Molecular Pathways and Animal Models of Atrial Septal Defect.

The relative simplicity of the clinical presentation and management of an atrial septal defect belies the complexity of the developmental pathogenesis. Here, we describe the anatomic development of the atrial septum and the venous return to the atrial chambers. Experimental models suggest how mutations and naturally occurring genetic variation could affect developmental steps to cause a defect within the oval fossa, the so-called secundum defect, or other interatrial communications, such as the sinus venosus defect or ostium primum defect.

Mahogunin Ring Finger 1 regulates pigmentation by controlling the pH of melanosomes in melanocytes and melanoma cells.

Mahogunin Ring Finger 1 (MGRN1) is an E3-ubiquitin ligase absent in dark-furred mahoganoid mice. We investigated the mechanisms of hyperpigmentation in Mgrn1-null melan-md1 melanocytes, Mgrn1-KO cells obtained by CRISPR-Cas9-mediated knockdown of Mgrn1 in melan-a6 melanocytes, and melan-a6 cells depleted of MGRN1 by siRNA treatment. Mgrn1-deficient melanocytes showed higher melanin content associated with increased melanosome abundance and higher fraction of melanosomes in highly melanized maturation stages III-IV. Expression, post-translational processing and enzymatic activity of the rate-limiting melanogenic enzyme tyrosinase measured in cell-free extracts were comparable in control and MGRN1-depleted cells. However, tyrosinase activity measured in situ in live cells and expression of genes associated with regulation of pH increased upon MGRN1 repression. Using pH-sensitive fluorescent probes, we found that downregulation of MGRN1 expression in melanocytes and melanoma cells increased the pH of acidic organelles, including melanosomes, strongly suggesting a previously unknown role of MGRN1 in the regulation of melanosomal pH. Among the pH regulatory genes upregulated by Mgrn1 knockdown, we identified those encoding several subunits of the vacuolar adenosine triphosphatase V-ATPase (mostly Atp6v0d2) and a calcium channel of the transient receptor potential channel family, Mucolipin 3 (Mcoln3). Manipulation of expression of the Mcoln3 gene showed that overexpression of Mcoln3 played a significant role in neutralization of the pH of acidic organelles and activation of tyrosinase in MGRN1-depleted cells. Therefore, lack of MGRN1 led to cell-autonomous stimulation of pigment production in melanocytes mostly by increasing tyrosinase specific activity through neutralization of the melanosomal pH in a MCOLN3-dependent manner.

Distribution and Localization of Mahogunin Ring Finger 1 in the Mouse Central Nervous System.

Mahogunin ring finger 1 (MGRN1), an E3 ubiquitin, is involved in several physiological and neuropathological processes. Although mgrn1 mRNA is widely distributed in the central nervous system (CNS), detailed information on its cellular and subcellular localization is lacking and its physiological role remains unclear. In this study, we aimed to determine the distribution of MGRN1 in the mouse CNS using a newly produced antibody against MGRN1. We found that the MGRN1 protein was expressed in most neuronal cell bodies. An intense MGRN1 expression was also observed in the neuropil of the gray matter in different regions of the CNS, including the main olfactory bulb, cerebral cortex, caudate, putamen, thalamic nuclei, hypothalamic nuclei, medial eminence, superior colliculus, hippocampus, dentate gyrus, and spinal cord. Contrastingly, no MGRN1 expression was observed in glial cells. Double fluorescence and immunoelectron microscopic analyses revealed the intracellular distribution of MGRN1 in pre-synapses and near the outer membrane of the mitochondria in neurons. These findings indicate that MGRN1 is more widely expressed throughout the CNS; additionally, the intracellular expression of MGRN1 suggests that it may play an important role in synaptic and mitochondrial functions.

[MGRN1 affects the mitophagy of spermatogonial stem cells in mice].

Objective: To study the effect of mahogunin ring finger-1 (MGRN1) on the mitophagy of the spermatogonial stem cells (SSC) in mice. METHODS: SSCs cultured in vitro were divided into three groups: empty vector control, MGRN1 (MGRN1 in SSCs knocked down by RNAi), and MGRN1 + FCCP (inducing mitophagy with carbonyl cyanide p-trifluoromethoxyphenylhydrazone ï¼»FCCPï¼½ in the SSCs with down-regulated MGRN1). The expressions of mitochondrial function-related proteins (Cytochromo c and COX IV) and mitophagy-related proteins (LC3, P62, FUNDC1 and CK2) and the phosphorylation of FUNDC1 were detected by Western blot. Mitochondria and mitochondrial autophagosomes in the SSCs were observed under the electron microscope. RESULTS: Compared with the empty vector control group, the MGRN1 and MGRN1 + FCCP groups showed significantly down-regulated expressions of Cytochromo c, Cox IV, LC3 and P62, increased phosphorylation level of FUNDC1, and up-regulated expression of CK2 in the SSCs (P < 0.05). No statistically significant differences were found in the expressions of Cytochromo c, Cox IV, LC3, P62 and CK2 or in the phosphorylation level of FUNDC1 between the MGRN1 and MGRN1 + FCCP groups (P > 0.05). Electron microscopy manifested increased mitochondrial damage and reduced mitochondrial autophagosomes in the SSCs in the MGRN1 and MGRN1 + FCCP groups compared with those in the control group. CONCLUSIONS: MGRN1 affects mitophagy in the SSCs of mice, which may be associated with the effect of CK2 on the phosphorylation of FUNDC1, and its molecular mechanism needs to be further studied.

[Influence of MGRN1 on the autophagy of Sertoli cells in mice].

OBJECTIVE: To study the effect of mahogunin ring finger-1 (MGRN1) on the autophagy of Sertoli cells in mice. METHODS: Using RNA interference, we down-regulated the expression of MGRN1 in the mouse TM4 Sertoli cells cultured in vitro, determined the expressions of the autophagy-related proteins LC3-II/I, ATG-5 and ATG-7 by Western blot, and detected the autophagosomes in the TM4 cells by immunofluorescence and electron microscopy. RESULTS: Western blot showed increased expressions of LC3-II/I, ATG-5 and ATG-7 in the mouse TM4 Sertoli cells after knockdown of MGRN1. Fluorescence microscopy revealed significantly more autophagosomes in the TM4 cells than in the control group (P < 0.05). CONCLUSIONS: MGRN1 affects the autophagy of mouse Sertoli cells, and its specific molecular mechanism needs to be further studied.

Human melanocortin 1 receptor-mediated ubiquitination of nonvisual arrestins. Role of Mahogunin Ring Finger 1 E3 ligase.

Signaling from the melanocortin 1 receptor (MC1R), a Gs protein-coupled receptor (GPCR) crucial for melanocyte proliferation and differentiation, is regulated by cytosolic ß-arrestins (ARRBs). MC1R signaling is also negatively modulated by the E3-ubiquitin ligase Mahogunin Ring Finger-1 (MGRN1), whose mutation causes hyperpigmentation, congenital heart defects and neurodegeneration in mice. We showed previously that although MC1R interacts stably with human ARRB1 or ARRB2, only ARRB2 mediates receptor desensitization and internalization. We analyzed MC1R-dependent ARRB ubiquitination, and the possible role of MGRN1. ARRB1 expressed in heterologous cells or human melanoma cells migrated in SDS-PAGE as a 55kDa protein whereas ARRB2 migrated as two major bands of apparent molecular weight near 45 and 55kDa, with an intermediate mobility band occasionally detected. These forms were related by post-translational modification rather than by proteolysis. Presence of MC1R favored expression of the 45kDa protein, the form that interacted preferentially with MC1R. MC1R also mediated poly- or multimonoubiquitination of ARRB2. Ubiquitination was agonist-independent, but required a native MC1R conformation and/or normal receptor trafficking to the plasma membrane, as it was not observed for loss-of-function MC1R variants. In a heterologous expression system, MC1R-dependent ARRB ubiquitination was enhanced by overexpression of MGRN1 and was impaired by siRNA-mediated MGRN1 knockdown thus pointing to MGRN1 as the responsible E3-ligase. Co-immunoprecipitation experiments demonstrated interaction of MGRN1 and ARRBs in the presence of MC1R, suggesting a scaffolding role for the GPCR that may determine the selectivity of E3-ubiquitin ligase engagement and the functional outcome of ARRB ubiquitination.

Ubiquitin-mediated regulation of the E3 ligase GP78 by MGRN1 in trans affects mitochondrial homeostasis.

Cellular quality control provides an efficient surveillance system to regulate mitochondrial turnover. This study elucidates a new interaction between the cytosolic E3 ligase mahogunin RING finger 1 (MGRN1) and the endoplasmic reticulum (ER) ubiquitin E3 ligase GP78 (also known as AMFR). Loss of Mgrn1 function has been implicated in late-onset spongiform neurodegeneration and congenital heart defects, among several developmental defects. Here, we show that MGRN1 ubiquitylates GP78 in trans through non-canonical K11 linkages. This helps maintain constitutively low levels of GP78 in healthy cells, in turn downregulating mitophagy. GP78, however, does not regulate MGRN1. When mitochondria are stressed, cytosolic Ca(2+) increases. This leads to a reduced interaction between MGRN1 and GP78 and its compromised ubiquitylation. Chelating Ca(2+) restores association between the two ligases and the in trans ubiquitylation. Catalytic inactivation of MGRN1 results in elevated levels of GP78 and a consequential increase in the initiation of mitophagy. This is important because functional depletion of MGRN1 by the membrane-associated disease-causing prion protein (Ctm)PrP affects polyubiquitylation and degradation of GP78, also leading to an increase in mitophagy events. This suggests that MGRN1 participates in mitochondrial quality control and could contribute to neurodegeneration in a subset of (Ctm)PrP-mediated prion diseases.

Regulation of Mitofusin1 by Mahogunin Ring Finger-1 and the proteasome modulates mitochondrial fusion.

Health and homoeostasis are maintained by a dynamic balance between mitochondrial fission and fusion. Mitochondrial fusion machinery is largely unknown in mammals. Only a few reports have illustrated the role of Fzo1 in mitochondrial fusion known in Saccharomyces cerevisiae. We demonstrate that the ubiquitin ligase Mahogunin Ring Finger-1 (MGRN1) interacts with and constitutively ubiquitinates the mammalian homolog, Mitofusin1 (Mfn1) via K63 linkages. In mice models, loss of Mgrn1 function leads to severe developmental defects and adult-onset spongiform neurodegeneration, similar to prion diseases. The tethering of mitochondria to form the ~180kDa Mfn1 complex is independent of MGRN1-mediated ubiquitination. However, successful mitochondrial fusion requires formation of higher oligomers of Mfn1 which in turn needs GTPase activity, intact heptad repeats of Mfn1 and ubiquitination by MGRN1. Following ubiquitination, proteasomal processing of Mfn1 completes the mitochondrial fusion process. This step requires functional p97 activity. These findings suggest a sequence of events where GTPase activity of Mfn1 and tethering of adjacent mitochondria precedes its MGRN1-mediated ubiquitination and proteasomal degradation culminating in mitochondrial fusion.

Mahogunin ring finger 1 confers cytoprotection against mutant SOD1 aggresomes and is defective in an ALS mouse model.

Proteotoxicity of misfolded, disease-causing proteins is deeply implicated in the pathomechanisms for neurodegenerative diseases including copper-zinc superoxide dismutase (SOD1)-linked amyotrophic lateral sclerosis (ALS). However, the precise cellular quality control (QC) mechanisms against aggregation of misfolded mutant SOD1 proteins remain elusive. Here, we found that the Mahogunin ring finger-1 (MGRN1) E3 ubiquitin ligase, which catalyzes mono-ubiquitination to the substrate, was dysregulated in the cellular and mouse models of ALS and that it preferentially interacted with various mutant forms of SOD1. Intriguingly, the motor neurons of presymptomatic ALS mice have diminished MGRN1 cytoplasmic distribution. MGRN1 was partially recruited to mutant SOD1 inclusions where they were positive for p62 and Lamp2. Moreover, overexpression of MGRN1 reduced mutant SOD1 aggregation and alleviated its proteotoxic effects on cells. Taken together, our findings suggest that MGRN1 contributes to the clearance of toxic mutant SOD1 inclusions likely through autophagic pathway, and, most likely, the sequestration of MGRN1 sensitizes motor neurons to degeneration in the ALS mouse model. Furthermore, the present study identifies the MGRN1-mediated protein QC mechanism as a novel therapeutic target in neurodegenerative diseases.

Mahogunin-mediated regulation of Gαi localisation during mitosis and its effect on spindle positioning.

Mahogunin RING Finger 1 (MGRN1) is a ubiquitin E3 ligase known to affect spindle tilt in mitotic cells by regulating α-tubulin ubiquitination and polymerization. In cell culture systems we have found that expressing truncated mutants of MGRN1 leads to various other mitotic anomalies, such as lateral and angular spindle displacements. This seems to be independent of the MGRN1 ligase activity. Our experiments suggest that MGRN1 regulates the balance between the lower molecular weight monomeric Gαi and larger trimeric G-protein complex, along with its abundance in the ternary complex that regulates spindle positioning. The cytosolic isoforms of MGRN1 lead to the enrichment of monomeric Gαi in the cytosol and its subsequent recruitment at the plasma membrane. Excess Gαi at the cell cortex results in an imbalance in the assembly of the ternary complex regulating spindle positioning during mitosis. These observations seem independent of the ligase activity of MGRN1, although we cannot exclude the involvement of an intermediate player that acts as a substrate for MGRN1, and in turn, regulates Gαi.

Pleiotropic effects of coat colour-associated mutations in humans, mice and other mammals.

The characterisation of the pleiotropic effects of coat colour-associated mutations in mammals illustrates that sensory organs and nerves are particularly affected by disorders because of the shared origin of melanocytes and neurocytes in the neural crest; e.g. the eye-colour is a valuable indicator of disorders in pigment production and eye dysfunctions. Disorders related to coat colour-associated alleles also occur in the skin (melanoma), reproductive tract and immune system. Additionally, the coat colour phenotype of an individual influences its general behaviour and fitness. Mutations in the same genes often produce similar coat colours and pleiotropic effects in different species (e.g., KIT [reproductive disorders, lethality], EDNRB [megacolon] and LYST [CHS]). Whereas similar disorders and similar-looking coat colour phenotypes sometimes have a different genetic background (e.g., deafness [EDN3/EDNRB, MITF, PAX and SNAI2] and visual diseases [OCA2, RAB38, SLC24A5, SLC45A2, TRPM1 and TYR]). The human predilection for fancy phenotypes that ignore disorders and genetic defects is a major driving force for the increase of pleiotropic effects in domestic species and laboratory subjects since domestication has commenced approximately 18,000 years ago.

Mahogunin ring finger 1 suppresses misfolded polyglutamine aggregation and cytotoxicity.

Polyglutamine diseases are a family of inherited neurodegenerative diseases caused by the expansion of CAG repeats within the coding region of target genes. Still the mechanism(s) by which polyglutamine proteins are ubiquitinated and degraded remains obscure. Here, for the first time, we demonstrate that Mahogunin 21 ring finger 1 E3 ubiquitin protein ligase is depleted in cells that express expanded-polyglutamine proteins. MGRN1 co-immunoprecipitates with expanded-polyglutamine huntingtin and ataxin-3 proteins. Furthermore, we show that MGRN1 is predominantly colocalized and recruits with polyglutamine aggregates in both cellular and transgenic mouse models. Finally, we demonstrate that the partial depletion of MGRN1 increases the rate of aggregate formation and cell death, whereas the overexpression of MGRN1 reduces the frequency of aggregate formation and provides cytoprotection against polyglutamine-induced proteotoxicity. These observations suggest that stimulating the activity of MGRN1 ubiquitin ligase might be a potential therapeutic target to eliminate the cytotoxic threat in polyglutamine diseases.

MGRN1 depletion promotes intercellular adhesion in melanoma by upregulation of E-cadherin and inhibition of CDC42.

Mahogunin Ring Finger 1 is an E3-ubiquitin ligase encoded by the color gene MGRN1. Our previous in vitro and in vivo studies demonstrated that Mgrn1 deletion in mouse melanoma cells induced cell differentiation and adhesion, and decreased cell motility and invasion on collagen I, and lung colonization in an in vivo model. Here, we investigated the role of MGRN1 on human melanoma cell morphology, adhesion and expression of genes/proteins involved in an EMT-like transition. We demonstrated that wild-type BRAF human melanoma cells adopted a clustering-like morphology on collagen I, with permanent MGRN1 abrogation resulting in bigger cell clusters. Enhanced intercellular adhesion was mostly mediated by induction of E-cadherin and higher co-localization with ß-catenin. Transcriptional upregulation of E-cadherin likely occurred through downregulation of the ZEB1 repressor. Finally, pulldown assays showed reduced activation of CDC42 in the absence of MGRN1, which was reverted after E-cadherin silencing. Overall, these findings highlight a new MGRN1-dependent pathway regulating melanoma cell shape, motility, and invasion potential.

MGRN1 as a Phenotypic Determinant of Human Melanoma Cells and a Potential Biomarker.

Mahogunin Ring Finger 1 (MGRN1), a ubiquitin ligase expressed in melanocytes, interacts with the α melanocyte-stimulating hormone receptor, a well-known melanoma susceptibility gene. Previous studies showed that MGRN1 modulates the phenotype of mouse melanocytes and melanoma cells, with effects on pigmentation, shape, and motility. Moreover, MGRN1 knockdown augmented the burden of DNA breaks in mouse cells, indicating that loss of MGRN1 promoted genomic instability. However, data concerning the roles of MGRN1 in human melanoma cells remain scarce. We analyzed MGRN1 knockdown in human melanoma cells. Transient MGRN1 depletion with siRNA or permanent knockdown in human melanoma cells by CRISPR/Cas9 caused an apparently MITF-independent switch to a more dendritic phenotype. Lack of MGRN1 also increased the fraction of human cells in the S phase of the cell cycle and the burden of DNA breaks but did not significantly impair proliferation. Moreover, in silico analysis of publicly available melanoma datasets and estimation of MGRN1 in a cohort of clinical specimens provided preliminary evidence that MGRN1 expression is higher in human melanomas than in normal skin or nevi and pointed to an inverse correlation of MGRN1 expression in human melanoma with patient survival, thus suggesting potential use of MGRN1 as a melanoma biomarker.

Receptor control by membrane-tethered ubiquitin ligases in development and tissue homeostasis.

Paracrine cell-cell communication is central to all developmental processes, ranging from cell diversification to patterning and morphogenesis. Precise calibration of signaling strength is essential for the fidelity of tissue formation during embryogenesis and tissue maintenance in adults. Membrane-tethered ubiquitin ligases can control the sensitivity of target cells to secreted ligands by regulating the abundance of signaling receptors at the cell surface. We discuss two examples of this emerging concept in signaling: (1) the transmembrane ubiquitin ligases ZNRF3 and RNF43 that regulate WNT and bone morphogenetic protein receptor abundance in response to R-spondin ligands and (2) the membrane-recruited ubiquitin ligase MGRN1 that controls Hedgehog and melanocortin receptor abundance. We focus on the mechanistic logic of these systems, illustrated by structural and protein interaction models enabled by AlphaFold. We suggest that membrane-tethered ubiquitin ligases play a widespread role in remodeling the cell surface proteome to control responses to extracellular ligands in diverse biological processes.

Promoter Methylation of the MGRN1 Gene Predicts Prognosis and Response to Chemotherapy of High-Grade Serous Ovarian Cancer Patients.

Aberrant DNA methylation is considered to play a critical role in the chemoresistance of epithelial ovarian cancer (EOC). In this study, we explored the relationship between hypermethylation of the Mahogunin Ring Finger 1 (MGRN1) gene promoter and primary chemoresistance and clinical outcomes in high-grade serous ovarian cancer (HGSOC) patients. The MALDI-TOF mass spectrometry assays revealed a strong association between hypermethylation of the MGRN1 upstream region and platinum resistance in HGSOC patients. Spearman's correlation analysis revealed a significantly negative connection between the methylation level of MGRN1 and its expression in HGSOC. In vitro analysis demonstrated that knockdown of MGRN1 reduced the sensitivity of cells to cisplatin and that expression of EGR1 was significantly decreased in SKOV3 cells with low levels of MGRN1 expression. Similarly, EGR1 mRNA expression was lower in platinum-resistant HGSOC patients and was positively correlated with MGRN1 mRNA expression. Kaplan-Meier analyses showed that high methylation of the MGRN1 promoter region and low expression of MGRN1 were associated with worse survival of HGSOC patients. In multivariable models, low MGRN1 expression was an independent factor predicting poor outcome. Furthermore, low expression of EGR1 was also been confirmed to be significantly related to the poor prognosis of HGSOC patients by Kaplan-Meier. The hypermethylation of the MGRN1 promoter region and low expression of MGRN1 were associated with platinum resistance and poor outcomes in HGSOC patients, probably by altering EGR1 expression.

DNA methylation array analysis identifies breast cancer associated RPTOR, MGRN1 and RAPSN hypomethylation in peripheral blood DNA.

DNA methylation changes in peripheral blood DNA have been shown to be associated with solid tumors. We sought to identify methylation alterations in whole blood DNA that are associated with breast cancer (BC). Epigenome-wide DNA methylation profiling on blood DNA from BC cases and healthy controls was performed by applying Infinium HumanMethylation450K BeadChips. Promising CpG sites were selected and validated in three independent larger sample cohorts via MassARRAY EpiTyper assays. CpG sites located in three genes (cg06418238 in RPTOR, cg00736299 in MGRN1 and cg27466532 in RAPSN), which showed significant hypomethylation in BC patients compared to healthy controls in the discovery cohort (p < 1.00 x 10-6) were selected and successfully validated in three independent cohorts (validation I, n =211; validation II, n=378; validation III, n=520). The observed methylation differences are likely not cell-type specific, as the differences were only seen in whole blood, but not in specific sub cell-types of leucocytes. Moreover, we observed in quartile analysis that women in the lower methylation quartiles of these three loci had higher ORs than women in the higher quartiles. The combined AUC of three loci was 0.79 (95%CI 0.73-0.85) in validation cohort I, and was 0.60 (95%CI 0.54-0.66) and 0.62 (95%CI 0.57-0.67) in validation cohort II and III, respectively. Our study suggests that hypomethylation of CpG sites in RPTOR, MGRN1 and RAPSN in blood is associated with BC and might serve as blood-based marker supplements for BC if these could be verified in prospective studies.

Mahogunin Ring Finger-1 (MGRN1), a Multifaceted Ubiquitin Ligase: Recent Unraveling of Neurobiological Mechanisms.

In healthy cell, inappropriate accumulation of poor or damaged proteins is prevented by cellular quality control system. Autophagy and ubiquitin proteasome system (UPS) provides regular cytoprotection against proteotoxicity induced by abnormal or disruptive proteins. E3 ubiquitin ligases are crucial components in this defense mechanism. Mahogunin Ring Finger-1 (MGRN1), an E3 ubiquitin ligase of the Really Interesting New Gene (RING) finger family, plays a pivotal role in many biological and cellular mechanisms. Previous findings indicate that lack of functions of MGRN1 can cause spongiform neurodegeneration, congenital heart defects, abnormal left-right patterning, and mitochondrial dysfunctions in mice brains. However, the detailed molecular pathomechanism of MGRN1 in cellular functions and diseases is not well known. This article comprehensively represents the molecular nature, characterization, and functions of MGRN1; we also summarize possible beneficiary aspects of this novel E3 ubiquitin ligase. Here, we review recent literature on the role of MGRN1 in the neuro-pathobiological mechanisms, with precise focus on the processes of neurodegeneration, and thereby propose new lines of potential targets for therapeutic intervention.

RML prions act through Mahogunin and Attractin-independent pathways.

While the conversion of the normal form of prion protein to a conformationally distinct pathogenic form is recognized to be the primary cause of prion disease, it is not clear how this leads to spongiform change, neuronal dysfunction and death. Mahogunin ring finger-1 (Mgrn1) and Attractin (Atrn) null mutant mice accumulate vacuoles throughout the brain that appear very similar to those associated with prion disease, but they do not accumulate the protease-resistant scrapie form of the prion protein or become sick. A study demonstrating an interaction between cytosolically-exposed prion protein and MGRN1 suggested that disruption of MGRN1 function may contribute to prion disease pathogenesis, but we recently showed that neither loss of MGRN1 nor MGRN1 overexpression influences the onset or progression of prion disease following intracerebral inoculation with Rocky Mountain Laboratory prions. Here, we show that loss of ATRN also has no effect on prion disease onset or progression and discuss possible mechanisms that could cause vacuolation of the central nervous system in Mgrn1 and Atrn null mutant mice and whether the same pathways might contribute to this intriguing phenotype in prion disease.

Functional conservation between mammalian MGRN1 and plant LOG2 ubiquitin ligases.

Plant LOSS OF GDU 2 (LOG2) and Mammalian Mahogunin Ring Finger 1 (MGRN1) proteins are RING-type E3 ligases sharing similarity N-terminal to the RING domain. Deletion of this region disrupts the interaction of LOG2 with the plant membrane protein GLUTAMINE DUMPER1 (GDU1). Phylogenetic analysis identified two clades of LOG2/MGRN1-like proteins in vertebrates and plants. The ability of MGRN1 to functionally replace LOG2 was tested. MGRN1 ubiquitylates GDU1 in vitro and can partially substitute for LOG2 in the plant, partially restoring amino acid resistance to a GDU1-myc over-expression, log2-2 background. Altogether, these results suggest a conserved function for the N-terminal domain in evolution.