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Karyopherins and Nuclear actin transport
Immanuel Dhanasingh,Jin Myung Choi,Sung Haeng Lee 한국구조생물학회 2015 Biodesign Vol.3 No.2
Although compartmentalization of a eukaryotic cell into the nucleus and cytoplasm has benefits, it further necessitates transport between the two compartments. Active transport between these two compartments requires metabolic energy and transporter proteins. Nuclear transporter receptors belong to the karyopherin super family and aid in the movement of cargo into (importers) or out of the nucleus (exporters) or are bidirectional. Presence of actin in nucleus and its nuclear trafficking remains intriguing due to its lack of nuclear import or export signals. Despite the fact that importin-9 and exportin-6 have been linked to nuclear import and export of actin respectively, the mechanistic details about actin-karyopherin interaction are not known yet. In this review, we compared the structural details of already available karyopherins and provide the initial structural prediction for exportin-6. The WH2 domain from diverse actin binding proteins display a similar architecture of N-terminal α helix followed by the LKKT(V) motif. A similar LKPS motif was identified near helix 14A of exportin-6, which might be the binding site for actin. Based on these predictions, we have postulated a mechanism of actin-karyopherin interaction.
Immanuel Dhanasingh,Eunsil Choi,Jihwan Hwang,Sung Haeng Lee 한국구조생물학회 2018 Biodesign Vol.6 No.1
Toxin–antitoxin (TA) systems are ubiquitous among most of prokaryotes and govern the cell death or growth arrest in response to environmental cues. TA systems are associated with adaptation of pathogens to unfavorable environments, indicating their potential as a target for antibiotics. Here, we purified and crystallized the TA complex from the extremophile Deinococcus radiodurans. The TA complex (DrMazEF) was co-expressed and pulled using the N-terminal glutathione S-transferase-tagged DrMazF. The complex was crystallized in 100 mM citric acid pH 3.5 containing 25% PEG3350. The crystal diffracted X-ray to a 2.6 Å resolution and belonged to the space group P212121, with the unit cell parameters a =46.01, b = 74.04, and c = 138.26 Å. The asymmetric unit of the crystal had six molecules in two heterotrimeric complexes with a calculated Mathew’s coefficient of 1.84 Å3 Da-1 and a solvent content of 33.18%.
Immanuel Dhanasingh,Eunsil Choi,Jeongeun Lee,Sung Haeng Lee,황지환 한국미생물학회 2021 The journal of microbiology Vol.59 No.2
In prokaryotes, toxin-antitoxin (TA) systems are commonly found. They likely reflect the adaptation of pathogenic bacteria or extremophiles to various unfavorable environments by slowing their growth rate. Genomic analysis of the extremophile Deinococcus radiodurans R1 revealed the presence of eight type II TA systems, including the genes dr0417, dr0660, dr1530, dr0690, and dr1807. Expression of these toxin genes led to inhibition of Escherichia coli growth, whereas their antidote antitoxins were able to recover the growth defect. Remarkably, Dr0417 (DrMazF) showed endoribonuclease activity toward rRNAs as well as mRNAs, as determined by in vivo and in vitro RNA cleavage assays, and this activity was inhibited by Dr0416 (DrMazE). It was also found that the expression of dr0416-0417 module is directly regulated by the DrMazE-MazF complex. Furthermore, this TA module was induced under stress conditions and plays an important role in survival. To understand the regulatory mechanism at the molecular level, we determined the first high-resolution structures of DrMazF alone and of the DrMazE-MazF complex. In contrast with the hetero-hexameric state of typical MazEMazF complexes found in other species, DrMazE-MazF crystal structure consists of a hetero-trimer, with the DNA-binding domain of DrMazE undergoing self-cleavage at the flexible linker loop. Our structure revealed that the unique residue R54 provides an additional positive charge to the substratebinding pocket of DrMazF, its mutation significantly affects the endonuclease activity. Thus, our work reports the unique structural and biochemical features of the DrMazE-MazF system.