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Evolutionary and structural perspectives of plant cyclic nucleotide-gated cation channels.

Zelman AK, Dawe A, Gehring C, Berkowitz GA - Front Plant Sci (2012)

Bottom Line: All eukaryote CNGC polypeptides have a cyclic nucleotide-binding domain and a calmodulin binding domain as well as a six transmembrane/one pore tertiary structure.Additionally, an amino acid motif that is only found in the phosphate binding cassette and hinge regions of plant CNGCs, and is present in all experimentally confirmed CNGCs but no other channels was identified.This CNGC-specific amino acid motif provides an additional diagnostic tool to identify plant CNGCs, and can increase confidence in the annotation of open reading frames in newly sequenced genomes as putative CNGCs.

View Article: PubMed Central - PubMed

Affiliation: Agricultural Biotechnology Laboratory, Department of Plant Science, University of Connecticut Storrs, CT, USA.

ABSTRACT
Ligand-gated cation channels are a frequent component of signaling cascades in eukaryotes. Eukaryotes contain numerous diverse gene families encoding ion channels, some of which are shared and some of which are unique to particular kingdoms. Among the many different types are cyclic nucleotide-gated channels (CNGCs). CNGCs are cation channels with varying degrees of ion conduction selectivity. They are implicated in numerous signaling pathways and permit diffusion of divalent and monovalent cations, including Ca(2+) and K(+). CNGCs are present in both plant and animal cells, typically in the plasma membrane; recent studies have also documented their presence in prokaryotes. All eukaryote CNGC polypeptides have a cyclic nucleotide-binding domain and a calmodulin binding domain as well as a six transmembrane/one pore tertiary structure. This review summarizes existing knowledge about the functional domains present in these cation-conducting channels, and considers the evidence indicating that plant and animal CNGCs evolved separately. Additionally, an amino acid motif that is only found in the phosphate binding cassette and hinge regions of plant CNGCs, and is present in all experimentally confirmed CNGCs but no other channels was identified. This CNGC-specific amino acid motif provides an additional diagnostic tool to identify plant CNGCs, and can increase confidence in the annotation of open reading frames in newly sequenced genomes as putative CNGCs. Conversely, the absence of the motif in some plant sequences currently identified as probable CNGCs may suggest that they are misannotated or protein fragments.

No MeSH data available.


Related in: MedlinePlus

Superimposed images (redrawn from Leng et al., 2002) of the S6 helix and pore domains of the plant (A. thaliana) CNGC2 sequence and the bacterial (Streptomyces lividans) K+-selective channel KcsA (Doyle et al., 1998; PDB record 1BL8A). Threading of the A. thaliana CNGC2 S6 transmembrane helix and pore region through the KcsA structure identifies the residues “AND” as in the ion conducting pathway where the residues “GYG” (shown in pink) that form the ion selectivity filter of a K+-selective channel are positioned. This suggests that plant CNGCs may have a mechanism for cation conductance that is conserved in P-loop channels. In plants, four separate CNGC peptides are presumed to form a tetrameric structure that shares the “inverted teepee” quaternary structure of animal P-loop channels.
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Figure 3: Superimposed images (redrawn from Leng et al., 2002) of the S6 helix and pore domains of the plant (A. thaliana) CNGC2 sequence and the bacterial (Streptomyces lividans) K+-selective channel KcsA (Doyle et al., 1998; PDB record 1BL8A). Threading of the A. thaliana CNGC2 S6 transmembrane helix and pore region through the KcsA structure identifies the residues “AND” as in the ion conducting pathway where the residues “GYG” (shown in pink) that form the ion selectivity filter of a K+-selective channel are positioned. This suggests that plant CNGCs may have a mechanism for cation conductance that is conserved in P-loop channels. In plants, four separate CNGC peptides are presumed to form a tetrameric structure that shares the “inverted teepee” quaternary structure of animal P-loop channels.

Mentions: As indicated above, the quaternary structure of a member of the P-loop channel family is dependent on the assembly of four gene products in some cases (e.g., in animal and plant K+-selective voltage-gated channels) where only one P-loop “cassette” is encoded by the gene (i.e. S1–S6 with the P-loop between S5 and S6). It is therefore conceivable that plant CNGC channel complexes are formed by the assembly of four polypeptides, with each polypeptide corresponding to a structure similar to that shown in Figure 1B. Threading regions (S6 and pore loop, an example is shown in Figure 3 below) of plant CNGC coding sequences through the crystal structure of a quaternary P-loop channel indicates that the plant CNGC polypeptide may be capable of forming the tetrameric structure common to P-loop channels (Hua et al., 2003b). However, this model has not been verified experimentally. It should be noted that functional animal CNGC channel proteins are in all cases generated from such a tetrameric assembly of P-loop cassette polypeptides (Zheng and Zagotta, 2004) and that plant and animal CNGC polypeptides share a similar general S1–S6 topography. Thus, the aforementioned conjecture about the tetrameric structure of plant CNGCs is entirely consistent with the general concept of ion channel assembly and function.


Evolutionary and structural perspectives of plant cyclic nucleotide-gated cation channels.

Zelman AK, Dawe A, Gehring C, Berkowitz GA - Front Plant Sci (2012)

Superimposed images (redrawn from Leng et al., 2002) of the S6 helix and pore domains of the plant (A. thaliana) CNGC2 sequence and the bacterial (Streptomyces lividans) K+-selective channel KcsA (Doyle et al., 1998; PDB record 1BL8A). Threading of the A. thaliana CNGC2 S6 transmembrane helix and pore region through the KcsA structure identifies the residues “AND” as in the ion conducting pathway where the residues “GYG” (shown in pink) that form the ion selectivity filter of a K+-selective channel are positioned. This suggests that plant CNGCs may have a mechanism for cation conductance that is conserved in P-loop channels. In plants, four separate CNGC peptides are presumed to form a tetrameric structure that shares the “inverted teepee” quaternary structure of animal P-loop channels.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3362136&req=5

Figure 3: Superimposed images (redrawn from Leng et al., 2002) of the S6 helix and pore domains of the plant (A. thaliana) CNGC2 sequence and the bacterial (Streptomyces lividans) K+-selective channel KcsA (Doyle et al., 1998; PDB record 1BL8A). Threading of the A. thaliana CNGC2 S6 transmembrane helix and pore region through the KcsA structure identifies the residues “AND” as in the ion conducting pathway where the residues “GYG” (shown in pink) that form the ion selectivity filter of a K+-selective channel are positioned. This suggests that plant CNGCs may have a mechanism for cation conductance that is conserved in P-loop channels. In plants, four separate CNGC peptides are presumed to form a tetrameric structure that shares the “inverted teepee” quaternary structure of animal P-loop channels.
Mentions: As indicated above, the quaternary structure of a member of the P-loop channel family is dependent on the assembly of four gene products in some cases (e.g., in animal and plant K+-selective voltage-gated channels) where only one P-loop “cassette” is encoded by the gene (i.e. S1–S6 with the P-loop between S5 and S6). It is therefore conceivable that plant CNGC channel complexes are formed by the assembly of four polypeptides, with each polypeptide corresponding to a structure similar to that shown in Figure 1B. Threading regions (S6 and pore loop, an example is shown in Figure 3 below) of plant CNGC coding sequences through the crystal structure of a quaternary P-loop channel indicates that the plant CNGC polypeptide may be capable of forming the tetrameric structure common to P-loop channels (Hua et al., 2003b). However, this model has not been verified experimentally. It should be noted that functional animal CNGC channel proteins are in all cases generated from such a tetrameric assembly of P-loop cassette polypeptides (Zheng and Zagotta, 2004) and that plant and animal CNGC polypeptides share a similar general S1–S6 topography. Thus, the aforementioned conjecture about the tetrameric structure of plant CNGCs is entirely consistent with the general concept of ion channel assembly and function.

Bottom Line: All eukaryote CNGC polypeptides have a cyclic nucleotide-binding domain and a calmodulin binding domain as well as a six transmembrane/one pore tertiary structure.Additionally, an amino acid motif that is only found in the phosphate binding cassette and hinge regions of plant CNGCs, and is present in all experimentally confirmed CNGCs but no other channels was identified.This CNGC-specific amino acid motif provides an additional diagnostic tool to identify plant CNGCs, and can increase confidence in the annotation of open reading frames in newly sequenced genomes as putative CNGCs.

View Article: PubMed Central - PubMed

Affiliation: Agricultural Biotechnology Laboratory, Department of Plant Science, University of Connecticut Storrs, CT, USA.

ABSTRACT
Ligand-gated cation channels are a frequent component of signaling cascades in eukaryotes. Eukaryotes contain numerous diverse gene families encoding ion channels, some of which are shared and some of which are unique to particular kingdoms. Among the many different types are cyclic nucleotide-gated channels (CNGCs). CNGCs are cation channels with varying degrees of ion conduction selectivity. They are implicated in numerous signaling pathways and permit diffusion of divalent and monovalent cations, including Ca(2+) and K(+). CNGCs are present in both plant and animal cells, typically in the plasma membrane; recent studies have also documented their presence in prokaryotes. All eukaryote CNGC polypeptides have a cyclic nucleotide-binding domain and a calmodulin binding domain as well as a six transmembrane/one pore tertiary structure. This review summarizes existing knowledge about the functional domains present in these cation-conducting channels, and considers the evidence indicating that plant and animal CNGCs evolved separately. Additionally, an amino acid motif that is only found in the phosphate binding cassette and hinge regions of plant CNGCs, and is present in all experimentally confirmed CNGCs but no other channels was identified. This CNGC-specific amino acid motif provides an additional diagnostic tool to identify plant CNGCs, and can increase confidence in the annotation of open reading frames in newly sequenced genomes as putative CNGCs. Conversely, the absence of the motif in some plant sequences currently identified as probable CNGCs may suggest that they are misannotated or protein fragments.

No MeSH data available.


Related in: MedlinePlus