This document discusses aquaporins, which are membrane channel proteins that facilitate the efficient transport of water across cell membranes. It outlines the key structural features of aquaporins, including their six transmembrane helices and hourglass shape. The document also notes that aquaporins are found across life forms and help transport water in critical biological functions like plant water transport and bacterial water movement. Finally, it briefly discusses some human aquaporins and their roles in diseases like nephrogenic diabetes insipidus.
2. OutlineOutline
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What is an Aquaporin?
Specie Distribution
Structural Features
Mechanism of Action
Human Aquaporins
Medical Aspects of AQPs
Conclusion
3. Major Intrinsic Proteins (MIPs)Major Intrinsic Proteins (MIPs)
Transmembrane
protein family
High sequence
similarity
Two types of channels:
1) Aquaporins
2) Glycerol Facilitators
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4. What is an Aquaporin?What is an Aquaporin?
Six transmembrane helices joined together
Found in all life forms
Allow efficient permeation of water
High specificity for water
Highly conserved
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7. Species DistributionSpecies Distribution
13 known types in Mammals
GlpF and AQPZ in E.coli
5 subfamilies in Plants (PIP,TIP, NIP, XIP, SIP)
Human AQPs – 10 different genes
Aquaporin family: (AQPs) and (AQGPs)
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9. Structural Features of AquaporinsStructural Features of Aquaporins
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Six transmembrane helices
C and N terminals
Extracellular loop A, C and E
Intracellular loop B and D
Highly conserved NPA motif
11. Hourglass FoldHourglass Fold
Loop B and E fold into membrane and
form Hourglass Fold
Wide external openings to the channel
with a narrow central constriction
form the functional water pore
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13. Ar/R Selectivity FilterAr/R Selectivity Filter
Cluster of amino acids help bind to water
Prevent other molecules to enter
membrane
Tetrad:Two residues from helices 2 (H2)
and 5 (H5) and two residues from loop E
(LE1) and (LE2)
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14. Role of AquaporinsRole of Aquaporins
Increase rate of water transport
Prevent other molecules to enter in
membrane
Symplastic movement of water in plants
Water transport in prokaryotes (AQPZ)
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15. Mechanism of ActionMechanism of Action
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Water molecules orient themselves as
Single-File H bonded chain
Water interacts with NPA and rotated at
180˚
Fast flux is maintained
Low Activation energy needed