Structural basis of the obligatory exchange mode of human neutral amino acid transporter ASCT2.

ASCT2 is an obligate exchanger of neutral amino acids, contributing to cellular amino acid homeostasis. ASCT2 belongs to the same family (SLC1) as Excitatory Amino Acid Transporters (EAATs) that concentrate glutamate in the cytosol. The mechanism that makes ASCT2 an exchanger rather than a concentrator remains enigmatic. Here, we employ cryo-electron microscopy and molecular dynamics simulations to elucidate the structural basis of the exchange mechanism of ASCT2. We establish that ASCT2 binds three Na+ ions per transported substrate and visits a state that likely acts as checkpoint in preventing Na+ ion leakage, both features shared with EAATs. However, in contrast to EAATs, ASCT2 retains one Na+ ion even under Na+-depleted conditions. We demonstrate that ASCT2 cannot undergo the structural transition in TM7 that is essential for the concentrative transport cycle of EAATs. This structural rigidity and the high-affinity Na+ binding site effectively confine ASCT2 to an exchange mode.

Ectodermal disturbance in development shared by anorexia and schizophrenia may reflect neurodevelopmental abnormalities.

Minor physical abnormalities (MPA) are subtle dysmorphic features of bodily structures that have little or no impact on function. Most MPA develop during the first gestational trimester and are considered as important indicators of neuroectodermal deficiencies emerging during early brain development. A higher frequency of MPA was confirmed in schizophrenia patients and their relatives, when compared to controls. These findings are consistent with the neurodevelopmental model of schizophrenia. A neurodevelopmental component amongst other risk factors has also been recently proposed for anorexia nervosa (AN). The current study aimed to assess MPA frequency in adolescent inpatients with either schizophrenia spectrum disorders (SSD) or AN as compared to healthy controls (HC). The Waldrop Scale was used for assessing MPA. The mean MPA total score and mean head subscore was significantly higher in both test groups than in HC. There were no statistically significant differences between SSD and AN groups. The MPA profile (not frequency) was similar in all three groups. This finding is consistent both with widely acknowledged neurodevelopmental schizophrenia hypothesis as well as with more recent neurodevelopmental model of AN. Nevertheless, the findings should not be overgeneralized and further studies are warranted.

What exactly is catatonia in children and adolescents. / Czym jest katatonia u dzieci i mlodziezy.

The current study is a review of the literature on catatonia syndrome with focus on children and adolescent's specificity. Previous catatonia conceptualizations were significantly modified in the newest classification systems. Catatonia may be considered either a separate syndrome or a specifier of the course of other psychiatric disorders. Although diagnostic criteria for children and adolescent do not differ from those for adults, the clinical presentation and course may not be the same. In this age group relatively common are somatic conditions taking the form of catatonia. There is agrowing body of literature focused on catatonia in the course of pervasive developmental disorder. On the other hand, pervasive refusal syndrome and lethal catatonia are discussed in the literature, but they are not present in the classification systems. In the current paper basic treatment guidelines were also described. First-line treatment is the use of benzodiazepines and electroconvulsive therapy. The diagnosis and treatmentof catatonia is of great practical importance. While improper diagnosis and non-optimal treatment may have fatal consequences, in the case of proper diagnosis an effective treatment may be administered.

Molecular mechanism of vSGLT inhibition by gneyulin reveals antiseptic properties against multidrug-resistant gram-negative bacteria.

Faced with the worldwide spread of multidrug-resistant (MDR) bacterial strains, together with a lack of any appropriate treatment, urgent steps to combat infectious diseases should be taken. Usually, bacterial components are studied to understand, by analogy, the functioning of human proteins. However, molecular data from bacteria gathered over the past decades provide a sound basis for the search for novel approaches in medical care. With this current work, we want to direct attention to inhibition of the vSGLT glucose transporter from Vibrio parahaemolyticus belonging to the sodium solute symporter (SSS) family, to block sugar transport into the bacterial cell and, as a consequence, to limit its growth. Potential bacteriostatic properties can be drawn from commercially available drugs developed for human diseases. This goal can also be reached with natural components from traditional herbal medicine. The presented data from the numerical analysis of 44 known inhibitors of sodium glucose symporters shed light on potential novel approaches in fighting Gram-negative multidrug-resistant microorganisms. Graphical abstract Molecular view on vSGLT channel inhibition by gneyulin B, the compound of natural origin.

Mutations resulting in the formation of hyperactive complement convertases support cytocidal effect of anti-CD20 immunotherapeutics.

Anti-CD20 monoclonal antibodies (mAbs) rituximab and ofatumumab are potent activators of the classical complement pathway, and have been approved for the treatment of B-cell malignancies. However, complement exhaustion and overexpression of complement inhibitors by cancer cells diminish their therapeutic potential. The strategies of targeting membrane complement inhibitors by function-blocking antibodies and the supplementation with fresh frozen plasma have been proposed to overcome tumour cell resistance. We present a novel approach, which utilizes gain-of-function variants of complement factor B (FB), a component of alternative C3/C5 convertases, which augment mAb-activated reactions through a positive feedback mechanism called an amplification loop. If complement concentration is limited, an addition of quadruple gain-of-function FB mutant p.D279G p.F286L p.K323E p.Y363A (or selected single mutants) results in significantly increased complement-mediated lysis of ofatumumab-resistant tumour cells, as well as the complete lysis of moderately sensitive cells. Importantly, this effect cannot be achieved by further increasing ofatumumab concentration. Potentiation of cytotoxic effect towards moderately sensitive cells was less apparent at physiological serum concentration. However, an addition of hyperactive FB could compensate the loss of cytotoxic potential of serum collected from the NHL and CLL patients after infusion of rituximab. Residual levels of rituximab in such sera, in combination with added FB, were able to efficiently lyse tumour cells. We suggest that the administration of gain-of-function variants of FB can restore cytotoxic potential of complement-exhausted serum and maximize the therapeutic effect of circulating anti-CD20 mAbs.

Gain of function mutant of complement factor B K323E mimics pathogenic C3NeF autoantibodies in convertase assays.

Complement convertases are enzymatic complexes, which play a critical role in propagation and amplification of the complement cascade. Under physiological conditions, convertases decay shortly after being formed in either spontaneous or inhibitor-driven process. Prolongation of their half-life by C3NeF autoantibodies that prevent convertase dissociation results in pathogenic condition often manifested by renal diseases. However, the diagnosis of convertase abnormalities is difficult due to the labile nature of these enzymes and low credibility of existing methods. Only recently, two-step functional assays employing C5-depleted serum or C5 inhibitors were introduced. Their advantage is convertase formation in the physiological milieu of whole serum and the drawback is inter-assay variability due to variations in rabbit erythrocytes used for the haemolysis-based readout. Abovementioned problems demand the application of the internal standard in each experiment. Obtaining a defined preparation of autoantibodies is complicated due to ethical and practical considerations. We found that recombinant, his-tagged factor B (fB) variant K323E retains full hemolytic activity and possess the ability to form convertases with prolonged half-life either in fB-depleted serum or when mixed with normal human serum. Such dominant character of K323E mutation allows using recombinant protein as a reference in functional convertase assays, not limited to these using rabbit erythrocytes. Additionally, our results demonstrate that gain of function mutations in complement components mimic the phenotype of C3NeF. Hence, patients with such "genetic C3NeF" would not benefit from B-cell depletion (e.g. by rituximab) and therefore should be properly diagnosed in order to choose suitable therapeutic intervention.

Medulloblastoma: molecular pathways and histopathological classification.

Malignant brain tumors are the leading cause of cancer death among pediatric patients, and medulloblastoma constitutes 20% of them. Currently, the treatment is risk-adapted. Maximum surgical resection is recommended, always followed by chemotherapy and neuroaxis radiotherapy. In spite of the improving survival rate, survivors succumb to treatment-induced side effects. To reduce toxic effects, molecular-targeted treatment is proposed. Medulloblastoma research is very robust, and new articles on the subject are published daily. In the current review we have tried to bring together molecular pathophysiology of the neoplasm and current pathological classification, thus making an effort to relate tumor biology and the histological picture.

Central nervous system haemorrhage causing early death in acute promyelocytic leukaemia.

Acute promyelocytic leukaemia (APL) is a rare type of paediatric leukaemia characterised by a specific genetic mutation and life-threatening coagulopathy. The discovery of all-trans retinoic acid (ATRA), which acts directly on promyelocytic locus-retinoic acid receptor α (PML-RARα) gene product, brought a revolution to the therapy of this disorder. Unfortunately, despite an improvement in the complete remission rate, the early death (ED) rate has not changed significantly, and the haemorrhages remain a major problem. The most common bleeding site, which accounts for about 65-80% of haemorrhages, is the central nervous system. Second in line are pulmonary haemorrhages (32%), while gastrointestinal bleedings are relatively rare. Haemorrhages result from thrombocytopaenia, disseminated intravascular coagulopathy (DIC), and systemic fibrinolysis. Herein we present a boy aged one year and nine months with APL. The patient was not eligible for ATRA administration due to poor clinical condition. He developed bleeding diathesis that presented as disseminated intravascular coagulation (DIC) and led to intracranial haemorrhage, which resulted in the patient's death.

Effect of methylprednisolone pulse therapy with and without alendronate on biochemical markers of bone turnover in patients with Graves' ophthalmopathy.

INTRODUCTION:  Immunosuppression with glucocorticoids is the method of choice in the treatment of active Graves' ophthalmopathy (GO). However, glucocorticoid therapy may have side effects, among others, it affects bone metabolism. OBJECTIVES:  The aim of the study was to compare the effect of methylprednisolone pulse therapy (MPPT) with and without alendronate on bone turnover markers in patients with GO with normal and reduced bone mineral density (BMD). PATIENTS AND METHODS:  The study included 53 patients with GO and 20 sex- and age­matched healthy controls. Twenty patients with normal BMD (17 women, 3 men, aged 45 ±1.0 years) received only MPPT (8 g intravenously during 4 weeks). The remaining patients, with reduced BMD, were randomly assigned either to MPPT without alendronate (10 women, 2 men, aged 47 ±1.0 years) or MPPT with alendronate (18 women, 3 men, aged 47 ±1.0 years). BMD of the lumbar spine and femoral neck was assessed using dual energy X­ray absorptiometry  (DEXA) before treatment. The markers of bone formation (serum osteocalcin, carboxyterminal propeptide of type I collagen [PICP], alkaline phospatase) and the markers of bone resorption (serum carboxyterminal telopeptide of type I collagen [ICTP], cross­linked C­terminal telopeptide of type I collagen [CTX], serum calcium [Ca] and potassium [P], as well as urinary excretion of deoxypyridinoline, Ca, and P) were determined before and after treatment. RESULTS:  MPPT caused a decrease in bone formation markers and an increase in some bone resorption markers. MPPT with alendronate decreased bone formation and bone resorption markers. CONCLUSIONS:  A negative effect of MPPT on bone turnover is observed both in patients with GO with normal and with reduced BMD. Simultaneous use of MPPT and alendronate in patients with GO and reduced BMD suppresses bone resorption caused by methylprednisolone.