Aquaporins - Expression, purification and characterization

The Important Role of Aquaglyceroporin 7 in Health and Disease

Aquaporins (AQPs) are highly conserved small transmembrane proteins that facilitate the transport of water and small solutes across cell membranes. Aquaglyceroporin 7 (AQP7), a significant member of the AQP family, is widely distributed throughout the body. For years, AQP7 was predominantly recognized for its role as a small-molecule transporter, facilitating the passage of small molecular substances. However, growing studies have revealed that AQP7 is also involved in the regulation of lipid synthesis, gluconeogenesis, and energy homeostasis, and it is intimately linked to a variety of diseases, such as obesity, type 2 diabetes mellitus, cardiovascular diseases, cancer, and inflammatory bowel disease. This article presents a comprehensive overview of the structure of AQP7, its regulatory mechanisms, its vital roles in both healthy and diseased states, and potential therapeutic advancements. We hope that these studies will serve as a valuable reference for the development of future treatments and diagnostic protocols targeting AQP7.

Alpinetin alleviates LPS-induced lung epithelial cell injury by inhibiting p38 and ERK1/2 signaling via aquaporin-1

Alpinetin has been reported to play a protective role in lung diseases, while its special mechanisms remain indistinct. In this study, acute lung injury (ALI) model was constructed by inducing MLE-12 cells with lipopolysaccharide (LPS). Cell activity together with apoptosis was judged employing cell counting kit-8 (CCK-8), flow cytometry along with western blot. Oxidative stress levels were measured by dichloro-dihydro-fluorescein diacetate (DCFH-DA) staining and corresponding kits. In addition, enzyme-linked immunosorbent assay (ELISA) was to examine the levels of inflammatory factors. The protein expressions of aquaporin-1 (AQP1), p38 and extracellular signal-regulated kinase (ERK) 1/2 pathway were estimated utilizing western blot. The data showed that alpinetin increased the viability, reduced the apoptosis, oxidative stress and inflammation and inactivated p38 and ERK1/2 signaling in LPS-induced MLE-12 cells. Moreover, alpinetin also increased AQP1 expression and AQP1 knockdown reversed the impacts of alpinetin on LPS-induced MLE-12 cells. Additionally, AQP1 agonist AqF026 also exerted anti-apoptotic and anti-inflammatory activities in LPS-treated MLE-12 cells. Evidently, alpinetin may exert its protective role in LPS-induced ALI by inactivation of p38 and ERK1/2 signaling through regulating AQP1.

Microbial membrane transport proteins and their biotechnological applications

Because of the hydrophobic nature of the membrane lipid bilayer, the majority of the hydrophilic solutes require special transportation mechanisms for passing through the cell membrane. Integral membrane transport proteins (MTPs), which belong to the Major Intrinsic Protein Family, facilitate the transport of these solutes across cell membranes. MTPs including aquaporins and carrier proteins are transmembrane proteins spanning across the cell membrane. The easy handling of microorganisms enabled the discovery of a remarkable number of transport proteins specific to different substances. It has been realized that these transporters have very important roles in the survival of microorganisms, their pathogenesis, and antimicrobial resistance. Astonishing features related to the solute specificity of these proteins have led to the acceleration of the research on the discovery of their properties and the development of innovative products in which these unique properties are used or imitated. Studies on microbial MTPs range from the discovery and characterization of a novel transporter protein to the mining and screening of them in a large transporter library for particular functions, from simulations and modeling of specific transporters to the preparation of biomimetic synthetic materials for different purposes such as biosensors or filtration membranes. This review presents recent discoveries on microbial membrane transport proteins and focuses especially on formate nitrite transport proteins and aquaporins, and advances in their biotechnological applications.

Toward New AQP4 Inhibitors: ORI-TRN-002

Cerebral edema is a life-threatening condition that can cause permanent brain damage or death if left untreated. Existing therapies aim at mitigating the associated elevated intracranial pressure, yet they primarily alleviate pressure rather than prevent edema formation. Prophylactic anti-edema therapy necessitates novel drugs targeting edema formation. Aquaporin 4 (AQP4), an abundantly expressed water pore in mammalian glia and ependymal cells, has been proposed to be involved in cerebral edema formation. A series of novel compounds have been tested for their potential inhibitory effects on AQP4. However, selectivity, toxicity, functional inhibition, sustained therapeutic concentration, and delivery into the central nervous system are major challenges. Employing extensive density-functional theory (DFT) calculations, we identified a previously unreported thermodynamically stable tautomer of the recently identified AQP4-specific inhibitor TGN-020 (2-(nicotinamide)-1,3,4-thiadiazol). This novel form, featuring a distinct hydrogen-bonding pattern, served as a template for a COSMOsim-3D-based virtual screen of proprietary compounds from Origenis™. The screening identified ORI-TRN-002, an electronic homologue of TGN-020, demonstrating high solubility and low protein binding. Evaluating ORI-TRN-002 on AQP4-expressing Xenopus laevis oocytes using a high-resolution volume recording system revealed an IC50 of 2.9 ± 0.6 µM, establishing it as a novel AQP4 inhibitor. ORI-TRN-002 exhibits superior solubility and overcomes free fraction limitations compared to other reported AQP4 inhibitors, suggesting its potential as a promising anti-edema therapy for treating cerebral edema in the future.

Genome-Wide Identification and Expression Pattern Profiling of the Aquaporin Gene Family in Papaya (Carica papaya L.)

Aquaporins (AQPs) are mainly responsible for the transportation of water and other small molecules such as CO2 and H2O2, and they perform diverse functions in plant growth, in development, and under stress conditions. They are also active participants in cell signal transduction in plants. However, little is known about AQP diversity, biological functions, and protein characteristics in papaya. To better understand the structure and function of CpAQPs in papaya, a total of 29 CpAQPs were identified and classified into five subfamilies. Analysis of gene structure and conserved motifs revealed that CpAQPs exhibited a degree of conservation, with some differentiation among subfamilies. The predicted interaction network showed that the PIP subfamily had the strongest protein interactions within the subfamily, while the SIP subfamily showed extensive interaction with members of the PIP, TIP, NIP, and XIP subfamilies. Furthermore, the analysis of CpAQPs' promoters revealed a large number of cis-elements participating in light, hormone, and stress responses. CpAQPs exhibited different expression patterns in various tissues and under different stress conditions. Collectively, these results provided a foundation for further functional investigations of CpAQPs in ripening, as well as leaf, flower, fruit, and seed development. They also shed light on the potential roles of CpAQP genes in response to environmental factors, offering valuable insights into their biological functions in papaya.

Cloning and Overexpressing Membrane Proteins Using Pichia pastoris (Komagataella phaffii)

Understanding the structure and function of key proteins located within biological membranes is essential for fundamental knowledge and therapeutic applications. Robust cell systems allowing their actual overexpression are required, among which stands the methylotrophic yeast Pichia pastoris. This system proves highly efficient in producing many eukaryotic membrane proteins of various functions and structures at levels and quality compatible with their subsequent isolation and molecular investigation. This article describes a set of basic guidelines and directions to clone and select recombinant P. pastoris clones overexpressing eukaryotic membrane proteins. Illustrative results obtained for a panel of mammalian membrane proteins are presented, and hints are given on a series of experimental parameters that may substantially improve the amount and/or the functionality of the expressed proteins. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Designing and cloning a P. pastoris expression vector Basic Protocol 2: Integrative transformation of P. pastoris and selection of recombinant clones Basic Protocol 3: Culturing transformed P. pastoris for membrane protein expression Basic Protocol 4: Yeast cell lysis and membrane preparation Basic Protocol 5: Immunodetection of expressed membrane proteins: western blot Alternate Protocol 1: Immunodetection of expressed membrane proteins: dot blot Alternate Protocol 2: Immunodetection of expressed membrane proteins: yeastern blot Basic Protocol 6: Activity assay: ligand-binding analysis of an expressed GPCR.

1Progress, applications, challenges and prospects of protein purification technology

Protein is one of the most important biological macromolecules in life, which plays a vital role in cell growth, development, movement, heredity, reproduction and other life activities. High quality isolation and purification is an essential step in the study of the structure and function of target proteins. Therefore, the development of protein purification technologies has great theoretical and practical significance in exploring the laws of life activities and guiding production practice. Up to now, there is no forthcoming method to extract any proteins from a complex system, and the field of protein purification still faces significant opportunities and challenges. Conventional protein purification generally includes three steps: pretreatment, rough fractionation, and fine fractionation. Each of the steps will significantly affect the purity, yield and the activity of target proteins. The present review focuses on the principle and process of protein purification, recent advances, and the applications of these technologies in the life and health industry as well as their far-reaching impact, so as to promote the research of protein structure and function, drug development and precision medicine, and bring new insights to researchers in related fields.

Aquaporins: Important players in the cardiovascular pathophysiology

Aquaporin is a membrane channel protein widely expressed in body tissues, which can control the input and output of water in cells. AQPs are differentially expressed in different cardiovascular tissues and participate in water transmembrane transport, cell migration, metabolism, inflammatory response, etc. The aberrant expression of AQPs highly correlates with the onset of ischemic heart disease, myocardial ischemia-reperfusion injury, heart failure, etc. Despite much attention to the regulatory role of AQPs in the cardiovascular system, the translation of AQPs into clinical application still faces many challenges, including clarification of the localization of AQPs in the cardiovascular system and mechanisms mediating cardiovascular pathophysiology, as well as the development of cardiovascular-specific AQPs modulators.Therefore, in this study, we comprehensively reviewed the critical roles of AQP family proteins in maintaining cardiovascular homeostasis and described the underlying mechanisms by which AQPs mediated the outcomes of cardiovascular diseases. Meanwhile, AQPs serve as important therapeutic targets, which provide a wide range of opportunities to investigate the mechanisms of cardiovascular diseases and the treatment of those diseases.

RhRab5ip, a new interactor of RhPIP1;1, was involved in flower opening of cut rose during water deficit

Flower opening is a process primarily caused by water uptake-driven petal cell expansion. while which is easily affected by water deficit during transportation of cut flowers, resulting in abnormal flower opening. The knowledge of important players during this process remains limited. We previously reported that the aquaporin RhPIP1;1 plays an important role in ethylene-regulated petal cell expansion in rose flower. Here, we identified RhRab5ip as a new interactor of RhPIP1;1. RhRab5ip belongs to the Rab5-interacting protein (Rab5ip) family and may function in vesicle trafficking pathway. By using split ubiquitin yeast two-hybrid (SUY2H) system, bimolecular fluorescence complementation (BiFC) and subcellular colocalization we confirmed the existence of physical interaction between RhPIP1;1 and RhRab5ip in yeast and plant cell. The interaction of these two proteins happened at the small punctate structures in the cytoplasm. Expression of RhRab5ip in petals increased substantially at the initial stage of flower opening and maintained at high level until flower wilting. The transcripts of both RhRab5ip and RhPIP1;1 were greatly up-regulated by ABA and GA₃ treatments, while only RhPIP1;1 was down-regulated by ethylene. Moreover, both RhRab5ip and RhPIP1;1 were significantly induced by water deficit treatment after 12 h-treatment, when flowers started to wilt and showed neck bending. Taken together, these findings suggested that RhRab5ip might functionally coordinate with RhPIP1;1 in response to water deficit stress in rose flower, expanding our understanding of the possible involvement of Rab5ip protein in the regulatory network of flower opening during water deficit.

Aquaporin-3 and Aquaporin-5 Facilitate Migration and Cell-Cell Adhesion in Pancreatic Cancer by Modulating Cell Biomechanical Properties

BACKGROUND

Aquaporins are membrane channels responsible for the bidirectional transfer of water and small non-charged solutes across cell membranes. AQP3 and AQP5 are overexpressed in pancreatic ductal adenocarcinoma, playing key roles in cell migration, proliferation, and invasion. Here, we evaluated AQP3 and AQP5 involvement in cell biomechanical properties, cell-cell adhesion, and cell migration, following a loss-of-function strategy on BxPC-3 cells.

RESULTS

Silencing of AQP3 and AQP5 was functionally validated by reduced membrane permeability and had implications on cell migration, slowing wound recovery. Moreover, silenced AQP5 and AQP3/5 cells showed higher membrane fluidity. Biomechanical and morphological changes were assessed by atomic force microscopy (AFM), revealing AQP5 and AQP3/5 silenced cells with a lower stiffness than their control. Through cell-cell adhesion measurements, the work (energy) necessary to detach two cells was found to be lower for AQP-silenced cells than control, showing that these AQPs have implications on cell-cell adhesion.

CONCLUSION

These findings highlight AQP3 and AQP5 involvement in the biophysical properties of cell membranes, whole cell biomechanical properties, and cell-cell adhesion, thus having potential implication in the settings of tumor development.

Beyond the Channels: Adhesion Functions of Aquaporin 0 and Connexin 50 in Lens Development

Lens, an avascular tissue involved in light transmission, generates an internal microcirculatory system to promote ion and fluid circulation, thus providing nutrients to internal lens cells and excreting the waste. This unique system makes up for the lack of vasculature and distinctively maintains lens homeostasis and lens fiber cell survival through channels of connexins and other transporters. Aquaporins (AQP) and connexins (Cx) comprise the majority of channels in the lens microcirculation system and are, thus, essential for lens development and transparency. Mutations of AQPs and Cxs result in abnormal channel function and cataract formation. Interestingly, in the last decade or so, increasing evidence has emerged suggesting that in addition to their well-established channel functions, AQP0 and Cx50 play pivotal roles through channel-independent actions in lens development and transparency. Specifically, AQP0 and Cx50 have been shown to have a unique cell adhesion function that mediates lens development and transparency. Precise regulation of cell-matrix and cell-cell adhesion is necessary for cell migration, a critical process during lens development. This review will provide recent advances in basic research of cell adhesion mediated by AQP0 and Cx50.

Recent breakthroughs and future directions in drugging aquaporins

Aquaporins facilitate the passive transport of water, solutes, or ions across biological membranes. They are implicated in diverse pathologies including brain edema following stroke or trauma, epilepsy, cancer cell migration and tumor angiogenesis, metabolic disorders, and inflammation. Despite this, there is no aquaporin-targeted drug in the clinic and aquaporins have been perceived to be intrinsically non-druggable targets. Here we challenge this idea, as viable routes to inhibition of aquaporin function have recently been identified, including targeting their regulation or their roles as channels for unexpected substrates. Identifying new drug development frameworks for conditions associated with disrupted water and solute homeostasis will meet the urgent, unmet clinical need of millions of patients for whom no pharmacological interventions are available.