Halilectin 1 (H‐1) and Halilectin 2 (H‐2): two new lectins isolated from the marine sponge Haliclona caerulea

Two new lectins named Halilectin 1 (H‐1) and Halilectin 2 (H‐2) were isolated from the marine sponge Haliclona caerulea using a combination of affinity chromatography on stroma fixed onto Sephadex G‐25 and cation and anion exchange chromatography. H‐1 is a monomeric protein with a molecular mass of 40 kDa estimated using sodium dodecyl sulfate polyacrylamide gel electrophoresis and 15 kDa estimated using a TSK gel. Conversely, H‐2 is a homodimeric protein with 15 kDa monomers linked via weak interactions. H‐1 more effectively agglutinates trypsinized rabbit erythrocytes, whereas H‐2 more effectively agglutinates native rabbit erythrocytes. The hemagglutinating activity of H‐1 could be not inhibited by any tested sugars, but H‐2 was inhibited by orosomucoid and porcine stomach mucin. Neither lectin was dependent on divalent ions. H‐1 was stable at basic pH range and temperatures up to 50 °C, whereas H‐2 was stable at acid pH range and temperatures up to 80 °C. The H. caerulea lectins exhibited dose‐dependent toxicity against Artemia nauplii. Additionally, 76% of the primary structure of H‐2 was determined using tandem mass spectrometry to contain a unique amino acid sequence with no similarity to any members of the animal lectin family. Copyright © 2012 John Wiley & Sons, Ltd.     

Purification and primary structure of a mannose/glucose‐binding lectin from Parkia biglobosa Jacq. seeds with antinociceptive and anti‐inflammatory properties

Parkia biglobosa (subfamily Mimosoideae), a typical tree from African savannas, possess a seed lectin that was purified by combination of ammonium sulfate precipitation and affinity chromatography on a Sephadex G‐100 column. The P. biglobosa lectin (PBL) strongly agglutinated rabbit erythrocytes, an effect that was inhibited by d ‐mannose and d ‐glucose‐derived sugars, especially α‐methyl‐d ‐mannopyranoside and N‐acetyl‐d ‐glucosamine. The hemagglutinating activity of PBL was maintained after incubation at a wide range of temperature and pH and also was independent of divalent cations. By sodium dodecyl sulfate–polyacrylamide gel electrophoresis analysis, PBL exhibited an electrophoretic profile consisting of a single band with apparent molecular mass of 45 kDa. An analysis using electrospray ionization–mass spectrometry indicated that purified lectin possesses a molecular average mass of 47 562 ± 4 Da, and the analysis by gel filtration showed that PBL is a dimer in solution. The complete amino acid sequence of PBL, as determined using tandem mass spectrometry, consists of 443 amino acid residues. PBL is composed of a single non‐glycosylated polypeptide chain of three tandemly arranged jacalin‐related domains. Sequence heterogeneity was found in six positions, indicating that the PBL preparations contain highly homologous isolectins. PBL showed important antinociceptive activity associated to the inhibition of inflammatory process. Copyright © 2013 John Wiley & Sons, Ltd.     

Electroencephalographic Characterization of Pentylenetetrazole Kindling in Rats and Modulation of Epileptiform Discharges by Nitric Oxide

Epileptogenesis is a progressive process which culminates with spontaneous, recurrent and unpredictable epileptic seizures due to enhanced neuronal excitability. Well-characterized animal models of this process are needed to clarify its underlying molecular mechanisms, in which the role of nitric oxide has been a controversial component. We have used kindling with a sub-convulsive dose of pentylenetetrazole to objectively characterize early electroencephalographic changes during epileptogenesis. We used electroencephalographic recordings both during pentylenetetrazole (20 mg/kg) kindling for 20 days and then, 24 days later to quantify the number, duration and spectral power of epileptic discharges. The levels of nitric oxide were modulated locally in the cerebral cortex by pharmacological agents. The number of epileptiform discharges increased during the kindling protocol as well as 24 days later, revealing the induction of a self-sustaining epileptogenic process. Epileptic discharges were characterized by theta frequencies (4–10 Hz) that were associated with absence-like seizures. However, during kindling, the spectral power of the theta band progressively decreased, while the power of higher frequencies, in the beta band, increased. Nitric oxide in the cerebral cortex inhibited the number and amplitude of epileptic discharges. The electroencephalographic characterization of this kindling protocol provides a valuable tool to detect consequences of therapeutic interventions undertaken at initial phases of epileptogenesis, especially those targeted towards stopping this process. Increases of nitric oxide in the cerebral cortex could be a useful intervention to negatively modulate neuronal excitability, epileptic discharges and the progression of epileptogenesis.     

Systematic reinstatement of Schilbe depressirostris (Peters, 1852), based on differences in DNA barcoding and morphology,from Schilbe intermedius Rüppell, 1832 (Siluriformes,Schilbeidae)

Climate change poses an unprecedented threat to biodiversity worldwide. Consequently, unrecognised taxa may not receive adequate conservation attention to survive. We used molecular and morphological data to address the challenge of species delimitation within the genus Schilbe. The presence or absence of an adipose fin and distribution based on east-flowing, conceivably faster-flowing, or west-flowing, probably more slow-flowing, river systems were considered. Distinctive geographic patterns in genetic variation within southern, eastern, and western African populations were revealed. Particularly, the South African population is distinct from those of Namibia, Botswana and Nigeria. No individuals with rudimentary adipose fins were found at any locality, but specimens from three localities either had or did not have adipose fins. These mixed occurrences are suspected to be a result of human interventions, and that the presence of rudimentary adipose fins in the east African species could be an adaptive feature that serves to stabilise these fish in faster currents. In addition, the genetic divergence observed among African silver catfish from geographically isolated river systems is conceivably the result of micro-evolutionary adaptive responses to different environmental conditions. Collectively, these results distinguish S. depressirostris from S. intermedius.     

Functional and structural insight into properdin control of complement alternative pathway amplification

Properdin (FP) is an essential positive regulator of the complement alternative pathway (AP) providing stabilization of the C3 and C5 convertases, but its oligomeric nature challenges structural analysis. We describe here a novel FP deficiency (E244K) caused by a single point mutation which results in a very low level of AP activity. Recombinant FP E244K is monomeric, fails to support bacteriolysis, and binds weakly to C3 products. We compare this to a monomeric unit excised from oligomeric FP, which is also dysfunctional in bacteriolysis but binds the AP proconvertase, C3 convertase, C3 products and partially stabilizes the convertase. The crystal structure of such a FP-convertase complex suggests that the major contact between FP and the AP convertase is mediated by a single FP thrombospondin repeat and a small region in C3b. Small angle X-ray scattering indicates that FP E244K is trapped in a compact conformation preventing its oligomerization. Our studies demonstrate an essential role of FP oligomerization in vivo while our monomers enable detailed structural insight paving the way for novel modulators of complement.