The haloarchaeon Halorubrum lacusprofundi is among the few polyextremophilic organisms capable of surviving in one of the most extreme aquatic environments on Earth, the Deep Lake of Antarctica (−18 °C to +11.5 °C and 21–28%, w/v salt content). Hence, H. lacusprofundi has been proposed as a model for biotechnology and astrobiology to investigate potential life beyond Earth. To understand the mechanisms that allow proteins to adapt to both salinity and cold, we structurally (including X-ray crystallography and molecular dynamics simulations) and functionally characterized the β-galactosidase from H. lacusprofundi (hla_bga). Recombinant hla_bga (produced in Haloferax volcanii) revealed exceptional stability, tolerating up to 4 M NaCl and up to 20% (v/v) of organic solvents. Despite being cold-adapted, hla_bga was also stable up to 60 °C. Structural analysis showed that hla_bga combined increased surface acidity (associated with halophily) with increased structural flexibility, fine-tuned on a residue level, for sustaining activity at low temperatures. The resulting blend enhanced structural flexibility at low temperatures but also limited protein movements at higher temperatures relative to mesophilic homologs. Collectively, these observations help in understanding the molecular basis of a dual psychrophilic and halophilic adaptation and suggest that such enzymes may be intrinsically stable and functional over an exceptionally large temperature range.

中文翻译：

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了解多盐极端性酶的高盐和冷适应

盐古菌Halorubrum lacusprofundi是少数能够在地球上最极端的水生环境之一南极深湖（−18°C至+11.5°C和21–28％，w / v含盐量）中生存的多极端生物中）。因此，已经提出了H. lacusprofundi作为生物技术和天体生物学的模型，以研究地球以外的潜在生命。为了了解允许蛋白质同时适应盐度和寒冷的机制，我们在结构上（包括X射线晶体学和分子动力学模拟）并在功能上表征了来自豆角嗜血杆菌（hla_bga）的β-半乳糖苷酶。重组hla_bga（在Haloferax volcanii中产生）表现出卓越的稳定性，耐受高达4 M NaCl和高达20％（v / v）的有机溶剂。尽管经过冷适应，hla_bga在高达60°C的温度下也很稳定。结构分析表明，hla_bga将增加的表面酸度（与嗜盐性相关）与增加的结构柔韧性相结合（在残渣水平上进行了微调），以维持低温下的活性。相对于嗜温同源物，所得混合物在低温下增强了结构的柔韧性，但在高温下也限制了蛋白质的运动。总而言之，这些观察有助于理解嗜冷和嗜盐双重适应的分子基础，并暗示这种酶在异常大的温度范围内可能固有地稳定和起作用。