AQP8 Membrane Protein Introduction

Introduction of AQP8

AQP8 is a transmembrane channel that in humans is encoded by the AQP8 gene. AQP8 protein is predicted to consist of 261-amino acid and contains 6 membrane-spanning domains, 2 highly conserved asn-pro-ala (NPA) motifs, and 3 N-linked glycosylation sites. AQP8 is expressed in pancreas and colon, especially on the apical and basolateral membranes of cholangiocytes. In mice, AQP8 is also detected in the plasma membranes of hepatocytes. AQP8 facilitates water permeability through cell membranes and is essential for the regulation of water homeostasis.

Basic Information of AQP8
Protein Name	Aquaporin-8
Gene Name	AQP8
Aliases	None
Organism	Homo sapiens (Human)
UniProt ID	O94778
Transmembrane Times	6
Length (aa)	261
Sequence	MSGEIAMCEPEFGNDKAREPSVGGRWRVSWYERFVQPCLVELLGSALFIFIGCLSVIENGTDTGLLQPALAHGLALGLVIATLGNISGGHFNPAVSLAAMLIGGLNLVMLLPYWVSQLLGGMLGAALAKAVSPEERFWNASGAAFVTVQEQGQVAGALVAEIILTTLLALAVCMGAINEKTKGPLAPFSIGFAVTVDILAGGPVSGGCMNPARAFGPAVVANHWNFHWIYWLGPLLAGLLVGLLIRCFIGDGKTRLILKAR

Function of AQP8 Membrane Protein

The most well-known function of AQP8 is to conduct water, ammonia, urea, glycerol and H₂O₂ through various membranes of animal cells. In addition, AQP8 has been connected to a number of phenomena, such as volume change of mitochondria, ammonia neurotoxicity, and mitochondrial dysfunction related to oxidative stress. It is documented that AQP8 is associated with multiple tumors, such as breast cancer, lung cancer, prostatic carcinoma and colorectal cancer, and AQP8 over-expression can remarkably decrease the growth and aggressiveness of the tumor and inhibit tumorigenic phenotype by inactivating PI3K/AKT signaling pathway. It is documented that upregulation of AQP8 could contribute to the development of hepatocellular swelling after hepatic Ischemia-reperfusion (IR) injury. AQP8 is reported to transport ammonium in vivo and physiologically contribute to the acid-base equilibrium.

Fig.1 Molecular modeling of AQP8. (Bestetti, 2018)

Application of AQP8 Membrane Protein in Literature

Bestetti S., et al. A persulfidation-based mechanism controls aquaporin-8 conductance. Sci Adv. 2018, 4: eaar5770. PubMed ID: 29732408

The authors demonstrate that AQP8 gating is mediated by persulfidation of cysteine 53 and H₂O₂ is transported through AQP8 sulfenylate C53, making it susceptible to H₂S produced by cystathionine β-synthase (CBS).
Wu Q., et al. AQP8 inhibits colorectal cancer growth and metastasis by down-regulating PI3K/AKT signaling and PCDH7 expression. Am J Cancer Res. 2018, 8: 266-279. PubMed ID: 29511597

The study verifies the vital role of the endogenous AQP8 in colorectal cancer cells growth and metastasis. Over-expression of AQP8 can remarkably decrease growth, aggressiveness and colony formation in colorectal cancer cells.
Kirscht A., et al. A structural preview of aquaporin 8 via homology modeling of seven vertebrate isoforms. BMC Struct Biol. 2018, 18: 2. PubMed ID: 29454339

The authors present homology models of seven vertebrate AQP8s and the key amino acids are predicted. They demonstrate that AQP8s are likely to have an AtTIP2;1-like selectivity filter and verify the correctness of the model by a series of experiments.
Danielli M., et al. Cholesterol can modulate mitochondrial aquaporin-8 expression in human hepatic cells. IUBMB Life. 2017, 69: 341-346. PubMed ID: 28322010

This article suggests that cholesterol can regulate transcriptionally mitochondrial aquaporin-8 (mtAQP8) expression in human hepatic cells, and this process is realized by sterol regulatory element-binding protein (SREBP).

AQP8 Preparation Options

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Reference

Bestetti S, et al. (2018). A persulfidation-based mechanism controls aquaporin-8 conductance. Sci Adv. 4, eaar5770.

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