriminate ligands from ordinary molecules and to differentiate super ligands (shared by three or more folds) from others.

Conclusion

These findings have significant implications for evolution and drug discovery. First, the chronology of ligand-protein binding can be inferred by the power-law feature of ligand-protein mapping. Some nucleotide-containing ligands, such as ATP, ADP, GDP, NAD, FAD, dihydro-nicotinamide-adenine-dinucleotide phosphate (NDP), nicotinamide-adenine-dinucleotide phosphate (NAP), flavin mononucleotide (FMN) and AMP, are found to be the earliest cofactors bound to proteins, agreeing with the current understanding of evolutionary history. Second, the finding that about 30% of ligands are shared by two or more domains will help with drug discovery, such as in finding new functions from old drugs, developing promiscuous drugs and depending more on natural products.

Characters of very ancient proteins

Tracing the characters of very ancient proteins represents one of the biggest challenges in the study of origin of life. Although there are no primitive protein fossils remaining, the characters of very ancient proteins can be traced by molecular fossils embedded in modern proteins. In this paper, first the prior findings in this area are outlined and then a new strategy is proposed to address the intriguing issue. It is interesting to find that various molecular fossils and different protein datasets lead to similar conclusions on the features of very ancient proteins, which can be summarized as follows: (i) the architectures of very ancient proteins belong to the following folds: P-loop containing nucleoside triphosphate hydrolases (c.37), TIM beta/alpha-barrel (c.1), NAD(P)-binding Rossmann-fold domains (c.2), Ferredoxin-like (d.58), Flavodoxin-like (c.23) and Ribonuclease H-like motif (c.55); (ii) the functions of very ancient proteins are related to the metabolisms of purine, pyrimidine, porphyrin, chlorophyll and carbohydrates; (iii) a certain part of very ancient proteins need cofactors (such as ATP, NADH or NADPH) to work normally.