Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704 Poznan, Poland.
Department of Biology, Section of Biochemistry and Molecular Biology, National and Kapodistrian University of Athens, 15701 Zografou, Greece.
Int J Mol Sci. 2020 Apr 21;21(8):2892. doi: 10.3390/ijms21082892.
Analyzing the structure of proteins from extremophiles is a promising way to study the rules governing the protein structure, because such proteins are results of structural and functional optimization under well-defined conditions. Studying the structure of chitinases addresses an interesting aspect of enzymology, because chitin, while being the world's second most abundant biopolymer, is also a recalcitrant substrate. The crystal structure of a thermostable chitinase from (Chi40) has been solved revealing a β/α-barrel (TIM-barrel) fold with an α+β insertion domain. This is the first chitinase structure of the multi-chitinase system of . The protein is also known to refold efficiently after thermal or chemical denaturation. Chi40 is structurally close to the catalytic domain of psychrophilic chitinase B from TAD20. Differences are noted in comparison to the previously examined chitinases, particularly in the substrate-binding cleft. A comparison of the thermophilic enzyme with its psychrophilic homologue revealed structural features that could be attributed to Chi40's thermal stability: compactness of the structure with trimmed surface loops and unique disulfide bridges, one of which is additionally stabilized by S-π interactions with aromatic rings. Uncharacteristically for thermophilic proteins, Chi40 has fewer salt bridges than its mesophilic and psychrophilic homologues.
分析极端微生物蛋白质的结构是研究蛋白质结构规律的一种很有前途的方法，因为这些蛋白质是在明确条件下进行结构和功能优化的结果。研究几丁质酶的结构涉及到酶学的一个有趣方面，因为几丁质虽然是世界上第二丰富的生物聚合物，但也是一种难以降解的底物。来自 （Chi40）的耐热几丁质酶的晶体结构已经被解决，揭示了一个具有α+β插入结构域的β/α-桶（TIM-桶）折叠。这是 多几丁质酶系统中第一个几丁质酶结构。该蛋白在热或化学变性后也能有效地重新折叠。Chi40 在结构上与来自 TAD20 的嗜冷几丁质酶 B 的催化结构域非常接近。与之前研究的几丁质酶相比，该结构存在差异，特别是在底物结合裂缝处。对嗜热酶与其嗜冷同源物的比较揭示了可能归因于 Chi40 热稳定性的结构特征：结构紧凑，表面环修剪，独特的二硫键，其中一个通过与芳环的 S-π 相互作用进一步稳定。与嗜热蛋白不同，Chi40 的盐桥比其中温和嗜冷同源物少。
