Structure of Pyridoxal Kinase from Sheep Brain and Role of the Tryptophanyl Residues

The primary structure of sheep brain pyridoxal kinase has been determined by direct chemical and physical methods. The enzyme contains 312 amino acid residues with an acetylated methionine at the N-terminus, yielding a molecular mass of 34,861 Da. The functional role played by the two tryptophanyl residues in positions 52 and 244 of the polypeptide chain has been investigated by fluorescence spectroscopy. The tryptophanyl residues are not completely exposed to the rapidly relaxing solvent and they are poorly accessible to collisional quenchers. Chemical modification with NBS abolishes the catalytic activity of the kinase. The amino acid sequence of the sheep brain enzyme shows high similarity (86.2% identity) with the human pyridoxal kinase recently reported [Hanna, Turner, and Kirkness, (1997), J. Biol. Chem. 272, 10756–10760]. Comparison of the mammalian proteins with bacterial and yeast putative pyridoxal kinases retrieved from the Swiss-Prot data bank shows a low degree of overall similarity. In particular, the putative ATP-binding domain is conserved, whereas the region that appears to be crucial in the binding of the pyridoxal substrate is not. Thus, the assignment of the bacterial and yeast cDNA-deduced proteins as pyridoxal kinases should be taken with caution.     

Heterologous expression of bovine and porcine beta-lactoglobulins in Pichia pastoris: towards a comparative functional characterisation

Bovine and porcine beta-lactoglobulins were cloned and expressed in host cells with the aim of developing the tools necessary for their structural, functional and conformational characterisation by NMR techniques. Both lipocalins were expressed in Pichia pastoris, where the use of a constitutive promoter turned out to allow the highest productivity. The yield of recombinant proteins was further improved through multiple integration of the encoding genes and by increasing aeration of the transformed cultures. Both proteins were obtained in the culture medium at the concentration of 200 microg/ml. Recombinant lipocalins were purified by ion-exchange chromatography from the culture medium. A preliminary NMR characterisation showed that both proteins were correctly folded.     

Synthesis, radiolabeling, and preliminary biological evaluation of [3H]-1-[(S)-N,O-bis-(isoquinolinesulfonyl)-N-methyl-tyrosyl]-4-(o-tolyl)-piperazine, a potent antagonist radioligand for the P2X7 receptor

The design, synthesis, and preliminary biological evaluation of the first potent radioligand antagonist for the P2X(7) receptor, named [(3)H]-1-[(S)-N,O-bis-(isoquinolinesulfonyl)-N-methyl-tyrosyl]-4-(o-tolyl)-piperazine (compound 13), are reported. This compound bound to human P2X(7) receptors expressed in HEK transfected cells with K(D) and B(max) value of 3.46+/-0.1 nM and 727+/-73 fmol/mg of protein, respectively. The high affinity and facile labeling makes it a promising radioligand for a further characterization of P2X(7) receptor subtype.     

Marked inhibition of retinal neovascularization in rats following soluble-flt-1 gene transfer

BACKGROUND: In mouse models of retinopathy of prematurity (ROP) inhibitors of vascular endothelial growth factor (VEGF) functions administered systemically completely block retinal neovascularization. In contrast, selective ocular VEGF depletion has achieved an approx. 50% inhibition of retinal neovascular growth. It is unclear whether a more complete inhibition of new blood vessel development can be obtained with an anti-VEGF therapy localized to the eye. Therefore, the objective of the present study was to determine the effect of local anti-VEGF therapy in a different animal model which closely mimics human ROP. METHODS: Rats were exposed to alternating cycles of high and low levels of oxygen for 14 days immediately after birth; thereafter, they were intravitreally injected with an adenoviral vector expressing a secreted form of the VEGF receptor flt-1 (Ad.sflt), which acts by sequestering VEGF. Contralateral eyes were injected with the control vector carrying the reporter gene expressing beta-galactosidase (Ad.betaGal). RESULTS: At the peak of retinal neovascular growth, i.e. post-natal day 21 (P21), we observed up to 97.5% decrease in retinal neovascularization in animals injected with Ad.sflt. At the end of observation (P28), no significant difference in retinal vessel number was detected in both oxygen-injured and normoxic Ad.sflt-treated retinas compared with untreated or Ad.betaGal-treated retinas. CONCLUSION: Adenoviral-mediated sflt-1 gene transfer induces a near-complete inhibition of ischemia-induced retinal neovascularization in rats without affecting pre-existing retinal vessels.     

Therapeutic potential of yeast killer toxin-like antibodies and mimotopes

This review focuses on the potential of yeast killer toxin (KT)-like antibodies (KTAbs), that mimic a wide-spectrum KT through interaction with specific cell wall receptors (KTR) and their molecular derivatives (killer mimotopes), as putative new tools for transdisease anti-infective therapy. KTAbs are produced during the course of experimental and natural infections caused by KTR-bearing micro-organisms. They have been produced by idiotypic vaccination with a KT-neutralizing mAb, also in their monoclonal and recombinant formats. KTAbs and KTAbs-derived mimotopes may exert a strong therapeutic activity against mucosal and systemic infections caused by eukaryotic and prokaryotic pathogenic agents, thus representing new potential wide-spectrum antibiotics.     

In vitro effect of indomethacin and interferon-alpha on Th1 and Th2 cytokine synthesis in patients with chronic hepatitis C

Current evidences suggest that non-steroidal anti-inflammatory drugs could enhance the antiviral activity of interferon-alpha in chronic HCV infection. In this study, we investigated the effect of indomethacin, a non-steroidal anti-inflammatory drug, and interferon-alpha on cytokine production by peripheral blood mononuclear cells from 12 untreated patients with chronic hepatitis C. We evaluated the effect of incubation with indomethacin, interferon-alpha or both on synthesis of Th1- (interleukin-2, interferon-gamma) and Th2-associated cytokines (interleukin-4, interleukin-10), and of the antiviral protein 2',5'-oligoadenylate synthetase. Interferon-alpha induced a significant increase in production of interleukin-2. Smaller increases were also seen in the presence of indomethacin, while incubation with both indomethacin and interferon-alpha leads to a synergistic effect. Incubation with indomethacin decreased both interleukin-4 and interleukin-10, whereas interferon-alpha increased these cytokines. The addition of indomethacin to interferon-alpha significantly reversed this interferon-induced increase. Finally, both indomethacin and the association interferon-alpha plus indomethacin determined a significant increase in 2',5'-oligoadenylate synthetase production compared to both baseline and interferon-alpha alone. In conclusion, indomethacin was able to enhance the antiviral activity of interferon-alpha and to modulate the interferon-induced Th1 and Th2 cytokine response by increasing the Th1-response, fundamental for sustained clearance of HCV, and by decreasing the Th-2 type response, associated with HCV persistence.     

Glutamate 59 is critical for transport function of the amino acid cotransporter KAAT1

KAAT1 is a neutral amino acid transporter activated by K⁺ or by Na⁺ (9). The protein shows significant homology with members of the Na⁺/Cl^–-dependent neurotransmitter transporter super family. E59G KAAT1, expressed in Xenopus oocytes, exhibited a reduced leucine uptake [20–30% of wild-type (WT)], and kinetic analysis indicated that the loss of activity was due to reduction of V_max and apparent affinity for substrates. Electrophysiological analysis revealed that E59G KAAT1 has presteady-state and uncoupled currents larger than WT but no leucine-induced currents. Site-directed mutagenesis analysis showed the requirement of a negative charge in position 59 of KAAT1. The analysis of permeant and impermeant methanethiosulfonate reagent effects confirmed the intracellular localization of glutamate 59. Because the 2-aminoethyl methanethiosulfonate hydrobromid inhibition was not prevented by the presence of Na⁺ or leucine, we concluded that E59 is not directly involved in the binding of substrates. N-ethylmaleimide inhibition was qualitatively and quantitatively different in the two transporters, WT and E59G KAAT1, having the same cysteine residues. This indicates an altered accessibility of native cysteine residues due to a modified spatial organization of E59G KAAT1. The arginine modifier phenylglyoxal effect supports this hypothesis: not only cysteine but also arginine residues become more accessible to the modifying reagents in the mutant E59G. In conclusion, the results presented indicate that glutamate 59 plays a critical role in the three-dimensional organization of KAAT1. amino acid transport; structure/function; amino acid modifiers; Manduca sexta     

Celiac disease association with CD8+ T cell responses: identification of a novel gliadin-derived HLA-A2-restricted epitope

One of the diagnostic hallmarks of the histological lesions associated with celiac disease is the extensive infiltration of the small intestinal epithelium by CD8(+) T cells of unknown Ag specificity. In this study, we report recognition of the gliadin-derived peptide (A-gliadin 123-132) by CD8(+) T lymphocytes from celiac patients. A-gliadin 123-132-specific IFN-gamma production and cytotoxic activity were detected in PBMCs derived from patients on gluten-free diet, but not from either celiac patients on gluten-containing diet or healthy controls. In contrast, A-gliadin 123-132-specific cells were isolated from small intestine biopsies of patients on either gluten-free or gluten-containing diets. Short-term T cell lines derived from the small intestinal mucosa and specific for the 123-132 epitope recognized human APC pulsed with either whole recombinant alpha-gliadin or a partial pepsin-trypsin gliadin digest. Finally, we speculate on a possible mechanism leading to processing and presentation of class I-restricted gliadin-derived epitopes in celiac disease patients.     

Deletions of any single residues in Glu40-Ser48 loop connecting a domain and the first transmembrane helix of sarcoplasmic reticulum Ca(2+)-ATPase result in almost complete inhibition of conformational transition and hydrolysis of phosphoenzyme intermediate

Possible roles of the Glu40-Ser48 loop connecting A domain and the first transmembrane helix (M1) in sarcoplasmic reticulum Ca(2+)-ATPase (SERCA1a) were explored by mutagenesis. Deletions of any single residues in this loop caused almost complete loss of Ca(2+)-ATPase activity, while their substitutions had no or only slight effects. Single deletions or substitutions in the adjacent N- and C-terminal regions of the loop (His32-Asn39 and Leu49-Ile54) had no or only slight effects except two specific substitutions of Asn39 found in SERCA2b in Darier's disease pedigrees. All the single deletion mutants for the Glu40-Ser48 loop and the specific Asn39 mutants formed phosphoenzyme intermediate (EP) from ATP, but their isomeric transition from ADP-sensitive EP (E1P) to ADP-insensitive EP (E2P) was almost completely or strongly inhibited. Hydrolysis of E2P formed from Pi was also dramatically slowed in these deletion mutants. On the other hand, the rates of the Ca(2+)-induced enzyme activation and subsequent E1P formation from ATP were not altered by the deletions and substitutions. The results indicate that the Glu40-Ser48 loop, with its appropriate length (but not with specific residues) and with its appropriate junction to A domain, is a critical element for the E1P to E2P transition and formation of the proper structure of E2P, therefore, most likely for the large rotational movement of A domain and resulting in its association with P and N domains. Results further suggest that the loop functions to coordinate this movement of A domain and the unique motion of M1 during the E1P to E2P transition.