DR1769, a Protein with N-Terminal Beta Propeller Repeats and a Low-Complexity Hydrophilic Tail, Plays a Role in Desiccation Tolerance of Deinococcus radiodurans

Abstract

The Deinococcus radiodurans genome encodes five putative quinoproteins. Among these, the ⌬dr2518 and ⌬dr1769 mutants became sensitive to gamma radiation. DR2518 with beta propeller repeats in the C-terminal domain was characterized as a radiation-responsive serine/threonine protein kinase in this bacterium. DR1769 contains beta propeller repeats at the N terminus, while its C-terminal domain is a proline-rich disordered structure and constitutes a low-complexity hydrophilic region with aliphatic-proline dipeptide motifs. The ⌬dr1769 mutant showed nearly a 3-log cycle sensitivity to desiccation at 5% humidity compared to that of the wild type. Interestingly, the gamma radiation and mitomycin C (MMC) resistance in mutant cells also dropped by ϳ1-log cycle at 10 kGy and ϳ1.5-fold, respectively, compared to those in wild-type cells. But there was no effect of UV (254 nm) exposure up to 800 J · m ؊2 . These cells showed defective DNA double-strand break repair, and the average size of the nucleoid in desiccated wild-type and ⌬dr1769 cells was reduced by approximately 2-fold compared to that of respective controls. However, the nucleoid in wild-type cells returned to a size almost similar to that of the untreated control, which did not happen in mutant cells, at least up to 24 h postdesiccation. These results suggest that DR1769 plays an important role in desiccation and radiation resistance of D. radiodurans, possibly by protecting genome integrity under extreme conditions. D esiccation is one of the most hostile conditions that impose physiological constraints, which few organisms can tolerate. Desiccation causes both reversible and irreversible changes in cellular milieus, including protein aggregation, membrane fusion, and damages to DNA, RNA, and proteins (1, 2). In spite of this, there are many organisms that can tolerate prolonged desiccation by entering in the desiccation dormant state and/or protecting cells from the effects of extensive water loss. The roles of disaccharides and certain proteins, like anhydrin and late embryogenesis abundant (LEA)-related proteins, have been reported in the desiccation tolerance of invertebrates (3) and plants (4, 5). The LEA proteins are characterized as having the proline-and glycine-rich low-complexity (LC) regions, which form unstructured conformation under normal physiological conditions. Upon desiccation, these sequences undergo structural transition from an unstructured conformation to a well-defined and functionally viable structure (3, 6). The mechanisms through which these amino acids could contribute to desiccation tolerance are not very clear. However, it has been shown that disordered hydrophilic regions could retain ϳ20 times more water than globular proteins of nearly similar sizes, which upon anhydrobiosis leads to the conformational change from a poly-proline type II helix into an ␣ helix (7). An alternative hypothesis also suggests that the side chains of polar amino acids in the LC region could mimic the nature of a water molecule and provide chaperone-lik...

Functional assessment of hydrophilic domains of late embryogenesis abundant proteins from distant organisms

“…Escherichia coli recombinant strain cultures were induced with IPTG at a final optimal concentration of 0.1 mM for 4 h, and the cells were desiccated and treated with H 2 O 2 as previously described (Rajpurohit and Misra, ; Jiang et al ., ; Wang et al ., ). Different serial dilutions of these cells were plated onto LB agar plates and incubated at 37°C for 1 day before colonies were observed and counted.…”

“…Both desiccation and oxidation are widely studied extreme processes that are detrimental to the growth of organisms because they induce protein aggregation and nucleic acid damage (Rajpurohit and Misra, ; Atashgahi et al ., ). Moreover, recent advancements have shown that the organismal responses to both stresses are similar, indicating that the mechanisms for protecting crucial biomolecules from damage are related (Fredrickson et al ., ; Chakrabortee et al ., ).…”

“…Structural exploration of G3LEA proteins using circular dichroism (CD) indicated that they are randomly coiled in aqueous solution but adopt a largely α‐helical conformation in the presence of glycerol or after desiccation, which is considered to be the prerequisite for LEA‐macromolecule interactions for protection under stresses (Tolleter et al ., ). Although many studies implicated that the hydrophilic regions of LEA proteins were crucial to achieve their structural transformation that contributes to the organisms’ stress tolerance acquisition (Haaning et al ., ; Rajpurohit and Misra, ; Cuevas‐Velazquez et al ., ), details of the function of this hydrophilic region remain unclear. Additionally, previous work highlighted the importance of G3LEA protein motifs from soybean that contribute to their enhanced salt resistance (Liu and Zheng, ).…”

A tamB homolog is involved in maintenance of cell envelope integrity and stress resistance of Deinococcus radiodurans

“…To date, more than 50 species of the Deinococcus genus have been identified in a variety of environments18. Deinococcus are distinguished by their extraordinary tolerance to a number of lethal agents including ionizing radiation, hydrogen peroxide, osmotic pressure, desiccation, UV radiation and mitomycin C (MMC)19202122. It is widely accepted that efficient DNA repair systems and cell defence systems including an unusual cell envelope and small molecule antioxidants (e.g.…”

Signal Recognition Particle RNA Contributes to Oxidative Stress Response in Deinococcus radiodurans by Modulating Catalase Localization

“…Among these eight proteins, DR_1998/KatE1 and DR_A0259/KatE2 are the two catalases that exhibit activity in D. radiodurans (75), and DR_A0202/SodC is a Cu/Zn-dependent superoxide dismutase that catalyzes the conversion of metabolic superoxide (O 2 − ) radicals to H 2 O 2 (Lim et al, 2019). Of the remaining five proteins, DR_1769 is a conserved protein present in all Deinococcus species with a regulatory role in resistance to desiccation and gamma radiation (Rajpurohit and Misra, 2013;Lim et al, 2019). DR_1736 is a nuclease involved in DNA repair, which processes DNA to generate 3' overhang fragments for the further recombination with near homologous fragments (Kota and Misra, 2013).…”