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.

1. The Aquaporin WaterThe Aquaporin Water
ChannelsChannels

2. OutlineOutline
2
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
3

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
4

5. 5

6. DiscoveryDiscovery
Isolated from RBCs by Peter Agre in1992
Termed as Aquaporins
6

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)
7

8. Bacterial AquaporinsBacterial Aquaporins
Trp,Arg,Phe form
constriction
Two classes of
bacterial AQP
◦ AQPZ : An explicit
water channel
◦ GlpF : Transport
glycerol
8

9. Structural Features of AquaporinsStructural Features of Aquaporins
9
Six transmembrane helices
C and N terminals
Extracellular loop A, C and E
Intracellular loop B and D
Highly conserved NPA motif

10. The NPA MotifThe NPA Motif
10
Asp-Pro-Ala
Highly conserved
amino acid 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
11

12. 12

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)
13

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)
14

15. Mechanism of ActionMechanism of Action
15
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

16. 16

17. Human AquaporinsHuman Aquaporins
17

18. Aquaporins and DiseaseAquaporins and Disease
AQP-2 gene: Hereditary Nephrogenic
Diabetes Insipidus
AQP-4 gene: Devic's Disease
AQP-0 gene: Congenital Cataracts in mice
18

19. ConclusionConclusion
AQPs are:
• Highly conserved
• Of Supreme importance
• Plumbing system of cell
19

20. Future InsightsFuture Insights
Much to learn yet…
Design therapeutic models
More technology and research work
needed
20

21. ReferencesReferences
 http://www.aquaporins.org/
 http://www.wikidoc.org/index.php/Aquaporin_1
 http://en.allexperts.com/e/a/aq/aquaporin.htm
 http://www.pharmainfo.net/reviews/aquaporins-secret-highways-water-
transport
 http://www.danfoss-aquaz.com/aquaporins.asp
 http://www.bio.miami.edu/~cmallery/150/memb/water.channels.htm
21