The structure of aquaporins

Abstract

1. Introduction 3621.1 The elusive water pores 3621.2 CHIP28 3622. Studies on AQP-1 3632.1 Expression of AQP1 cDNA in Xenopus oocytes 3632.2 Reconstitution of purified AQP1 into artificial lipid bilayers 3642.3 Structural information deduced from the primary sequence 3652.4 Evolution and mammalian AQPs 3653. Chronological overview over AQP structures 3683.1 AQP1 – the red blood cell water pore 3683.2 GlpF – the E. coli glycerol facilitator 3713.3 AQPZ – the E. coli water pore 3723.4 AQP0 – the lens-specific aquaporin 3733.5 AQP4 – the main aquaporin in brain 3773.6 SoPiP2;1 – a plant aquaporin 3793.7 AQPM – an archaeabacterial aquaporin 3794. Proton exclusion 3805. Substrate selectivity 3826. Pore regulation 3856.1 Hormonal regulation of AQP trafficking 3856.2 Influence of pH on AQP water conduction 3866.3 Regulation of AQP pore conductance by protein binding 3876.4 Pore closure by conformational changes in the AQP0 pore 3887. Unresolved questions 3908. Acknowledgments 3909. References 391The ubiquitous members of the aquaporin (AQP) family form transmembrane pores that are either exclusive for water (aquaporins) or are also permeable for other small neutral solutes such as glycerol (aquaglyceroporins). The purpose of this review is to provide an overview of our current knowledge of AQP structures and to describe the structural features that define the function of these membrane pores. The review will discuss the mechanisms governing water conduction, proton exclusion and substrate specificity, and how the pore permeability is regulated in different members of the AQP family.