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Contains fulltext : 283350.pdf (Publisher’s version ) (Closed access), Magnesium (Mg(2+)) is the most prevalent divalent intracellular cation. As co-factor in many enzymatic reactions, Mg(2+) is essential for protein synthesis, energy production, and DNA stability. Disturbances in intracellular Mg(2+) concentrations, therefore, unequivocally result in delayed cell growth and metabolic defects. To maintain physiological Mg(2+) levels, all organisms rely on balanced Mg(2+) influx and efflux via Mg(2+) channels and transporters. This review compares the structure and the function of prokaryotic Mg(2+) transporters and their eukaryotic counterparts. In prokaryotes, cellular Mg(2+) homeostasis is orchestrated via the CorA, MgtA/B, MgtE, and CorB/C Mg(2+) transporters. For CorA, MgtE, and CorB/C, the motifs that form the selectivity pore are conserved during evolution. These findings suggest that CNNM proteins, the vertebrate orthologues of CorB/C, also have Mg(2+) transport capacity. Whereas CorA and CorB/C proteins share the gross quaternary structure and functional properties with their respective orthologues, the MgtE channel only shares the selectivity pore with SLC41 Na(+)/Mg(2+) transporters. In eukaryotes, TRPM6 and TRPM7 Mg(2+) channels provide an additional Mg(2+) transport mechanism, consisting of a fusion of channel with a kinase. The unique features these TRP channels allow the integration of hormonal, cellular, and transcriptional regulatory pathways that determine their Mg(2+) transport capacity. Our review demonstrates that understanding the structure and function of prokaryotic magnesiotropic proteins aids in our basic understanding of Mg(2+) transport.

Radboud University, 05 oktober 2022, Promotor : Bindels, R.J.M. Co-promotor : Baaij, J.H.F. de, Contains fulltext : 281783.pdf (Publisher’s version ) (Closed access)

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01 juli 2021, Item does not contain fulltext, Cyclin M (CNNM1-4) proteins maintain cellular and body magnesium (Mg(2+)) homeostasis. Using various biochemical approaches, we have identified members of the CNNM family as direct interacting partners of ADP-ribosylation factor-like GTPase 15 (ARL15), a small GTP-binding protein. ARL15 interacts with CNNMs at their carboxyl-terminal conserved cystathionine-β-synthase (CBS) domains. In silico modeling of the interaction between CNNM2 and ARL15 supports that the small GTPase specifically binds the CBS1 and CNBH domains. Immunocytochemical experiments demonstrate that CNNM2 and ARL15 co-localize in the kidney, with both proteins showing subcellular localization in the endoplasmic reticulum, Golgi apparatus and the plasma membrane. Most importantly, we found that ARL15 is required for forming complex N-glycosylation of CNNMs. Overexpression of ARL15 promotes complex N-glycosylation of CNNM3. Mg(2+) uptake experiments with a stable isotope demonstrate that there is a significant increase of (25)Mg(2+) uptake upon knockdown of ARL15 in multiple kidney cancer cell lines. Altogether, our results establish ARL15 as a novel negative regulator of Mg(2+) transport by promoting the complex N-glycosylation of CNNMs.

Item does not contain fulltext, Neurological disorders, including seizures, migraine, depression, and intellectual disability, are frequently associated with hypomagnesemia. Specifically, magnesium (Mg2+) channel transient receptor potential melastatin (TRPM) 6 and TRPM7 are essential for brain function and development. Both channels are also localized in renal and intestinal epithelia and are crucial for Mg2+(re)absorption. Cyclin M2 (CNNM2) is located on the basolateral side of the distal convoluted tubule. In addition, it plays a role in the maintenance of plasma Mg2+ levels along with TRPM6, which is present at the apical level. The CNNM2 gene is crucial for renal magnesium handling, brain development, and neurological functioning. Here, we identified a novel mutation in the CNNM2 gene causing a cognitive delay in a girl with hypomagnesemia. We suggest testing for CNNM2 mutation in patients with neurological impairment and hypomagnesemia.

01 december 2021, Contains fulltext : 244768.pdf (Publisher’s version ) (Open Access), Magnesium is essential for cellular life, but how it is homeostatically controlled still remains poorly understood. Here, we report that members of CNNM family, which have been controversially implicated in both cellular Mg2+ influx and efflux, selectively bind to the TRPM7 channel to stimulate divalent cation entry into cells. Coexpression of CNNMs with the channel markedly increased uptake of divalent cations, which is prevented by an inactivating mutation to the channel's pore. Knockout (KO) of TRPM7 in cells or application of the TRPM7 channel inhibitor NS8593 also interfered with CNNM-stimulated divalent cation uptake. Conversely, KO of CNNM3 and CNNM4 in HEK-293 cells significantly reduced TRPM7-mediated divalent cation entry, without affecting TRPM7 protein expression or its cell surface levels. Furthermore, we found that cellular overexpression of phosphatases of regenerating liver (PRLs), known CNNMs binding partners, stimulated TRPM7-dependent divalent cation entry and that CNNMs were required for this activity. Whole-cell electrophysiological recordings demonstrated that deletion of CNNM3 and CNNM4 from HEK-293 cells interfered with heterologously expressed and native TRPM7 channel function. We conclude that CNNMs employ the TRPM7 channel to mediate divalent cation influx and that CNNMs also possess separate TRPM7-independent Mg2+ efflux activities that contribute to CNNMs' control of cellular Mg2+ homeostasis.

Contains fulltext : 229882.pdf (publisher's version ) (Open Access), Hypomagnesaemia is a common feature of renal Na(+) wasting disorders such as Gitelman and EAST/SeSAME syndrome. These genetic defects specifically affect Na(+) reabsorption in the distal convoluted tubule, where Mg(2+) reabsorption is tightly regulated. Apical uptake via TRPM6 Mg(2+) channels and basolateral Mg(2+) extrusion via a putative Na(+) -Mg(2+) exchanger determines Mg(2+) reabsorption in the distal convoluted tubule. However, the mechanisms that explain the high incidence of hypomagnesaemia in patients with Na(+) wasting disorders of the distal convoluted tubule are largely unknown. In this review, we describe three potential mechanisms by which Mg(2+) reabsorption in the distal convoluted tubule is linked to Na(+) reabsorption. First, decreased activity of the thiazide-sensitive Na(+) /Cl(-) cotransporter (NCC) results in shortening of the segment, reducing the Mg(2+) reabsorption capacity. Second, the activity of TRPM6 and NCC are determined by common regulatory pathways. Secondary effects of NCC dysregulation such as hormonal imbalance, therefore, might disturb TRPM6 expression. Third, the basolateral membrane potential, maintained by the K(+) permeability and Na(+) -K(+) -ATPase activity, provides the driving force for Na(+) and Mg(2+) extrusion. Depolarisation of the basolateral membrane potential in Na(+) wasting disorders of the distal convoluted tubule may therefore lead to reduced activity of the putative Na(+) -Mg(2+) exchanger SLC41A1. Elucidating the interconnections between Mg(2+) and Na(+) transport in the distal convoluted tubule is hampered by the currently available models. Our analysis indicates that the coupling of Na(+) and Mg(2+) reabsorption may be multifactorial and that advanced experimental models are required to study the molecular mechanisms.

01 april 2021, Contains fulltext : 238837.pdf (Publisher’s version ) (Open Access), Hypomagnesemia, seizures, and intellectual disability (HSMR) syndrome is a rare disorder caused by mutations in the cyclin M2 (CNNM2) gene. Due to the limited number of cases, extensive phenotype analyses of these patients have not been performed, hindering early recognition of patients. In this study, we established the largest cohort of HSMR to date, aiming to improve recognition and diagnosis of this complex disorder. Eleven novel variants in CNNM2 were identified in nine single sporadic cases and in two families with suspected HSMR syndrome. (25) Mg(2+) uptake assays demonstrated loss-of-function in seven out of nine variants in CNNM2. Interestingly, the pathogenic mutations resulted in decreased plasma membrane expression. The phenotype of those affected by pathogenic CNNM2 mutations was compared with five previously reported cases of HSMR. All patients suffered from hypomagnesemia (0.44-0.72 mmol/L), which could not be fully corrected by Mg(2+) supplementation. The majority of patients (77%) experienced generalized seizures and exhibited mild to moderate intellectual disability and speech delay. Moreover, severe obesity was present in most patients (89%). Our data establish hypomagnesemia, seizures, intellectual disability, and obesity as hallmarks of HSMR syndrome. The assessment of these major features offers a straightforward tool for the clinical diagnosis of HSMR.