Distinct gut microbiota signatures associated with progression of atherosclerosis in people living with HIV.

BACKGROUND: The relationship of microbiota composition dynamics and the progression of subclinical atherosclerosis in people with HIV (PWH) remains unknown. METHODS: 96-week, prospective, longitudinal study in virologically-suppressed PWH. Carotid intima-media thickness (cIMT) measurements and stool samples were obtained at baseline, 48-week and 96-week visits. cIMT progression was defined as an increase >10% and/or detection of new carotid plaque. To profile the gut microbiome, amplification and sequencing of 16S ribosomal-RNA (V3-V4 variable regions) were carried out following the Illumina protocol. Sequencing was performed with MiSeq platform. RESULTS: 191, 190 and 167 patients had available fecal samples for microbiome analysis at the baseline, 48- and 96-week visits, respectively. 87 (43%) participants showed atherosclerosis progression, and 54 (26.7%) presented new carotid plaque. No significant differences were observed in adjusted α-diversity indices between groups defined by cIMT progression. Beta-diversity determined through principal coordinate analysis distances showed that the groups exhibited distinct microbial profiles (PERMANOVA p-value = 0.03). Longitudinal analysis with ANCOM-BC2 adjusted for traditional cardiovascular risk factors, MSM and nadir CD4 count revealed that cIMT progression was consistently associated with Agathobacter and Ruminococcus_2, while non-progression was consistently associated with Prevotella_7. CONCLUSION: Progression of atherosclerosis in PWH might be associated with distinctive signatures in the gut microbiota.

Integrating SARS-CoV-2-specific interferon-γ release assay testing in the evaluation of patients hospitalized with COVID-19.

IMPORTANCE: The cellular immune response is essential in the protection against severe disease in patients with established SARS-CoV-2 infection. The novelty of this study lies in the evaluation of the overall performance of a standardized assay to measure cellular immune response, the SARS-CoV-2-specific interferon-γ release assay (IGRA), in hospitalized patients with severe COVID-19. The SARS-CoV-2 IGRA was shown to accurately classify patients based on disease severity and prognosis, and the study revealed that test performance was not affected by the SARS-CoV-2 variant or control tube results. We identified an assay cut-off point with a high negative predictive value against mortality. The SARS-CoV-2 IGRA in patients hospitalized for COVID-19 may be a useful tool to assess cellular immunity and adopt targeted therapeutic and preventive measures.

T-Cell Immunity Against Severe Acute Respiratory Syndrome Coronavirus 2 Measured by an Interferon-γ Release Assay Is Strongly Associated With Patient Outcomes in Vaccinated Persons Hospitalized With Delta or Omicron Variants.

BACKGROUND: We measured T-cell and antibody responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in vaccinated patients hospitalized for coronavirus disease 2019 (COVID-19) and explored their potential value to predict outcomes. METHODS: This was a prospective, longitudinal study including vaccinated patients hospitalized with Delta and Omicron SARS-CoV-2 variants. TrimericS-IgG antibodies and SARS-CoV-2 T-cell response were measured using a specific quantitative interferon-γ release assay (IGRA). Primary outcome was all-cause 28-day mortality or need for intensive care unit (ICU) admission. Cox models were used to assess associations with outcomes. RESULTS: Of 181 individuals, 158 (87.3%) had detectable SARS-CoV-2 antibodies, 92 (50.8%) showed SARS-CoV-2-specific T-cell responses, and 87 (48.1%) had both responses. Patients who died within 28 days or were admitted to ICU were less likely to have both unspecific and specific T-cell responses in IGRA. In adjusted analyses (adjusted hazard ratio [95% confidence interval]), for the entire cohort, having both T-cell and antibody responses at admission (0.16 [.05-.58]) and Omicron variant (0.38 [.17-.87]) reduced the hazard of 28-day mortality or ICU admission, whereas higher Charlson comorbidity index score (1.27 [1.07-1.51]) and lower oxygen saturation to fraction of inspired oxygen ratio (2.36 [1.51-3.67]) increased the risk. CONCLUSIONS: Preexisting immunity against SARS-CoV-2 is strongly associated with patient outcomes in vaccinated individuals requiring hospital admission for COVID-19. Persons showing both T-cell and antibody responses have the lowest risk of severe outcomes.

Human Immunodeficiency Virus Type 1 RNA Levels in Rectal and Seminal Compartments After Switching to Long-Acting Cabotegravir Plus Rilpivirine: A Longitudinal Study.

Human immunodeficiency virus type 1 RNA levels were longitudinally evaluated in 211 rectal and 152 seminal samples from 12 virologically suppressed participants switching to monthly long-acting cabotegravir plus rilpivirine or continuing with daily dolutegravir-abacavir-lamivudine. Maintenance of viral suppression in rectal and seminal compartments was comparable, and blips occurred with similar frequency with both treatment regimens. CLINICAL TRIALS REGISTRATION: NCT02938520.

Robust long-term immunity to SARS-CoV-2 in patients recovered from severe COVID-19 after interleukin-6 blockade.

BACKGROUND: Whether interleukin-6 (IL-6) blockade in patients with COVID-19 will affect the protective immunity against SARS-CoV-2 has become an important concern for anti-IL-6 therapy. We aimed to investigate the effects of IL-6 blockade on long-term immunity to SARS-CoV-2. METHODS: Prospective, longitudinal cohort study conducted in patients hospitalized for severe or critical COVID-19 with laboratory confirmed SARS-CoV-2 infection. We assessed humoral (anti-S1 domain of the spike [S], anti-nucleocapsid [N], anti-trimeric spike [TrimericS] IgG, and neutralizing antibodies [Nab]) and T-cell (interferon-γ release assay [IGRA]) responses and evaluated the incidence of reinfections over one year after infection in patients undergoing IL-6 blockade with tocilizumab and compared them with untreated subjects. FINDINGS: From 150 adults admitted with confirmed SARS-CoV-2 infection, 78 were 1:1 propensity score-matched. Patients receiving anti-IL6 therapy showed a shorter time to S-IgG seropositivity and stronger S-IgG and N-IgG antibody responses. Among unvaccinated subjects one year after infection, median (Q1-Q3) levels of TrimericS-IgG (295 vs 121 BAU/mL; p = 0.011) and Nab (74.7 vs 41.0 %IH; p = 0.012) were higher in those undergoing anti-IL6 therapy, and a greater proportion of them had Nab (80.6% vs 57.7%; p = 0.028). T-cell immunity was also better in those treated with anti-IL6, with higher median (Q1-Q3) interferon-γ responses (1760 [702-3992] vs 542 [35-1716] mIU/mL; p = 0.013) and more patients showing positive T-cell responses in the IGRA one year after infection. Patients treated with anti-IL6 had fewer reinfections during follow-up and responded to vaccination with robust increase in both antibody and T-cell immunity. INTERPRETATION: IL-6 blockade in patients with severe COVID-19 does not have deleterious effects on long-term immunity to SARS-CoV-2. The magnitude of both antibody and T-cell responses was stronger than the observed in non-anti-cytokine-treated patients with no increase in the risk of reinfections. FUNDING: Instituto de Salud Carlos-III (Spain).

Pericarditis caused by Mycobacterium africanum: case report.

BACKGROUND: Mycobacterium africanum is a member of the Mycobacterium tuberculosis complex (MTBC) and is endemic in West Africa, where it causes up to half of all cases of pulmonary tuberculosis. Here, we report the first isolation of Mycobacterium africanum from the pericardial effusion culture of a patient with tuberculous pericarditis. CASE PRESENTATION: A 31-year-old man, native from Senegal, came to the emergency room with massive pericardial effusion and cardiac tamponade requiring pericardiocentesis. M. africanum subtype II was identified in the pericardial fluid. The patient completed 10 months of standard treatment, with a favorable outcome. CONCLUSIONS: We report the first case of tuberculous pericarditis caused by Mycobacterium africanum, which provide evidence that this microorganism can cause pericardial disease and must be considered in patients from endemic areas presenting with pericardial effusion.

Survival benefit of remdesivir in hospitalized COVID-19 patients with high SARS-CoV-2 viral loads and low-grade systemic inflammation.

OBJECTIVES: To assess the benefits of remdesivir in hospitalized COVID-19 patients receiving combined immunomodulatory therapy (CIT) with dexamethasone and tocilizumab. METHODS: This was a cohort study of microbiologically confirmed COVID-19 hospitalized patients. The primary outcome was all-cause 28 day mortality. Secondary outcomes were need for invasive mechanical ventilation (IMV) and IMV/death. Subgroup analyses according to SARS-CoV-2 cycle threshold (Ct) values and inflammation biomarkers were performed. Multivariable marginal structural Cox proportional hazards regression models were used to analyse the association between remdesivir therapy and the risk of outcomes of interest. RESULTS: Of 1368 hospitalized patients treated with corticosteroids, 1014 (74%) also received tocilizumab, 866 (63%) remdesivir and 767 (56%) tocilizumab + remdesivir. The 28 day mortality was 9% in the overall cohort, with an adjusted HR (aHR) of 0.32 (95% CI = 0.17-0.59) for patients receiving CIT. In the latter group, the 28 day mortality was 6.5%, with an aHR of 1.11 (95% CI = 0.57-2.16) for remdesivir use and there were no differences in secondary outcomes. The risk of primary and secondary outcomes with remdesivir differed by Ct and C-reactive protein (CRP) levels in patients receiving CIT: for 28 day mortality, the aHR was 0.48 (95% CI = 0.21-1.11) for Ct <25, 0.12 (95% CI = 0.02-0.66) for Ct <25 and <5 day symptom duration and 0.13 (95% CI = 0.03-0.50) for CRP <38 mg/L; for IMV and IMV/death, the aHR was 0.32 (95% CI = 0.13-0.77) and 0.33 (95% CI = 0.17-0.63), respectively, in patients with Ct <25. CONCLUSIONS: The benefits of remdesivir administered with dexamethasone and tocilizumab in hospitalized COVID-19 patients differ depending on Ct and CRP. Remdesivir decreases the risk of mortality and need for IMV in patients with high viral loads and low-grade systemic inflammation.

Clinical Performance of a Standardized Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Interferon-γ Release Assay for Simple Detection of T-Cell Responses After Infection or Vaccination.

BACKGROUND: We evaluated a standardized interferon-γ (IFN-γ) release assay (IGRA) for detection of T-cell immune response after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or vaccination. METHODS: This prospective study included patients with coronavirus disease 2019 (COVID-19) with different severity of illness and follow-up (FU), vaccinated subjects, and healthy unvaccinated persons. SARS-CoV-2 T-cell response was measured using a specific quantitative IGRA in whole blood (Euroimmun, Germany) and TrimericS-IgG and neutralizing antibodies with validated serological platforms. Positivity of reverse transcription-polymerase chain reaction or vaccination was considered as the reference standard. RESULTS: A total of 239 individuals were included (152 convalescent, 54 vaccinated, and 33 uninfected unvaccinated). Overall sensitivity, specificity, and positive- and negative-predictive values (95% confidence interval) of the IGRA were 81.1% (74.9-86%), 90.9% (74.5-97.6%), 98.2% (94.5-99.5%), and 43.5% (31.8-55.9%), respectively. All vaccinated SARS-CoV-2-naive subjects had positive IGRA at 3 months. In convalescent subjects the magnitude of IFN-γ responses and IGRA accuracy varied according to disease severity and duration of FU, with the best performance in patients with severe COVID-19 at 3 months and the worst in those with mild disease at 12 months. The greatest contribution of IGRA to serological tests was observed in patients with mild disease and long-term FU (incremental difference, 30.4%). CONCLUSIONS: The IGRA was a reliable method of quantifying T-cell response after SARS-COV-2 infection or vaccination. In convalescent patients, the sensitivity is largely dependent on disease severity and time since primary infection. The assay is more likely to add clinical value to serology in patients with mild infections.

Impact of the Addition of Baricitinib to Standard of Care Including Tocilizumab and Corticosteroids on Mortality and Safety in Severe COVID-19.

Background: Baricitinib is a Janus kinase (JAK) inhibitor with a broader anti-inflammatory activity than tocilizumab and an antiviral potential although no head-to-head trials are available. The benefits of adding baricitinib to patients with COVID-19 experiencing clinical progression despite the standard of care (SOC), including corticosteroids and tocilizumab, are also unknown. Methods: A cohort study included microbiologically confirmed COVID-19 hospitalizations. The primary outcome was 28-day mortality. Secondary outcomes were 60- and 90-day mortality, the composite outcome "28-day invasive mechanical ventilation (IMV) or death" and the safety of the combination. Propensity score (PS) matching was used to identify the association between baricitinib use and the outcomes of interest. Results: Of 1,709 admissions, 994 patients received corticosteroids and tocilizumab and 110 of them received baricitinib after tocilizumab. PS matched 190 (95:95) patients with baricitinib + SOC vs. SOC, of whom 69.5% received remdesivir. No significant effect of baricitinib was observed on 28-day [39 events; adjusted hazard ratio (aHR), 0.76; 95% CI, 0.31-1.86], 60-day (49 events, aHR, 1.17; 95% CI, 0.55-2.52), or 90-day mortality (49 events; aHR, 1.14; 95% CI, 0.53-2.47), or on the composite outcome 28-day IMV/death (aHR, 0.88; 95% CI, 0.45-1.72). Secondary infections during hospitalization were not different between groups (17.9 vs. 10.5%, respectively; p = 0.212) and thromboembolic events were higher with baricitinib (11.6% vs. 3.2%; p = 0.048), but differences vanished after the adjustment [aHR 1.89 (0.31-11.57), p = 0.490]. Conclusion: The addition of baricitinib did not substantially reduce mortality in hospitalized patients with COVID-19 having clinical progression despite the therapy with tocilizumab and corticosteroids. The combination of baricitinib and tocilizumab was not associated with an increased risk of secondary infections or thromboembolic events.

Late reinfection with a different severe acute respiratory syndrome coronavirus-2 clade in a patient with refractory arterial hypertension: a case report.

BACKGROUND: Differentiating between persistent infection with intermittent viral shedding and reinfection with severe acute respiratory syndrome coronavirus 2 remains challenging. Although a small number of cases with genomic evidence of second infection have been reported, limited information exists on frequency and determinants of reinfection, time between infections, and duration of immunity after the primary infection. CASE PRESENTATION: We report a reinfection with severe acute respiratory syndrome coronavirus 2 in a 52-year-old caucasian male whose primary infection was diagnosed in May 2020, during the first wave of the pandemic in Spain, and the second occurred 8 months later, in January 2021. We present a complete dataset including results from real-time polymerase chain reaction, serology, and genome sequencing confirming reinfection with a different clade. Noteworthy was that the patient was immunocompetent but had multiple cardiometabolic comorbidities, including refractory arterial hypertension, that might increase the individual risk in coronavirus disease 2019. CONCLUSIONS: This case of reinfection with severe acute respiratory syndrome coronavirus 2 occurring several months after the primary infection reports the longest time interval between reinfection and initial infection described to date. It raises concerns on the duration of protective immunity, suggesting that it may begin to wane in patients who acquired the initial infection during the first wave of the pandemic. The potential contributing role of arterial hypertension and cardiometabolic comorbidities as risk factors for reinfection deserves investigation.

SARS-CoV-2 Seroconversion and Viral Clearance in Patients Hospitalized With COVID-19: Viral Load Predicts Antibody Response.

BACKGROUND: The interdependencies of viral replication and the host immune response in patients with coronavirus disease 2019 (COVID-19) remain to be defined. We investigated the viral determinants of antibody response, the predictors of nonseroconversion, and the role of antibodies on viral dynamics. METHODS: This was a prospective study in patients hospitalized with COVID-19 that was microbiologically confirmed by real-time polymerase chain reaction (RT-PCR). Serial nasopharyngeal and oropharyngeal swabs and plasma samples were obtained for measuring severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA and antibodies (total and S-IgG/N-IgG), respectively. RESULTS: Of 132 patients included, 99 (75%) showed positive antibody titers after a median (Q1-Q3) of 11 (8-14) days. The median (Q1-Q3) follow-up was 74.5 (63.0-87.0) days. In an adjusted linear regression model, time to seropositivity was inversely associated with peak log SARS-CoV-2 viral load (P = .009) and positively with time to viral clearance (P = .004). Adjusted predictors of S-IgG levels were time to viral clearance (P < .001), bilateral lung infiltrates on admission (P = .011), and the time-dependent SARS-CoV-2 RNA (P < .001) and SARS-CoV-2 RNA area under the curve (P = .001). Thirty-three (25%) patients showed undetectable antibody titers. Patients who did not seroconvert had higher cycle threshold values of RT-PCR (38.0 vs 28.0; P < .001), had shorter time to viral clearance (3.0 vs 41.0; P < .001), and were more likely to have SARS-CoV-2 only detected on fecal samples (P < .001). Nonseroconvertors had also lower levels of blood inflammatory biomarkers on admission and lower disease severity. CONCLUSIONS: Viral replication determines the magnitude of antibody response to SARS-CoV-2, which, in turn, contributes to viral clearance. COVID-19 patients who do not seroconvert exhibit a differential virological and clinical profile.

Magnesium accumulation upon cyclin M4 silencing activates microsomal triglyceride transfer protein improving NASH.

BACKGROUND & AIMS: Perturbations of intracellular magnesium (Mg2+) homeostasis have implications for cell physiology. The cyclin M family, CNNM, perform key functions in the transport of Mg2+ across cell membranes. Herein, we aimed to elucidate the role of CNNM4 in the development of non-alcoholic steatohepatitis (NASH). METHODS: Serum Mg2+ levels and hepatic CNNM4 expression were characterised in clinical samples. Primary hepatocytes were cultured under methionine and choline deprivation. A 0.1% methionine and choline-deficient diet, or a choline-deficient high-fat diet were used to induce NASH in our in vivo rodent models. Cnnm4 was silenced using siRNA, in vitro with DharmaFECT and in vivo with Invivofectamine® or conjugated to N-acetylgalactosamine. RESULTS: Patients with NASH showed hepatic CNNM4 overexpression and dysregulated Mg2+ levels in the serum. Cnnm4 silencing ameliorated hepatic lipid accumulation, inflammation and fibrosis in the rodent NASH models. Mechanistically, CNNM4 knockdown in hepatocytes induced cellular Mg2+ accumulation, reduced endoplasmic reticulum stress, and increased microsomal triglyceride transfer activity, which promoted hepatic lipid clearance by increasing the secretion of VLDLs. CONCLUSIONS: CNNM4 is overexpressed in patients with NASH and is responsible for dysregulated Mg2+ transport. Hepatic CNNM4 is a promising therapeutic target for the treatment of NASH. LAY SUMMARY: Cyclin M4 (CNNM4) is overexpressed in non-alcoholic steatohepatitis (NASH) and promotes the export of magnesium from the liver. The liver-specific silencing of Cnnm4 ameliorates NASH by reducing endoplasmic reticulum stress and promoting the activity of microsomal triglyceride transfer protein.

Structural Insights into the Intracellular Region of the Human Magnesium Transport Mediator CNNM4.

The four member family of "Cyclin and Cystathionine ß-synthase (CBS) domain divalent metal cation transport mediators", CNNMs, are the least-studied mammalian magnesium transport mediators. CNNM4 is abundant in the brain and the intestinal tract, and its abnormal activity causes Jalili Syndrome. Recent findings show that suppression of CNNM4 in mice promotes malignant progression of intestinal polyps and is linked to infertility. The association of CNNM4 with phosphatases of the regenerating liver, PRLs, abrogates its Mg2+-efflux capacity, thus resulting in an increased intracellular Mg2+ concentration that favors tumor growth. Here we present the crystal structures of the two independent intracellular domains of human CNNM4, i.e., the Bateman module and the cyclic nucleotide binding-like domain (cNMP). We also derive a model structure for the full intracellular region in the absence and presence of MgATP and the oncogenic interacting partner, PRL-1. We find that only the Bateman module interacts with ATP and Mg2+, at non-overlapping sites facilitating their positive cooperativity. Furthermore, both domains dimerize autonomously, where the cNMP domain dimer forms a rigid cleft to restrict the Mg2+ induced sliding of the inserting CBS1 motives of the Bateman module, from a twisted to a flat disk shaped dimer.

Current Structural Knowledge on the CNNM Family of Magnesium Transport Mediators.

The cyclin and cystathionine ß-synthase (CBS) domain magnesium transport mediators, CNNMs, are key players in maintaining the homeostasis of magnesium in different organs. The human family includes four members, whose impaired activity causes diseases such as Jalili Syndrome or Familial Hypomagnesemia, but is also linked to neuropathologic disorders, altered blood pressure, and infertility. Recent findings demonstrated that CNNMs are associated with the highly oncogenic phosphatases of the regenerating liver to promote tumor growth and metastasis, which has attracted renewed focus on their potential exploitation as targets for cancer treatment. However, the exact function of CNNMs remains unclear and is subject to debate, proposed as either direct transporters, sensors, or homeostatic factors. This review gathers the current structural knowledge on the CNNM family, highlighting similarities and differences with the closely related structural partners such as the bacterial Mg2+/Co2+ efflux protein CorC and the Mg2+ channel MgtE.

Novel Aspects of Renal Magnesium Homeostasis.

Magnesium (Mg2+) is indispensable for several vital functions, such as neurotransmission, cardiac conductance, blood glucose, blood pressure regulation, and proper function of more than 300 enzymes. Thus, Mg2+ homeostasis is subject to tight regulation. Besides the fast and immediate regulation of plasma Mg2+, a major part of Mg2+ homeostasis is realized by a concerted action of epithelial molecular structures that tightly control intestinal uptake and renal absorption. This mechanism is provided by a combination of para- and transcellular pathways. Whereas the first pathway provides the organism with a maximal amount of vital substances by a minimal energy expenditure, the latter enables controlling and fine-tuning by means of local and regional regulatory systems and also, hormonal control. The paracellular pathway is driven by an electrochemical gradient and realized in principal by the tight junction (TJ), a supramolecular organization of membrane-bound proteins and their adaptor and scaffolding proteins. TJ determinants are claudins (CLDN), a family of membrane spanning proteins that generate a barrier or a pore between two adjacent epithelial cells. Many insights into molecular mechanisms of Mg2+ handling have been achieved by the identification of alterations and mutations in human genes which cause disorders of paracellular Mg2+ pathways (CLDN10, CLDN14, CLDN16, CLDN19). Also, in the distal convoluted tubule, a basolateral protein, CNNM2, causes if mutated, familial dominant and also recessive renal Mg2+ wasting, albeit its true function has not been clarified yet, but is assumed to play a key role in the transcellular pathway. Moreover, mutations in human genes that are involved in regulating these proteins directly or indirectly cause, if mutated human diseases, mostly in combination with comorbidities as diabetes, cystic renal disease, or metabolic abnormalities. Generation and characterization of animal models harboring the corresponding mutations have further contributed to the elucidation of physiology and pathophysiology of Mg2+ disorders. Finally, high-end crystallization techniques allow understanding of Mg2+ handling in more detail. As this field is rapidly growing, we describe here the principles of physiology and pathophysiology of epithelial transport of renal Mg2+ homeostasis with emphasis on recently identified mechanisms involved.

Crystal structure of cystathionine ß-synthase from honeybee Apis mellifera.

Cystathionine ß-synthase (CBS), the key enzyme in the transsulfuration pathway, links methionine metabolism to the biosynthesis of cellular redox controlling molecules. CBS catalyzes the pyridoxal-5'-phosphate-dependent condensation of serine and homocysteine to form cystathionine, which is subsequently converted into cysteine. Besides maintaining cellular sulfur amino acid homeostasis, CBS also catalyzes multiple hydrogen sulfide-generating reactions using cysteine and homocysteine as substrates. In mammals, CBS is activated by S-adenosylmethionine (AdoMet), where it can adopt two different conformations (basal and activated), but exists as a unique highly active species in fruit fly Drosophila melanogaster. Here we present the crystal structure of CBS from honeybey Apis mellifera, which shows a constitutively active dimeric species and let explain why the enzyme is not allosterically regulated by AdoMet. In addition, comparison of available CBS structures unveils a substrate-induced closure of the catalytic cavity, which in humans is affected by the AdoMet-dependent regulation and likely impaired by the homocystinuria causing mutation T191M.

Potential Pharmacological Chaperones for Cystathionine Beta-Synthase-Deficient Homocystinuria.

Classical homocystinuria (HCU) is the most common loss-of-function inborn error of sulfur amino acid metabolism. HCU is caused by a deficiency in enzymatic degradation of homocysteine, a toxic intermediate of methionine transformation to cysteine, chiefly due to missense mutations in the cystathionine beta-synthase (CBS) gene. As with many other inherited disorders, the pathogenic mutations do not target key catalytic residues, but rather introduce structural perturbations leading to an enhanced tendency of the mutant CBS to misfold and either to form nonfunctional aggregates or to undergo proteasome-dependent degradation. Correction of CBS misfolding would represent an alternative therapeutic approach for HCU. In this review, we summarize the complex nature of CBS, its multi-domain architecture, the interplay between the three cofactors required for CBS function [heme, pyridoxal-5'-phosphate (PLP), and S-adenosylmethionine (SAM)], as well as the intricate allosteric regulatory mechanism only recently understood, thanks to advances in CBS crystallography. While roughly half of the patients respond to treatment with a PLP precursor pyridoxine, many studies suggested usefulness of small chemicals, such as chemical and pharmacological chaperones or proteasome inhibitors, rescuing mutant CBS activity in cellular and animal models of HCU. Non-specific chemical chaperones and proteasome inhibitors assist in mutant CBS folding process and/or prevent its rapid degradation, thus resulting in increased steady-state levels of the enzyme and CBS activity. Recent interest in the field and available structural information will hopefully yield CBS-specific compounds, by using high-throughput screening and computational modeling of novel ligands, improving folding, stability, and activity of CBS mutants.

Structural Basis of the Oncogenic Interaction of Phosphatase PRL-1 with the Magnesium Transporter CNNM2.

Phosphatases of regenerating liver (PRLs), the most oncogenic of all protein-tyrosine phosphatases (PTPs), play a critical role in metastatic progression of cancers. Recent findings established a new paradigm by uncovering that their association with magnesium transporters of the cyclin M (CNNM) family causes a rise in intracellular magnesium levels that promote oncogenic transformation. Recently, however, essential roles for regulation of the circadian rhythm and reproduction of the CNNM family have been highlighted. Here, we describe the crystal structure of PRL-1 in complex with the Bateman module of CNNM2 (CNNM2BAT), which consists of two cystathionine ß-synthase (CBS) domains (IPR000664) and represents an intracellular regulatory module of the transporter. The structure reveals a heterotetrameric association, consisting of a disc-like homodimer of CNNM2BAT bound to two independent PRL-1 molecules, each one located at opposite tips of the disc. The structure highlights the key role played by Asp-558 at the extended loop of the CBS2 motif of CNNM2 in maintaining the association between the two proteins and proves that the interaction between CNNM2 and PRL-1 occurs via the catalytic domain of the phosphatase. Our data shed new light on the structural basis underlying the interaction between PRL phosphatases and CNNM transporters and provides a hypothesis about the molecular mechanism by which PRL-1, upon binding to CNNM2, might increase the intracellular concentration of Mg2+ thereby contributing to tumor progression and metastasis. The availability of this structure sets the basis for the rational design of compounds modulating PRL-1 and CNNM2 activities.