Pattern formation of transcellular ionic currents in plant cells

Stationary and non-stationary spatio-temporal pattern formations are a common feature of biological cells and tissues. The propagation of an action potential along an excitable cell is a well-known example of non-stationary spatio-temporal pattern. Stationary patterns of ion concentration and electrical potential occur in plant cells and tissues. They are correlated to steady ionic currents through the cell membrane. For instance, in chara, a freshwater plant, periodic spatial variations of pH appear along the cylindrical internodal and whorl excitable cells (length from few millimetres to 15 cm) breaking the translation symmetry. The characteristic wavelength and time vary respectively from 1 mm to 2 cm and from 5 min to 60 min. This spatial pH pattern occurs upon activation of the plasma membrane H+-ATPase. In the absence of any external cue, the first pH band appears at a random position suggesting that the initial symmetric state is unstable. The cable model is widely used to understand spatio-temporal pattern formation in excitable cells. The success of this model rests on a typical feature of excitable cells: a negative differential conductance in part of the current-voltage characteristic of their membrane. It cannot explain stationary pattern formation of transcellular ionic current. We have used an electrodiffusive model coupled with cellular electric activity. We report here an unexpected property of the resulting model: a phase space domain that gives rise to stationary spatio-temporal patterns in the presence of a positive total differential membrane conductance. The model can explain stationary spatio-temporal pattern formation in both excitable and non-excitable cells. Our results indicate that these patterns occur if the H+-ATPase is coupled either to voltage-dependent ion channels or to a symport

Pattern formation by electrostatic self-organization of membrane proteins

International audienceThe electric activity of biological cells and organs such as heart for example is at the origin of various phenomena of pattern formation. The electric membrane potential appears as the order parameter to characterize these spatiotemporal dynamics. A kind of patterns is characterized by a stationary spatial modula- tion of membrane potential along the cell, breaking a symmetry of the system. They are associated to transcellular currents. A mechanism proposed in liter- ature is based on the coupling of the electric current produced by membrane proteins and their electrophoretic mobilities. Beyond its classical linear sta- bility analysis, the numerical and theoretical analysis of this model offers a variety of spatiotemporal dynamics. Firstly, the background in the modeliza- tion of electric phenomena is recalled. Secondly, the analysis is focused on two nonlinear dynamics

Regulation of the anion channel of the chloroplast envelope from spinach

International audienceSeveral anions such as Cl–, NO– 2, SO2– 4, and PO3– 4 are known to modulate the photosynthetic activity. Moreover, the chloroplast metabolism requires the exchange of both inorganic and organic (e.g., triose phosphate, dicarboxylic acid, ATP) anions between the cytoplasmand the stroma. A chloride channel form the chloroplast envelope was reconstituted in planar lipid bilayers. We show that the channel is active in conditions prevailing in the plant. The open probability increases with the ionic strength of the experimental solutions and is maximal at 0 mV. This suggests that the channel could play a role in the osmotic regulation of the chloroplast. Amino group reagents affect the channel activity in a way that demonstrated that lysine residues are important for channel gating but not for ATP binding. Together, our results provide new information on the functioning of this channel in the chloroplast envelope membranes. They indicate that the open probability of the channel is low (P o < 0.2) in vivo and that this channel can account for the chloride flux through the chloroplast envelope

Characterization of a porin channel in the endosymbiont of the trypanosomatid protozoan Crithidia deanei.

Crithidia deanei is a trypanosomatid protozoan that harbours a symbiotic bacterium. The partners maintain a mutualistic relationship, thus constituting an excellent model for studying metabolic exchanges between the host and the symbiont, the origin of organelles and cellular evolution. According to molecular analysis, symbionts of different trypanosomatid species share high identity and descend from a common ancestor, a β-proteobacterium of the genus Bordetella. The endosymbiont is surrounded by two membranes, like Gram-negative bacteria, but its envelope presents special features, since phosphatidylcholine is a major membrane component and the peptidoglycan layer is highly reduced, as described in other obligate intracellular bacteria. Like the process that generated mitochondria and plastids, the endosymbiosis in trypanosomatids depends on pathways that facilitate the intensive metabolic exchanges between the bacterium and the host protozoan. A search of the annotated symbiont genome database identified one sequence with identity to porin-encoding genes of the genus Bordetella. Considering that the symbiont outer membrane has a great accessibility to cytoplasm host factors, it was important to characterize this single porin-like protein using biochemical, molecular, computational and ultrastructural approaches. Antiserum against the recombinant porin-like molecule revealed that it is mainly located in the symbiont envelope. Secondary structure analysis and comparative modelling predicted the protein 3D structure as an 18-domain β-barrel, which is consistent with porin channels. Electrophysiological measurements showed that the porin displays a slight preference for cations over anions. Taken together, the data presented herein suggest that the C. deanei endosymbiont porin is phylogenetically and structurally similar to those described in Gram-negative bacteria, representing a diffusion channel that might contribute to the exchange of nutrients and metabolic precursors between the symbiont and its host cell.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

APOL1 C-Terminal Variants May Trigger Kidney Disease through Interference with APOL3 Control of Actomyosin

The C-terminal variants G1 and G2 of apolipoprotein L1 (APOL1) confer human resistance to the sleeping sickness parasite Trypanosoma rhodesiense, but they also increase the risk of kidney disease. APOL1 and APOL3 are death-promoting proteins that are partially associated with the endoplasmic reticulum and Golgi membranes. We report that in podocytes, either APOL1 C-terminal helix truncation (APOL1Δ) or APOL3 deletion (APOL3KO) induces similar actomyosin reorganization linked to the inhibition of phosphatidylinositol-4-phosphate [PI(4)P] synthesis by the Golgi PI(4)-kinase IIIB (PI4KB). Both APOL1 and APOL3 can form K+ channels, but only APOL3 exhibits Ca2+-dependent binding of high affinity to neuronal calcium sensor-1 (NCS-1), promoting NCS-1-PI4KB interaction and stimulating PI4KB activity. Alteration of the APOL1 C-terminal helix triggers APOL1 unfolding and increased binding to APOL3, affecting APOL3-NCS-1 interaction. Since the podocytes of G1 and G2 patients exhibit an APOL1Δ or APOL3KO-like phenotype, APOL1 C-terminal variants may induce kidney disease by preventing APOL3 from activating PI4KB, with consecutive actomyosin reorganization of podocytes.status: publishe