Complete proteins
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Complete Proteins: Synthesis, Classification, and Analysis
In Vitro Synthesis of Complete Proteins
The synthesis of complete proteins in cell-free systems has been a significant milestone in molecular biology. Early work demonstrated that peptide synthesis occurs on the ribosome and requires ATP, GTP, and tRNA. This foundational understanding led to the first successful synthesis of a complete protein, the coat protein of coliphage f2, in a cell-free extract of Escherichia coli. Subsequent studies have utilized viral RNAs to prime the synthesis of complete proteins, although bacterial messengers posed challenges due to their translation dynamics during synthesis.
Automated Flow Chemistry for Protein Synthesis
Recent advancements in automated flow chemistry have enabled the synthesis of fully synthetic proteins. This method overcomes the limitations of traditional solid-phase peptide synthesis, which struggles with peptides longer than 50 amino acids due to inefficient coupling and side reactions. Using an automated fast-flow instrument, researchers have synthesized single-domain proteins up to 164 amino acids long, including enzymes and regulatory factors, with properties comparable to their biologically expressed counterparts.
Phylogenetic Classification of Proteins from Complete Genomes
The Clusters of Orthologous Groups of proteins (COGs) database represents a comprehensive attempt to classify proteins encoded in complete genomes phylogenetically. It includes 2791 COGs with 45,350 proteins from 30 genomes of bacteria, archaea, and yeast. This classification aids in understanding the evolutionary relationships and functional roles of proteins across different organisms.
Estimating Protein Folds and Families
Using complete genome data, researchers have estimated the total number of protein folds and families. The number of globular, water-soluble protein folds is estimated to be around 1000, with structural information available for about one-third of these. The number of protein families with significant sequence conservation ranges between 4000 and 7000, with structures available for about 20% of these families.
Amino Acid Composition and Analysis
The complete analysis of protein amino acids is fundamental to understanding protein structure. Recent studies have presented a comprehensive analysis of simple, crystalline proteins, such as β-lactoglobulin, providing valuable data on their amino acid composition. Additionally, advancements in gas-liquid chromatography have enabled the complete separation of the twenty protein amino acids, facilitating more accurate and efficient analysis.
Enzymic Hydrolysis of Proteins
Complete enzymic hydrolysis of proteins has been achieved using proteolytic enzymes, overcoming the limitations of acid hydrolysis, which can destroy certain amino acids. Early studies demonstrated that enzymes like pepsin, trypsin, and erepsin could degrade proteins to amino acids, but it was only recently that methods employing purified proteolytic enzymes have been developed for complete hydrolysis.
Conclusion
The synthesis, classification, and analysis of complete proteins have seen significant advancements over the years. From the early in vitro synthesis of viral proteins to the modern automated flow chemistry techniques, the field has made remarkable progress. Phylogenetic classification and comprehensive amino acid analysis further enhance our understanding of protein structure and function, paving the way for future research and applications in biotechnology and medicine.
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