Interfacial amino acids support Spa47 oligomerization and shigella type three secretion system activation

Like many Gram-negative pathogens, Shigella rely on a type three secretion system (T3SS) for injection of effector proteins directly into eukaryotic host cells to initiate and sustain infection. Protein secretion through the needle-like type three secretion apparatus (T3SA) requires ATP hydrolysis by the T3SS ATPase Spa47, making it a likely target for in vivo regulation of T3SS activity and an attractive target for small molecule therapeutics against shigellosis. Here, we developed a model of an activated Spa47 homo-hexamer, identifying two distinct regions at each protomer interface that we hypothesized to provide intermolecular interactions supporting Spa47 oligomerization and enzymatic activation. Mutational analysis and a series of high-resolution crystal structures confirm the importance of these residues, as many of the engineered mutants are unable to form oligomers and efficiently hydrolyze ATP in vitro. Furthermore, in vivo evaluation of Shigella virulence phenotype uncovered a strong correlation between T3SS effector protein secretion, host cell membrane disruption, and cellular invasion by the tested mutant strains, suggesting that perturbation of the identified interfacial residues/interactions influences Spa47 activity through preventing oligomer formation, which in turn regulates Shigella virulence. The most impactful mutations are observed within the conserved Site 2 interface where the native residues support oligomerization and likely contribute to a complex hydrogen bonding network that organizes the active site and supports catalysis. The critical reliance on these conserved residues suggests that aspects of T3SS regulation may also be conserved, providing promise for the development of a cross-species therapeutic that broadly targets T3SS ATPase oligomerization and activation.

Anti-Vel alloimmunization and severe hemolytic disease of the fetus and newborn

Only rare cases of anti-Vel-associated mild-to-moderate hemolytic disease of the fetus and newborn have been previously reported. No case of fetal anemia requiring prenatal therapy has been noted to date. We report such a case recently encountered at our Fetal Center. Strategies are discussed for managing pregnancy complicated with alloimmunization to an antibody to a high-prevalence antigen, including sources of red blood cells for intrauterine transfusions. Only rare cases of anti-Vel–associated mild-to-moderate hemolytic disease of the fetus and newborn have been previously reported. No case of fetal anemia requiring prenatal therapy has been noted to date. We report such a case recently encountered at our Fetal Center. Strategies are discussed for managing pregnancy complicated with alloimmunization to an antibody to a high-prevalence antigen, including sources of red blood cells for intrauterine transfusions.

A YopH PTP1B Chimera Shows the Importance of the WPD-Loop Sequence to the Activity, Structure, and Dynamics of Protein Tyrosine Phosphatases

To study factors that affect WPD-loop motion in protein tyrosine phosphatases (PTPs), a chimera of PTP1B and YopH was created by transposing the WPD loop from PTP1B to YopH. Several subsequent mutations proved to be necessary to obtain a soluble, active enzyme. That chimera, termed chimera 3, retains productive WPD-loop motions and general acid catalysis with a pH dependency similar to that of the native enzymes. Kinetic isotope effects show the mechanism and transition state for phosphoryl transfer are unaltered. Catalysis of the chimera is slower than that of either of its parent enzymes, although its rate is comparable to those of most native PTPs. X-ray crystallography and nuclear magnetic resonance were used to probe the structure and dynamics of chimera 3. The chimera's structure was found to sample an unproductive hyper-open conformation of its WPD loop, a geometry that has not been observed in either of the parents or in other native PTPs. The reduced catalytic rate is attributed to the protein's sampling of this conformation in solution, reducing the fraction in the catalytically productive loop-closed conformation.

Structure of frequency-interacting RNA helicase from Neurospora crassa reveals high flexibility in a domain critical for circadian rhythm and RNA surveillance

The FRH (frequency-interacting RNA helicase) protein is the Neurospora crassa homolog of yeast Mtr4, an essential RNA helicase that plays a central role in RNA metabolism as an activator of the nuclear RNA exosome. FRH is also a required component of the circadian clock, mediating protein interactions that result in the rhythmic repression of gene expression. Here we show that FRH unwinds RNA substrates in vitro with a kinetic profile similar to Mtr4, indicating that while FRH has acquired additional functionality, its core helicase function remains intact. In contrast with the earlier FRH structures, a new crystal form of FRH results in an ATP binding site that is undisturbed by crystal contacts and adopts a conformation consistent with nucleotide binding and hydrolysis. Strikingly, this new FRH structure adopts an arch domain conformation that is dramatically altered from previous structures. Comparison of the existing FRH structures reveals conserved hinge points that appear to facilitate arch motion. Regions in the arch have been previously shown to mediate a variety of protein-protein interactions critical for RNA surveillance and circadian clock functions. The conformational changes highlighted in the FRH structures provide a platform for investigating the relationship between arch dynamics and Mtr4/FRH function.

Structural and Biochemical Characterization of Spa47 Provides Mechanistic Insight into Type III Secretion System ATPase Activation and Shigella Virulence Regulation

Like many Gram-negative pathogens, Shigella rely on a complex type III secretion system (T3SS) to inject effector proteins into host cells, take over host functions, and ultimately establish infection. Despite these critical roles, the energetics and regulatory mechanisms controlling the T3SS and pathogen virulence remain largely unclear. In this study, we present a series of high resolution crystal structures of Spa47 and use the structures to model an activated Spa47 oligomer, finding that ATP hydrolysis may be supported by specific side chain contributions from adjacent protomers within the complex. Follow-up mutagenesis experiments targeting the predicted active site residues validate the oligomeric model and determined that each of the tested residues are essential for Spa47 ATPase activity, although they are not directly responsible for stable oligomer formation. Although N-terminal domain truncation was necessary for crystal formation, it resulted in strictly monomeric Spa47 that is unable to hydrolyze ATP, despite maintaining the canonical ATPase core structure and active site residues. Coupled with studies of ATPase inactive full-length Spa47 point mutants, we find that Spa47 oligomerization and ATP hydrolysis are needed for complete T3SS apparatus formation, a proper translocator secretion profile, and Shigella virulence. This work represents the first structure-function characterization of Spa47, uniquely complementing the multitude of included Shigella T3SS phenotype assays and providing a more complete understanding of T3SS ATPase-mediated pathogen virulence. Additionally, these findings provide a strong platform for follow-up studies evaluating regulation of Spa47 oligomerization in vivo as a much needed means of treating and perhaps preventing shigellosis.

Factors associated with chloroquine-induced retinopathy in rheumatic diseases

Antimalarials are very useful drugs in the treatment of various rheumatic diseases. One of their main side effects is ocular toxicity, specifically retinopathy. Our objective was to identify risk factors associated with chloroquine retinopathy. A single, trained evaluator reviewed patient records with rheumatic diseases. They were taking chloroquine and identified by the ophthalmologydepartment as having retinopathy during their routine eye evaluation. These cases were classified according to clinical evaluation, visual fields and fluorangiographic study. Up to four controls were selected for each case, matched by age, gender, diagnosisand similar time on chloroquine.In all, 34 variableswere studied, among these: weight, age, disease duration, keratopathy, total cumulative dose (TCD), mean daily dose (MDD), lean body weight adjusted daily dose (LBWDD) and laboratory tests. Descriptive and inferential statistics comparing cases and controls in all patients and subgroup analysis were carried out. Significance was set at the 0.05 level. Odds ratio and 95% confidence intervals were calculated. Sixteen cases of chloroquine retinopathy were identified, eight patients with rheumatoid arthritis (RA), seven with systemic lupus erythematosus (SLE) and one with dermatomyositis. All were female. Mean age was 47.3 + 12.2 years; weight 59.5 + 10.7 kg; disease duration 12.8 + 6.0 years; time on chloroquine 54.1 + 27.8 (min-max: 30-197) months. There was a significant difference in the following variables in all patients: MDD 212.3 + 52.6 versus 170 + 51.3, p 0.009; and LBWDD 5 + 1 versus 4.2 + 1.5, p 0.03, for cases and controls, respectively. In subgroup analysis the MDD remained significantly different (235.5 + 45.8 versus 169.7 + 46.l, p 0.004) only in RA, whereas LBWDD was different both in SLE and RA. Keratopathy increased the risk for retinopathy: OR, 95% CI: 5, 1.4-l7.6, p 0.01. In conclusion, in accordance with previous studies, the MDD, LBWDD and keratopathy were risk factors associated with chloroquine retinopathy. Periodic ophthalmologic evaluations are mandatory.

Biochemistry and regulation of the protein arginine methyltransferases (PRMTs)

Many key cellular processes can be regulated by the seemingly simple addition of one, or two, methyl groups to arginine residues by the nine known mammalian protein arginine methyltransferases (PRMTs). The impact that arginine methylation has on cellular well-being is highlighted by the ever growing evidence linking PRMT dysregulation to disease states, which has marked the PRMTs as prominent pharmacological targets. This review is meant to orient the reader with respect to the structural features of the PRMTs that account for catalytic activity, as well as provide a framework for understanding how these enzymes are regulated. An overview of what we understand about substrate recognition and binding is provided. Control of product specificity and enzyme processivity are introduced as necessary but flexible features of the PRMTs. Precise control of PRMT activity is a critical component to eukaryotic cell health, especially given that an arginine demethylase has not been identified. We therefore conclude the review with a comprehensive discussion of how protein arginine methylation is regulated.

Redox Control of Protein Arginine Methyltransferase 1 (PRMT1) Activity

Elevated levels of asymmetric dimethylarginine (ADMA) correlate with risk factors for cardiovascular disease. ADMA is generated by the catabolism of proteins methylated on arginine residues by protein arginine methyltransferases (PRMTs) and is degraded by dimethylarginine dimethylaminohydrolase. Reports have shown that dimethylarginine dimethylaminohydrolase activity is down-regulated and PRMT1 protein expression is up-regulated under oxidative stress conditions, leading many to conclude that ADMA accumulation occurs via increased synthesis by PRMTs and decreased degradation. However, we now report that the methyltransferase activity of PRMT1, the major PRMT isoform in humans, is impaired under oxidative conditions. Oxidized PRMT1 displays decreased activity, which can be rescued by reduction. This oxidation event involves one or more cysteine residues that become oxidized to sulfenic acid (-SOH). We demonstrate a hydrogen peroxide concentration-dependent inhibition of PRMT1 activity that is readily reversed under physiological H2O2 concentrations. Our results challenge the unilateral view that increased PRMT1 expression necessarily results in increased ADMA synthesis and demonstrate that enzymatic activity can be regulated in a redox-sensitive manner.

Myelin oligodendrocyte glycoprotein antibodies in pathologically proven multiple sclerosis: frequency, stability and clinicopathologic correlations

Controversy exists regarding the pathogenic or predictive role of anti-myelin oligodendrocyte glycoprotein (MOG) antibodies in patients with multiple sclerosis (MS). Four immunopathological patterns (IP) have been recognized in early active MS lesions, suggesting heterogeneous pathogenic mechanisms. Whether MOG antibodies contribute to this pathological heterogeneity and potentially serve as biomarkers to identify specific pathological patterns is unknown. Here we report the frequencies of antibodies to human recombinant MOG (identified by Western blot and enzyme-linked immunoabsorbent assay (ELISA)) in patients with pathologically proven demyelinating disease, and investigate whether antibody status is associated with clinical course, HLA-DR2-genotype, IP or treatment response to plasmapheresis. The biopsy cohort consisted of 72 patients: 12 pattern I, 43 pattern II and 17 pattern III. No association was found between MOG antibody status and conversion to clinically definite MS, DR-2 status, IP or response to plasmapheresis. There was poor agreement between Western blot and ELISA (kappa = 0.07 for MOG IgM). Fluctuations in antibody seropositivity were seen for 3/4 patients tested serially by Western blot. This study does not support a pathologic pattern-specific role for MOG-antibodies. Variable MOG-antibody status on serial measurements, coupled with the lack of Western blot and ELISA correlations, raises concern regarding the use of MOG-antibody as an MS biomarker and underscores the need for methodological consensus.

Breastfeeding infants who were extremely low birth weight

OBJECTIVE

To compare the clinical effect of breastfeedings and bottle feedings in extremely low birth weight (ELBW) infants (birth weight </=800 g).

METHODS

A total of 12 ELBW infants (mean birth weight, 672 +/- 95 g; mean gestation, 26 +/- 2 weeks) served as their own controls in this prospective study comparing physiologic parameters during bottle and breastfeeding. The infants were put to breast the same week they began on bottle feedings of human milk or premature infant formula (mean gestation, 35 weeks). One breastfeeding and one bottle feeding were observed each day for 10 days. Pre- and postfeeding weights were measured, and oxygen saturation, respiratory rate, heart rate, and axillary temperature were monitored continuously and recorded every minute during feedings.

RESULTS

The infants demonstrated a higher oxygen saturation and a higher temperature during breastfeeding than during bottle feeding, and were less likely to desaturate to <90% oxygen during breastfeeding. Mean weight gain was greater during bottle feeding than during breastfeeding (31 vs 9 g).

CONCLUSIONS

Breastfeeding the ELBW infant is desirable from a standpoint of improved physiologic responses, but such practice requires breastfeeding support and possible supplementation to optimize weight gain.

Medical and social factors associated with cognitive outcome in individuals with myelomeningocele

The interrelationship between biological and social risk factors and cognitive outcome in individuals with myelomeningocele was examined. The Kaufman Brief Intelligence Test (K-BIT) was administered to 65 children and young adults, age range 4 to 29 during a recent clinic visit. Unshunted individuals had scores in the average range and individuals with uncomplicated hydrocephalus in the low-average range. Although the level of lesion was found to be most strongly associated with total K-BIT score, examination of subscores indicated that socioeconomic status was the factor most strongly associated with Vocabulary score. The importance of both social and biological factors in predicting cognitive outcome in this population is useful in planning intervention strategies.

Comparison of skin-to-skin contact with standard contact in low-birth-weight infants who are breast-fed

OBJECTIVE

To evaluate the effects of maternal-infant skin-to-skin contact (SSC) vs standard contact (SC) on low-birth-weight infants' physiological profile, maternal milk production, and duration of breast-feeding.

DESIGN

Prospective, randomized, interventional study with cohort followed up for 6 months after discharge from the hospital.

SETTING

Special care nursery with follow-up telephone calls after discharge from the hospital.

PATIENTS

Fifty infants, with birth weights less than 1500 g and whose mothers planned to breast-feed, randomized to 2 groups: SSC (experimental) and SC (control).

INTERVENTION

In the SSC group, infants were clothed in diaper and held upright between mothers' breasts; both mother and infant were covered with a blanket. In the SC group, infants were clothed, wrapped in blankets, and held cradled in mother's arms.

MAIN OUTCOME MEASURES

Infant physiological data, ie, oxygen saturation, heart rate, respiratory rate, and axillary temperature; maternal milk production; and duration of breast-feeding.

RESULTS

Oxygen saturation was higher during SSC than during SC (P < .001); 11% of the oxygen saturation recordings during SSC vs 24% during SC indicated the values less than 90% (P < .001). A more stable milk production was noted in the SSC group. No differences were noted in infant temperature, heart rate, or respiratory rate. Ninety percent of mothers in the SSC group vs 61% in the SC group continued breast-feeding for the duration of the infants' hospitalization (P < .05), and 50% in the SSC group vs 11% in the SC continued breast-feeding through 1 month after discharge (P < .01).

CONCLUSIONS

During SSC with their mothers, low-birth-weight infants maintain a higher oxygen saturation and are less likely to have desaturation to less than 90% oxygen than are infants exposed to SC. Mothers in the SSC group are more likely to continue breast-feeding until 1 month after discharge.

Parents' and pediatricians' views of individuals with meningomyelocele

The parents of 63 individuals with meningomyelocele completed a scale examining the effects of their child's disability on their family. Eighty-six pediatricians also completed the scale as they predicted parents would respond. Medical and psychosocial data were also obtained. The results showed the following: (1) A higher level lesion was associated with parental reports of a more negative impact on the family (p < .05), and (2) pediatricians predicted a more negative impact than was reported by the parents (p < .001). We conclude that pediatricians overestimate the negative effects while also underestimating the positive effects of the disability on the family.

[Anal neoplasms. Treatment with radiotherapy and exclusive chemotherapy]

We report preliminary results on treatment of anal carcinoma by radiotherapy and chemotherapy. Nine patients (mean age 64, 6 females) were treated with 5-fluorouracil and mitomycin C intravenously, associated to radiotherapy (3000 rads in 10 days). The lesion was located in the anal canal in 4 patients and at the anal margin in 5. Good response was observed in every patient with no evidence of recurrence during a 2 to 30 month follow up period (median 16). A greater number of patients and a longer follow up period is required to establish this as a valid alternative to abdomino-perineal surgery for the treatment of anal carcinoma.

[Volume, flow and respiratory muscle strength in mitral stenosis]

Pulmonary function and respiratory muscle strength was assessed in 20 patients with mitral stenosis uncomplicated by other illness. Pulmonary function was evaluated by spirometry, flow-volume curves, functional residual capacity (FRC) and total lung capacity (TLC). Respiratory muscle strength was evaluated by measurement of maximal static inspiratory and expiratory mouth pressure (PIM, PEM cmH2O) at FRC and TLC respectively. Spirometric, FRC and TLC average values were normal. The maximal expiratory flow rate at 50 and 25% of vital capacity were decreased to 49.5 and 38.3% from predicted values. The values of PIM and PEM in patients (-93 +/- 17; 128 +/- 32 cmH2O, respectively) were similar to those of 12 normal subjects studied at comparable lung volume. Our results were similar to previous reports. There was no evidence of decreased respiratory muscle force, probably because the patients nutritional status and cardiac output were normal.