Abstract
Plant NHX antiporters are responsible for monovalent cation/H+ exchange across cellular membranes and play therefore a critical role for cellular pH regulation, Na+ and K+ homeostasis, and salt tolerance. Six members of grapevine NHX family (VvNHX1-6) have been structurally characterized. Phylogenetic analysis revealed their organization in two groups: VvNHX1-5 belonging to group I (vacuolar) and VvNHX6 belonging to group II (endosomal). Conserved domain analysis of these VvNHXs indicates the presence of different kinds of domains. Out of these, two domains function as monovalent cation-proton antiporters and one as the aspartate-alanine exchange; the remaining are not yet with defined function. Overall, VvNHXs proteins are typically made of 11-13 putative transmembrane regions at their N-terminus which contain the consensus amiloride-binding domain in the 3rd TM domain and a cation-binding site in between the 5th and 6th TM domain, followed by a hydrophilic C-terminus that is the target of several and diverse regulatory posttranslational modifications. Using a combination of primary structure analysis, secondary structure alignments, and the tertiary structural models, the VvNHXs revealed mainly 18 α helices although without β sheets. Homology modeling of the 3D structure showed that VvNHX antiporters are similar to the bacterial sodium proton antiporters MjNhaP1 (Methanocaldococcus jannaschii) and PaNhaP (Pyrococcus abyssi).
Highlights
The NHX antiporters family mediates cation/proton exchange across different cellular membranes, using electrochemical gradients generated by proton translocating enzymes, namely, H+-ATPase in the plasma membrane and vacuolar ATPase and pyrophosphatase within the intracellular compartments [1, 2]
Six members of grapevine NHX family (VvNHX16) have been structurally characterized. Phylogenetic analysis revealed their organization in two groups: VvNHX1-5 belonging to group I and VvNHX6 belonging to group II
Homology modeling of the 3D structure showed that VvNHX antiporters are similar to the bacterial sodium proton antiporters MjNhaP1 (Methanocaldococcus jannaschii) and PaNhaP (Pyrococcus abyssi)
Summary
The NHX antiporters family mediates cation/proton exchange across different cellular membranes, using electrochemical gradients generated by proton translocating enzymes, namely, H+-ATPase in the plasma membrane and vacuolar ATPase and pyrophosphatase within the intracellular compartments [1, 2] Members of this NHX family are found in all living organisms and cells, from prokaryotic to eukaryotic. Several computer tools and programs for structure prediction have been developed and are available [6] In this context, our work focuses on structural features determination of grapevine NHX antiporters via the use of computational and in silico methods. The objective of our study is to predict the BioMed Research International three-dimensional structure of Vitis vinifera NHX antiporter protein family through homology modeling and examine its physicochemical properties using in silico approaches. The homology model was developed using different software packages and the best model was selected upon evaluation
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