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The MAP kinase HwHog1 from the halophilic black yeast Hortaea werneckii: coping with stresses in solar salterns.

Lenassi M, Vaupotic T, Gunde-Cimerman N, Plemenitas A - Saline Syst. (2007)

Bottom Line: Identification of HOG1-like genes from other halotolerant fungi isolated from solar salterns demonstrates a high degree of similarity and excellent phylogenetic clustering with orthologues of fungal origin.The HOG signalling pathway has an important role in sensing and responding to hyper-osmolar, oxidative and high-temperature stresses in the halophilic fungi H. werneckii.These findings are an important advance in our understanding of the HOG pathway response to stress in H. werneckii, a proposed model organism for studying the salt tolerance of halophilic and halotolerant eukaryotes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Vrazov trg 2, Ljubljana, Slovenia. metka.lenassi@mf.uni-lj.si

ABSTRACT

Background: Hortaea werneckii is one of the most salt-tolerant species among microorganisms. It has been isolated from hypersaline waters of salterns as one of the predominant species of a group of halophilic and halotolerant melanized yeast-like fungi, arbitrarily named as "black yeasts". It has previously been shown that H. werneckii has distinct mechanisms of adaptation to high salinity environments that are not seen in salt-sensitive and only moderately salt-tolerant fungi. In H. werneckii, the HOG pathway is important for sensing the changes in environmental osmolarity, as demonstrated by identification of three main pathway components: the mitogen-activated protein kinase (MAPK) HwHog1, the MAPK kinase HwPbs2, and the putative histidine kinase osmosensor HwHhk7.

Results: In this study, we show that the expression of HwHOG1 in salt-adapted cells depends on the environmental salinity and that HwHOG1 transcription responds rapidly but reciprocally to the acute hyper-saline or hypo-saline stress. Molecular modelling of HwHog1 reveals an overall structural homology with other MAPKs. HwHog1 complements the function of ScHog1 in the Saccharomyces cerevisiae multistress response. We also show that hyper-osmolar, oxidative and high-temperature stresses activate the HwHog1 kinase, although under high-temperature stress the signal is not transmitted via the MAPK kinase Pbs2. Identification of HOG1-like genes from other halotolerant fungi isolated from solar salterns demonstrates a high degree of similarity and excellent phylogenetic clustering with orthologues of fungal origin.

Conclusion: The HOG signalling pathway has an important role in sensing and responding to hyper-osmolar, oxidative and high-temperature stresses in the halophilic fungi H. werneckii. These findings are an important advance in our understanding of the HOG pathway response to stress in H. werneckii, a proposed model organism for studying the salt tolerance of halophilic and halotolerant eukaryotes.

No MeSH data available.


Related in: MedlinePlus

Three-dimensional model of HwHog1. Superposition of HwHog1 (green) and murine p38 (blue). (A) Ribbon diagram of the conservation of secondary structure elements. The position of the phosphorylation Lip region of HwHog1 is shown (orange). (B) Surface view of the HwHog1 protein. The conserved CD domain (red) and the phosphorylation Lip (orange) are exposed on the surface at opposite sides of the protein. (C) The architecture of the phosphorylation Lip, and (D) the CD domain amino-acid residues are represented by sticks. The positions of the phosphorylation site residues Thr171 and Tyr173 are marked. The negatively charged Asp304, Asp307 and Glu308 amino acids in the CD domain of HwHog1 are denoted by red sticks. The amino-acid residue conservation between the HwHog1 and p38 sequences is denoted by red boxes. The plots were created with the PyMOL programme (version 0.97 [35]).
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Figure 2: Three-dimensional model of HwHog1. Superposition of HwHog1 (green) and murine p38 (blue). (A) Ribbon diagram of the conservation of secondary structure elements. The position of the phosphorylation Lip region of HwHog1 is shown (orange). (B) Surface view of the HwHog1 protein. The conserved CD domain (red) and the phosphorylation Lip (orange) are exposed on the surface at opposite sides of the protein. (C) The architecture of the phosphorylation Lip, and (D) the CD domain amino-acid residues are represented by sticks. The positions of the phosphorylation site residues Thr171 and Tyr173 are marked. The negatively charged Asp304, Asp307 and Glu308 amino acids in the CD domain of HwHog1 are denoted by red sticks. The amino-acid residue conservation between the HwHog1 and p38 sequences is denoted by red boxes. The plots were created with the PyMOL programme (version 0.97 [35]).

Mentions: To further examine the possible rearrangements of these key structural elements of HwHog1p, the three-dimensional (3D) model of the full-length HwHog1 protein was calculated using the MODELLER programme [25], based on crystallographic structure of murine p38 MAPK as a template [26], a functional and structural homologue of S. cerevisiae Hog1. This approach to comparative protein modelling was based on the satisfaction of spatial restraints [27] implemented in the MODELLER programme. Since the template structure for homology-based modelling was more than 40% identical to the sequence of the target (47.43% homology), the model created should have about 90% of the main-chain atoms comparable with the X-ray structure [25]. This calculated 3D model of the structure of HwHog1 demonstrated the well defined overall fold of the MAP kinase superfamily. The superposition of the HwHog1 model on the murine p38 template revealed a strong overlap, particularly within the conserved regions and with the active-site amino-acid residues of the phosphorylation "Lip" (Fig. 2A). Compared to the template structure, the topologically less overlapping region is a portion in the N-terminal domain that consists mainly of β-sheets. The phosphorylation Lip and the docking groove (CD domain) are exposed on opposite sides of the protein surface (Fig. 2B). The phosphorylation Lip in HwHog1 (LARIQDPQMTGYV) consists of 13 amino-acid residues (Fig. 2C), exactly as does the Lip in p38 (LARHTDDEMTGYV). The structural positioning of the critical phosphorylation residues of Thr171 and Tyr173 within the Lip of HwHog1 shows complete steric agreement with Thr180 and Tyr182 of p38, although these Lip regions share only 69% amino-acid identity. There is also an excess net negative charge in the p38 Lip as compared with the HwHog1 Lip, due to the absence of glutamate and aspartate in this region of HwHog1. Although the HwHog1 contains a proline residue in the phosphorylation Lip, this does not disturb the architecture of the Lip. Therefore, the phosphorylation site sequence of Thr171-Gly172-Tyr173 makes the essential surface turn.


The MAP kinase HwHog1 from the halophilic black yeast Hortaea werneckii: coping with stresses in solar salterns.

Lenassi M, Vaupotic T, Gunde-Cimerman N, Plemenitas A - Saline Syst. (2007)

Three-dimensional model of HwHog1. Superposition of HwHog1 (green) and murine p38 (blue). (A) Ribbon diagram of the conservation of secondary structure elements. The position of the phosphorylation Lip region of HwHog1 is shown (orange). (B) Surface view of the HwHog1 protein. The conserved CD domain (red) and the phosphorylation Lip (orange) are exposed on the surface at opposite sides of the protein. (C) The architecture of the phosphorylation Lip, and (D) the CD domain amino-acid residues are represented by sticks. The positions of the phosphorylation site residues Thr171 and Tyr173 are marked. The negatively charged Asp304, Asp307 and Glu308 amino acids in the CD domain of HwHog1 are denoted by red sticks. The amino-acid residue conservation between the HwHog1 and p38 sequences is denoted by red boxes. The plots were created with the PyMOL programme (version 0.97 [35]).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1828057&req=5

Figure 2: Three-dimensional model of HwHog1. Superposition of HwHog1 (green) and murine p38 (blue). (A) Ribbon diagram of the conservation of secondary structure elements. The position of the phosphorylation Lip region of HwHog1 is shown (orange). (B) Surface view of the HwHog1 protein. The conserved CD domain (red) and the phosphorylation Lip (orange) are exposed on the surface at opposite sides of the protein. (C) The architecture of the phosphorylation Lip, and (D) the CD domain amino-acid residues are represented by sticks. The positions of the phosphorylation site residues Thr171 and Tyr173 are marked. The negatively charged Asp304, Asp307 and Glu308 amino acids in the CD domain of HwHog1 are denoted by red sticks. The amino-acid residue conservation between the HwHog1 and p38 sequences is denoted by red boxes. The plots were created with the PyMOL programme (version 0.97 [35]).
Mentions: To further examine the possible rearrangements of these key structural elements of HwHog1p, the three-dimensional (3D) model of the full-length HwHog1 protein was calculated using the MODELLER programme [25], based on crystallographic structure of murine p38 MAPK as a template [26], a functional and structural homologue of S. cerevisiae Hog1. This approach to comparative protein modelling was based on the satisfaction of spatial restraints [27] implemented in the MODELLER programme. Since the template structure for homology-based modelling was more than 40% identical to the sequence of the target (47.43% homology), the model created should have about 90% of the main-chain atoms comparable with the X-ray structure [25]. This calculated 3D model of the structure of HwHog1 demonstrated the well defined overall fold of the MAP kinase superfamily. The superposition of the HwHog1 model on the murine p38 template revealed a strong overlap, particularly within the conserved regions and with the active-site amino-acid residues of the phosphorylation "Lip" (Fig. 2A). Compared to the template structure, the topologically less overlapping region is a portion in the N-terminal domain that consists mainly of β-sheets. The phosphorylation Lip and the docking groove (CD domain) are exposed on opposite sides of the protein surface (Fig. 2B). The phosphorylation Lip in HwHog1 (LARIQDPQMTGYV) consists of 13 amino-acid residues (Fig. 2C), exactly as does the Lip in p38 (LARHTDDEMTGYV). The structural positioning of the critical phosphorylation residues of Thr171 and Tyr173 within the Lip of HwHog1 shows complete steric agreement with Thr180 and Tyr182 of p38, although these Lip regions share only 69% amino-acid identity. There is also an excess net negative charge in the p38 Lip as compared with the HwHog1 Lip, due to the absence of glutamate and aspartate in this region of HwHog1. Although the HwHog1 contains a proline residue in the phosphorylation Lip, this does not disturb the architecture of the Lip. Therefore, the phosphorylation site sequence of Thr171-Gly172-Tyr173 makes the essential surface turn.

Bottom Line: Identification of HOG1-like genes from other halotolerant fungi isolated from solar salterns demonstrates a high degree of similarity and excellent phylogenetic clustering with orthologues of fungal origin.The HOG signalling pathway has an important role in sensing and responding to hyper-osmolar, oxidative and high-temperature stresses in the halophilic fungi H. werneckii.These findings are an important advance in our understanding of the HOG pathway response to stress in H. werneckii, a proposed model organism for studying the salt tolerance of halophilic and halotolerant eukaryotes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Vrazov trg 2, Ljubljana, Slovenia. metka.lenassi@mf.uni-lj.si

ABSTRACT

Background: Hortaea werneckii is one of the most salt-tolerant species among microorganisms. It has been isolated from hypersaline waters of salterns as one of the predominant species of a group of halophilic and halotolerant melanized yeast-like fungi, arbitrarily named as "black yeasts". It has previously been shown that H. werneckii has distinct mechanisms of adaptation to high salinity environments that are not seen in salt-sensitive and only moderately salt-tolerant fungi. In H. werneckii, the HOG pathway is important for sensing the changes in environmental osmolarity, as demonstrated by identification of three main pathway components: the mitogen-activated protein kinase (MAPK) HwHog1, the MAPK kinase HwPbs2, and the putative histidine kinase osmosensor HwHhk7.

Results: In this study, we show that the expression of HwHOG1 in salt-adapted cells depends on the environmental salinity and that HwHOG1 transcription responds rapidly but reciprocally to the acute hyper-saline or hypo-saline stress. Molecular modelling of HwHog1 reveals an overall structural homology with other MAPKs. HwHog1 complements the function of ScHog1 in the Saccharomyces cerevisiae multistress response. We also show that hyper-osmolar, oxidative and high-temperature stresses activate the HwHog1 kinase, although under high-temperature stress the signal is not transmitted via the MAPK kinase Pbs2. Identification of HOG1-like genes from other halotolerant fungi isolated from solar salterns demonstrates a high degree of similarity and excellent phylogenetic clustering with orthologues of fungal origin.

Conclusion: The HOG signalling pathway has an important role in sensing and responding to hyper-osmolar, oxidative and high-temperature stresses in the halophilic fungi H. werneckii. These findings are an important advance in our understanding of the HOG pathway response to stress in H. werneckii, a proposed model organism for studying the salt tolerance of halophilic and halotolerant eukaryotes.

No MeSH data available.


Related in: MedlinePlus