ATP sensitive bi-quinoline activator of the AMP-activated protein kinase

The AMP-activated protein kinase (AMPK) regulates cellular and whole-body energy balance in response to changes in adenylate charge and hormonal signals. Activation of AMPK in tissues such as skeletal muscle and liver reverses many of the metabolic defects associated with obesity and Type 2 diabetes. Here we report a bi-quinoline (JJO-1) that allosterically activates all AMPK αβγ isoforms in vitro except complexes containing the γ3 subunit. JJO-1 does not directly activate the autoinhibited α subunit kinase domain and differs among other known direct activators of AMPK in that allosteric activation occurs only at low ATP concentrations, and is not influenced by either mutation of the γ subunit adenylate-nucleotide binding sites or deletion of the β subunit carbohydrate-binding module. Our findings indicate that AMPK has multiple modes of allosteric activation that may be exploited to design isoform-specific activators as potential therapeutics for metabolic diseases.     

Characterisation of Peptide Microarrays for Studying Antibody-Antigen Binding Using Surface Plasmon Resonance Imagery

Background

Non-specific binding to biosensor surfaces is a major obstacle to quantitative analysis of selective retention of analytes at immobilized target molecules. Although a range of chemical antifouling monolayers has been developed to address this problem, many macromolecular interactions still remain refractory to analysis due to the prevalent high degree of non-specific binding. We describe how we use the dynamic process of the formation of self assembling monolayers and optimise physical and chemical properties thus reducing considerably non-specific binding and allowing analysis of specific binding of analytes to immobilized target molecules.

Methodology/Principal Findings

We illustrate this approach by the production of specific protein arrays for the analysis of interactions between the 65kDa isoform of human glutamate decarboxylase (GAD65) and a human monoclonal antibody. Our data illustrate that we have effectively eliminated non-specific interactions with the surface containing the immobilised GAD65 molecules. The findings have several implications. First, this approach obviates the dubious process of background subtraction and gives access to more accurate kinetic and equilibrium values that are no longer contaminated by multiphase non-specific binding. Second, an enhanced signal to noise ratio increases not only the sensitivity but also confidence in the use of SPR to generate kinetic constants that may then be inserted into van''t Hoff type analyses to provide comparative ΔG, ΔS and ΔH values, making this an efficient, rapid and competitive alternative to ITC measurements used in drug and macromolecular-interaction mechanistic studies. Third, the accuracy of the measurements allows the application of more intricate interaction models than simple Langmuir monophasic binding.

Conclusions

The detection and measurement of antibody binding by the type 1 diabetes autoantigen GAD65 represents an example of an antibody-antigen interaction where good structural, mechanistic and immunological data are available. Using SPRi we were able to characterise the kinetics of the interaction in greater detail than ELISA/RIA methods. Furthermore, our data indicate that SPRi is well suited to a multiplexed immunoassay using GAD65 proteins, and may be applicable to other biomarkers.     

Structural Mechanisms of Inactivation in Scabies Mite Serine Protease Paralogues

The scabies mite (Sarcoptes scabiei) is a parasite responsible for major morbidity in disadvantaged communities and immuno-compromised patients worldwide. In addition to the physical discomfort caused by the disease, scabies infestations facilitate infection by Streptococcal species via skin lesions, resulting in a high prevalence of rheumatic fever/heart disease in affected communities. The scabies mite produces 33 proteins that are closely related to those in the dust mite group 3 allergen and belong to the S1-like protease family (chymotrypsin-like). However, all but one of these molecules contain mutations in the conserved active-site catalytic triad that are predicted to render them catalytically inactive. These molecules are thus termed scabies mite inactivated protease paralogues (SMIPPs). The precise function of SMIPPs is unclear; however, it has been suggested that these proteins might function by binding and protecting target substrates from cleavage by host immune proteases, thus preventing the host from mounting an effective immune challenge. In order to begin to understand the structural basis for SMIPP function, we solved the crystal structures of SMIPP-S-I1 and SMIPP-S-D1 at 1.85 Å and 2.0 Å resolution, respectively. Both structures adopt the characteristic serine protease fold, albeit with large structural variations over much of the molecule. In both structures, mutations in the catalytic triad together with occlusion of the S1 subsite by a conserved Tyr200 residue is predicted to block substrate ingress. Accordingly, we show that both proteases lack catalytic function. Attempts to restore function (via site-directed mutagenesis of catalytic residues as well as Tyr200) were unsuccessful. Taken together, these data suggest that SMIPPs have lost the ability to bind substrates in a classical “canonical” fashion, and instead have evolved alternative functions in the lifecycle of the scabies mite.     

The X-Ray Crystal Structure of Escherichia coli Succinic Semialdehyde Dehydrogenase; Structural Insights into NADP+/Enzyme Interactions

Background

In mammals succinic semialdehyde dehydrogenase (SSADH) plays an essential role in the metabolism of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) to succinic acid (SA). Deficiency of SSADH in humans results in elevated levels of GABA and γ-Hydroxybutyric acid (GHB), which leads to psychomotor retardation, muscular hypotonia, non-progressive ataxia and seizures. In Escherichia coli, two genetically distinct forms of SSADHs had been described that are essential for preventing accumulation of toxic levels of succinic semialdehyde (SSA) in cells.

Methodology/Principal Findings

Here we structurally characterise SSADH encoded by the E coli gabD gene by X-ray crystallographic studies and compare these data with the structure of human SSADH. In the E. coli SSADH structure, electron density for the complete NADP⁺ cofactor in the binding sites is clearly evident; these data in particular revealing how the nicotinamide ring of the cofactor is positioned in each active site.

Conclusions/Significance

Our structural data suggest that a deletion of three amino acids in E. coli SSADH permits this enzyme to use NADP⁺, whereas in contrast the human enzyme utilises NAD⁺. Furthermore, the structure of E. coli SSADH gives additional insight into human mutations that result in disease.     

An overview of the serpin superfamily

Serpins are a broadly distributed family of protease inhibitors that use a conformational change to inhibit target enzymes. They are central in controlling many important proteolytic cascades, including the mammalian coagulation pathways. Serpins are conformationally labile and many of the disease-linked mutations of serpins result in misfolding or in pathogenic, inactive polymers.     

Evaluation of multiple micronutrient supplementation and medium-quantity lipid-based nutrient supplementation in pregnancy on child development in rural Niger: A secondary analysis of a cluster randomized controlled trial

BackgroundIt is estimated that over 250 million children under 5 years of age in low- and middle-income countries (LMICs) do not reach their full developmental potential. Poor maternal diet, anemia, and micronutrient deficiencies during pregnancy are associated with suboptimal neurodevelopmental outcomes in children. However, the effect of prenatal macronutrient and micronutrient supplementation on child development in LMIC settings remains unclear due to limited evidence from randomized trials.Methods and findingsWe conducted a 3-arm cluster-randomized trial (n = 53 clusters) that evaluated the efficacy of (1) prenatal multiple micronutrient supplementation (MMS; n = 18 clusters) and (2) lipid-based nutrient supplementation (LNS; n = 18 clusters) as compared to (3) routine iron–folic acid (IFA) supplementation (n = 17 clusters) among pregnant women in the rural district of Madarounfa, Niger, from March 2015 to August 2019 (ClinicalTrials.gov identifier {"type":"clinical-trial","attrs":{"text":"NCT02145000","term_id":"NCT02145000"}}NCT02145000). Children were followed until 2 years of age, and the Bayley Scales of Infant and Toddler Development III (BSID-III) were administered to children every 3 months from 6 to 24 months of age. Maternal report of WHO gross motor milestone achievement was assessed monthly from 3 to 24 months of age. An intention-to-treat analysis was followed. Child BSID-III data were available for 559, 492, and 581 singleton children in the MMS, LNS, and IFA groups, respectively. Child WHO motor milestone data were available for 691, 781, and 753 singleton children in the MMS, LNS, and IFA groups, respectively. Prenatal MMS had no effect on child BSID-III cognitive (standardized mean difference [SMD]: 0.21; 95% CI: −0.20, 0.62; p = 0.32), language (SMD: 0.16; 95% CI: −0.30, 0.61; p = 0.50) or motor scores (SMD: 0.18; 95% CI: −0.39, 0.74; p = 0.54) or on time to achievement of the WHO gross motor milestones as compared to IFA. Prenatal LNS had no effect on child BSID-III cognitive (SMD: 0.17; 95% CI: −0.15, 0.49; p = 0.29), language (SMD: 0.11; 95% CI: −0.22, 0.44; p = 0.53) or motor scores (SMD: −0.04; 95% CI: −0.46, 0.37; p = 0.85) at the 24-month endline visit as compared to IFA. However, the trajectory of BSID-III cognitive scores during the first 2 years of life differed between the groups with children in the LNS group having higher cognitive scores at 18 and 21 months (approximately 0.35 SD) as compared to the IFA group (p-value for difference in trajectory <0.001). Children whose mothers received LNS also had earlier achievement of sitting alone (hazard ratio [HR]: 1.57; 95% CI: 1.10 to 2.24; p = 0.01) and walking alone (1.52; 95% CI: 1.14 to 2.03; p = 0.004) as compared to IFA, but there was no effect on time to achievement of other motor milestones. A limitation of our study is that we assessed child development up to 2 years of age, and, therefore, we may have not captured effects that are easier to detect or emerge at older ages.ConclusionsThere was no benefit of prenatal MMS on child development outcomes up to 2 years of age as compared to IFA. There was evidence of an apparent positive effect of prenatal LNS on cognitive development trajectory and time to achievement of selected gross motor milestones.Trial registrationClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT02145000","term_id":"NCT02145000"}}NCT02145000.

Christopher R. Sudfeld and colleagues evaluate the benefit of multiple micronutrient supplementation and medium‐quantity lipid‐based nutrient supplementation in pregnancy on child development in rural Niger.     

Immunogenicity of an oral rotavirus vaccine administered with prenatal nutritional support in Niger: A cluster randomized clinical trial

BackgroundNutritional status may play a role in infant immune development. To identify potential boosters of immunogenicity in low-income countries where oral vaccine efficacy is low, we tested the effect of prenatal nutritional supplementation on immune response to 3 doses of a live oral rotavirus vaccine.Methods and findingsWe nested a cluster randomized trial within a double-blind, placebo-controlled randomized efficacy trial to assess the effect of 3 prenatal nutritional supplements (lipid-based nutrient supplement [LNS], multiple micronutrient supplement [MMS], or iron–folic acid [IFA]) on infant immune response (n = 53 villages and 1,525 infants with valid serology results: 794 in the vaccine group and 731 in the placebo group). From September 2015 to February 2017, participating women received prenatal nutrient supplement during pregnancy. Eligible infants were then randomized to receive 3 doses of an oral rotavirus vaccine or placebo at 6–8 weeks of age (mean age: 6.3 weeks, 50% female). Infant sera (pre-Dose 1 and 28 days post-Dose 3) were analyzed for anti-rotavirus immunoglobulin A (IgA) using enzyme-linked immunosorbent assay (ELISA). The primary immunogenicity end point, seroconversion defined as ≥3-fold increase in IgA, was compared in vaccinated infants among the 3 supplement groups and between vaccine/placebo groups using mixed model analysis of variance procedures. Seroconversion did not differ by supplementation group (41.1% (94/229) with LNS vs. 39.1% (102/261) with multiple micronutrients (MMN) vs. 38.8% (118/304) with IFA, p = 0.91). Overall, 39.6% (n = 314/794) of infants who received vaccine seroconverted, compared to 29.0% (n = 212/731) of infants who received placebo (relative risk [RR]: 1.36; 95% confidence interval [CI]: 1.18, 1.57, p < 0.001). This study was conducted in a high rotavirus transmission setting. Study limitations include the absence of an immune correlate of protection for rotavirus vaccines, with the implications of using serum anti-rotavirus IgA for the assessment of immunogenicity and efficacy in low-income countries unclear.ConclusionsThis study showed no effect of the type of prenatal nutrient supplementation on immune response in this setting. Immune response varied depending on previous exposure to rotavirus, suggesting that alternative delivery modalities and schedules may be considered to improve vaccine performance in high transmission settings.Trial registrationClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT02145000","term_id":"NCT02145000"}}NCT02145000.

Sheila Isanaka and co-workers study nutrient supplementation and infants’ immune responses to rotavirus vaccination.     

An analysis of the cross-reactivity of autoantibodies to GAD65 and GAD67 in diabetes

Background

Autoantibodies to GAD65 (anti-GAD65) are present in the sera of 70–80% of patients with type 1 diabetes (T1D), but antibodies to the structurally similar 67 kDa isoform GAD67 are rare. Antibodies to GAD67 may represent a cross-reactive population of anti-GAD65, but this has not been formally tested.

Methodology/Principal Findings

In this study we examined the frequency, levels and affinity of anti-GAD67 in diabetes sera that contained anti-GAD65, and compared the specificity of GAD65 and GAD67 reactivity. Anti-GAD65 and anti-GAD67 were measured by radioimmunoprecipitation (RIP) using ¹²⁵I labeled recombinant GAD65 and GAD67. For each antibody population, the specificity of the binding was measured by incubation with 100-fold excess of unlabeled GAD in homologous and heterologous inhibition assays, and the affinity of binding with GAD65 and GAD67 was measured in selected sera. Sera were also tested for reactivity to GAD65 and GAD67 by immunoblotting. Of the 85 sera that contained antibodies to GAD65, 28 contained anti–GAD67 measured by RIP. Inhibition with unlabeled GAD65 substantially or completely reduced antibody reactivity with both ¹²⁵I GAD65 and with ¹²⁵I GAD67. In contrast, unlabeled GAD67 reduced autoantibody reactivity with ¹²⁵I GAD67 but not with ¹²⁵I GAD65. Both populations of antibodies were of high affinity (>10¹⁰ l/mol).

Conclusions

Our findings show that autoantibodies to GAD67 represent a minor population of anti-GAD65 that are reactive with a cross-reactive epitope found also on GAD67. Experimental results confirm that GAD65 is the major autoantigen in T1D, and that GAD67 per se has very low immunogenicity. We discuss our findings in light of the known similarities between the structures of the GAD isoforms, in particular the location of a minor cross-reactive epitope that could be induced by epitope spreading.