Protein interaction for an interferon-inducible systemic lupus associated gene, IFIT1.

OBJECTIVE: To identify disease-related genes and immune-regulatory pathways in the pathogenesis of systemic lupus erythematosus (SLE) by using gene expression profiling and protein-protein interaction analysis. METHODS: Peripheral white blood cell gene expression profiles of 10 SLE patients were determined by oligonucleotide microarray analysis. Clustering of the gene expression profile was compared with the clinical immune phenotype. SLE-induced genes that were over- or under-expressed were determined and independently validated using a real-time polymerase chain reaction (PCR) method. To study their potential function and the possible pathways involved, a candidate gene was cloned and a GST (glutathione S-transferase) fusion protein was expressed in Escherichia coli. The fusion protein was further purified using the glutathione Sepharose 4B system, and was treated as bait to capture prey from SLE peripheral white blood cell lysate. MALDI-TOF (matrix-assisted laser desorption/ionization-time-of-flight) mass spectrometry was then performed to determine the prey protein. RESULTS: Similarity was found between the gene expression profile and the immune phenotype clusters of the SLE patients. More than 20 disease-associated genes were identified, some of which have not been related to SLE previously. Of these genes, a cluster of interferon-induced genes were highly correlated. IFIT1 (interferon-induced with tetratricopeptide repeats 1) was one of these genes, and overexpression of its mRNA was confirmed independently by real-time PCR in a larger population (40 SLE patients and 29 normal controls). An IFIT1 protein- protein interaction study showed that IFIT1 may interact with Rho/Rac guanine nucleotide exchange factor. CONCLUSION: The gene expression profile seems to be the molecular basis of the diverse immune phenotype of SLE. On the basis of the SLE-related genes found in this study, we suggest that the interferon-related immune pathway is important in the pathogenesis of SLE. IFIT1 is the first gene described as a candidate gene for SLE, and may function by activating Rho proteins through interaction with Rho/Rac guanine nucleotide exchange factor. IFIT1 and the interferon-related pathway may provide potential targets for novel interventions in the treatment of SLE.

Structure of a bulgecin-inhibited g-type lysozyme from the egg white of the Australian black swan. A comparison of the binding of bulgecin to three muramidases.

Bulgecin A, a bacterial metabolite, has been shown to bind in the active-site groove of the chicken-type lysozyme from the rainbow trout (RBTL) and in the lysozyme-like C-terminal domain, of a soluble lytic transglycosylase (C-SLT) from Escherichia coli. These enzymes are muramidases that cleave the glycosidic bonds in the glycan strands of the murein polymer. Here we report the crystal structure of a complex between the goose-type lysozyme from the egg white of the Australian black swan (SEWL) and bulgecin A at 2.45 A resolution. As is the case for the C-SLT/bulgecin and RBTL/bulgecin complexes, the ligand binds with the N-acetylglucosamine ring in subsite C and the proline moiety in site D where it interacts with the catalytic glutamic acid. The taurine residue interacts with the beta-sheet region. Comparisons of the three buigecin complexes show that the inhibitor has the same binding mode to the muramidases with similar protein-ligand interactions, particularly for SEWL and RBTL. From our results, it seems likely that bulgecin, in general, inhibits enzymes with lysozyme-like domains and thus might represent a novel class of natural antibiotics that act on murein-degrading rather than murein-synthesizing enzymes.

Molecular structure and absolute configuration of the diterpene lactone, praelolide.

Praelolide is a new compound which was isolated out from the gorgonian, Menella praelonga (Ridley), collected from the South Sea of China at Zhanjiang, Guangdong. The molecular formula is C28H35O12Cl. The research result by X-ray diffraction method on the crystal structure is presented. The compound is orthorhombic with space group P2(1)2(1)2, cell dimensions a = 16.936, b = 16.709, c = 10.333 A, and Z = 4. The structure has been solved by direct method and refined to R = 0.055 for 2257 unique observable reflexions by least-squares. The molecule is composed of the major conformational isomer in which the three main rings (a six-membered ring, an eight-membered ring, a six-membered ring) take separately the form of chair-chairboat-chair, a five-membered actone ring, a C1 substitution, 4 acetate groups, and a three-membered epoxide ring. The absolute configuration of the molecule has also been determined by statistics (R factor ratio R = 1.012) and Bijvoet pairs observation. For 30 pairs of the greatest anomalous contributions the residuals are R'(+) = 0.057 for the first enantiomorph and R'(-) = 0.005 for the second one, so the latter should unambiguously correspond to the absolute configuration of the molecule.