Slide 1 : PLANT AQUAPORINS Presented By:Shikha Sinha AQUAPORINS REGULATION OF AQUAPORIN ACTIVITY
Discovery Of Aquaporin : Discovery Of Aquaporin
AQUAPORIN : AQUAPORIN These channels are widely distributed in all kingdoms of life, including bacteria, plants, and mammals.
In human more than 10 aquaporins and in plant more than 30 aquaporins. Aquaporins are membrane water channels that play critical roles in controlling the water contents of cells.They are present in both plasma and vacuolar membrane.
Homologous Subfamilies : Homologous Subfamilies Small basic intrinsic protein(SIP).
Nodulin-26 like intrinsic protein(NIP).
Tonoplast intrinsic protein(TIP).
Plasma Intrinsic membrane protein(PIP).
AQUAPORIN : AQUAPORIN A class of major intrinsic proteins (MIP). Highly selective and efficient water channels(109/s).
Slide 6 : Aquaporin channel homo-tetramer monomer
Slide 7 :
Water transport through Aquaporins : Water transport through Aquaporins Molecular dynamics computer simulation of the transport of water through a cell membrane protein aquaporin.
- About 100 000 atoms
- Simulation time 5 ns
- Lipid bilayer not shown
Watch the trajectory of the
water molecule highlighted
in yellow:
Slide 9 : The water pores are completely impermeable to charged species, such as protons, a remarkable property that is critical for the conservation of membrane's electrochemical potential. Water molecules passing the channel are forced, by the protein's electrostatic forces, to flip at the center of the channel thereby breaking the alternative donor-acceptor arrangement that is necessary for proton translocation.
REGULATION OF PLANT AQUAPORIN ACTIVITY : REGULATION OF PLANT AQUAPORIN ACTIVITY Reversible Phosphorylation
pH and pCa
Heteromerisation
Oxidative stress
Osmotic and hydrostatic pressure
Membrane Trafficking
Sensitivity to heavy metal ions
Selectivity of plant aquaporin
REVERSIBLE PHOSPHORYLATION : REVERSIBLE PHOSPHORYLATION Aquaporin are regulated by a block or shift from an activated to an inactivated state.It suggest as a molecular mechanism for the transition.
Slide 12 : pH and ca2+ pH sensitivity depends on position of Histidine on loop D in PIPs. Ca2+ and other divalent ion in range of 10-100 microM down regulate water channels.
HETERO-TETRAMER FORMATION : HETERO-TETRAMER FORMATION The aquaporin of PIP1 and PIP2 subgroup function in co-operative manner to determine plant plasma membrane water permeability.
OSMOTIC AND HYDROSTATIC PRESSURE : OSMOTIC AND HYDROSTATIC PRESSURE Water channel inhibition increases with increasing concentration and size of osmolyte.
Pressure pulses of varying amplitude differentially alters the hydraulic conductivity.
MEMBRANE TRAFFICKING : MEMBRANE TRAFFICKING Osmotic stress induces a shift in localization from tonoplast to higher density fraction. Pressure pulses of varying amplitude differentially alters the hydraulic conductivity.
Sensitivity to heavy metal ions-mercury Compounds interact with a mechanism Leading to active sequestering of water
SELECTIVITY OF PLANT AQUAPORIN : SELECTIVITY OF PLANT AQUAPORIN Human AQP3-glycerol and urea
AQP1-CO2
NOD26-glycerol
Slide 17 : TOWARDS AN INTEGRATED VIEW OF AQUAPORIN REGULATION IN ROOTS ? 1.Gating of aquaporin through different mechanism represent a rapid pathway of response to environmental constraints such as anoxia, salt and water stress.
2.Reduced water uptake under salt exposure prevent mass flow of salt towards aerial part
3.Under anoxia, down regulation of water uptake prevent sudden dilution xylem sap.
4.Reduced water uptake from soil contaminated by salt or colonized microbe prevent drag of toxic salt or microbial toxin
5.Enhanced water uptake in nutrient rich area promote diffusion of nutrient to root vicinity.
Slide 18 : Aquaporin regulation do not function individually. water stress acts on aquaporin function at the level of transcription, protein relocalization, and gating through reversible phosphorylation or direct effects of osmotic or hydrostatic gradient.
A challenge for future research will be to understand how plants integrate these mechanisms in time and space, to constantly adjust the water transport and solute transport properties of their membranes.
Example:
Antisense inhibition of PIP aquaporins in tobacco and Arabidopsis resulted in a marked defect in the plants ability torecover from water stress.
Over-expression of RWC3 in a drought-sensitive cultivar, under the control of a stress inducible promoter, was able to improve the growth per-formance. CONCLUSION AND FUTURE PERSPECTIVES
Slide 19 :