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Maintaining stable native conformation of a protein under a given ecological condition is the prerequisite for survival of organisms. Extremophilic bacteria and archaea have evolved to adapt under extreme conditions of temperature, pH, salt, and pressure. Molecular adaptations of proteins under these conditions are essential for their survival. These organisms have the capability to maintain stable, native conformations of proteins under extreme conditions. The enzymes produced by the extremophiles are also known as extremozyme, which are used in several industries. Stability and functionality of extremozymes under varying temperature, pH, and solvent conditions are the most desirable requirement of industry. α-Amylase is one of the most important enzymes used in food, pharmaceutical, textile, and detergent industries. This enzyme is produced by diverse microorganisms including various extremophiles. Therefore, understanding its stability is important from fundamental as well as an applied point of view. Each class of extremophiles has a distinctive set of dominant non-covalent interactions which are important for their stability. Static information obtained by comparative analysis of amino acid sequence and atomic resolution structure provides information on the prevalence of particular amino acids or a group of non-covalent interactions. Protein folding studies give the information about thermodynamic and kinetic stability in order to understand dynamic aspect of molecular adaptations. In this review, we have summarized information on amino acid sequence, structure, stability, and adaptability of α-amylases from different classes of extremophiles.
Maintaining stable native conformation of a protein under a given ecological condition is the prerequisite for survival of organisms. Extremophilic bacteria and archaea have evolved to adapt under extreme conditions of temperature, pH, salt, and pressure. Molecular adaptations of proteins under these conditions are essential for their survival. These organisms have the capability to maintain stable, native conformations of proteins under extreme conditions. The enzymes produced by the extremophiles are also known as extremozyme, which are used in several industries. Stability and functionality of extremozymes under varying temperature, pH, and solvent conditions are the most desirable requirement of industry. α-Amylase is one of the most important enzymes used in food, pharmaceutical, textile, and detergent industries. This enzyme is produced by diverse microorganisms including various extremophiles. Therefore, understanding its stability is important from fundamental as well as an applied point of view. Each class of extremophiles has a distinctive set of dominant non-covalent interactions which are important for their stability. Static information obtained by comparative analysis of amino acid sequence and atomic resolution structure provides information on the prevalence of particular amino acids or a group of non-covalent interactions. Protein folding studies give the information about thermodynamic and kinetic stability in order to understand dynamic aspect of molecular adaptations. In this review, we have summarized information on amino acid sequence, structure, stability, and adaptability of α-amylases from different classes of extremophiles.
GtfC-type 4,6-α-glucanotransferase (α-GT) enzymes from Glycoside Hydrolase Family 70 (GH70) are of interest for the modification of starch into low-glycemic index food ingredients. Compared to the related GH70 GtfB-type α-GTs, found exclusively in lactic acid bacteria (LAB), GtfCs occur in non-LAB, share low sequence identity, lack circular permutation of the catalytic domain, and feature a single-segment auxiliary domain IV and auxiliary C-terminal domains. Despite these differences, the first crystal structure of a GtfC, GbGtfC-ΔC from Geobacillus 12AMOR1, and the first one representing a non-permuted GH70 enzyme, reveals high structural similarity in the core domains with most GtfBs, featuring a similar tunneled active site. We propose that GtfC (and related GtfD) enzymes evolved from starch-degrading α-amylases from GH13 by acquiring α-1,6 transglycosylation capabilities, before the events that resulted in circular permutation of the catalytic domain observed in other GH70 enzymes (glucansucrases, GtfB-type α-GTs). AlphaFold modeling and sequence alignments suggest that the GbGtfC structure represents the GtfC subfamily, although it has a so far unique alternating α-1,4/α-1,6 product specificity, likely determined by residues near acceptor binding subsites +1/+2.
: Macromolecular restrained refinement is nowadays the most used method for improving the agreement between an atomic structural model and experimental data. Restraint dictionaries, a key tool behind the success of the method, allow fine-tuning geometric properties such as distances and angles between atoms beyond simplistic expectations. Dictionary generators can provide restraint target estimates derived from different sources, from fully theoretical to experimental and any combination in between. Carbohydrates are stereochemically complex biomolecules and, in their pyranose form, have clear conformational preferences. As such, they pose unique problems to dictionary generators and in the course of this study, require special attention from software developers. Functional differences between restraint generators will be discussed, as well as the process of achieving consistent results with different software designs. The study will conclude a set of practical considerations, as well as recommendations for the generation of new restraint dictionaries, using the improved software alternatives discussed.
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