Crystal structure of a Rad51 filament

Rad51, the major eukaryotic homologous recombinase, is important for the repair of DNA damage and the maintenance of genomic diversity and stability. The active form of this DNA-dependent ATPase is a helical filament within which the search for homology and strand exchange occurs. Here we present the crystal structure of a Saccharomyces cerevisiae Rad51 filament formed by a gain-of-function mutant. This filament has a longer pitch than that seen in crystals of Rad51's prokaryotic homolog RecA, and places the ATPase site directly at a new interface between protomers. Although the filament exhibits approximate six-fold symmetry, alternate protein-protein interfaces are slightly different, implying that the functional unit of Rad51 within the filament may be a dimer. Additionally, we show that mutation of His352, which lies at this new interface, markedly disrupts DNA binding.     

Liquid chromatographic-mass spectrometric determination of endogenous gamma-hydroxybutyrate concentrations in rat brain regions and plasma

A new liquid chromatographic-mass spectrometric (LC-MS) method for determining trace concentrations of gamma-hydroxybutyric acid (GHB) in biological samples has been developed. This method utilizes solid-phase extraction for separation, deuterated GHB as an internal standard (IS) and multiple reaction monitoring (MRM) in the negative ion mode to detect the parent and product ions (103 and 57 for GHB, and 109 and 61 for D6-GHB, respectively). The assay produces excellent linearity and reproducibility, with a limit of quantification (LOQ) of about 0.1 microg/ml. The method has been applied for the determination of endogenous GHB in various rat brain regions.     

Chemical and biological characterization of a polysaccharide biological response modifier from Aloe vera L. var. chinensis (Haw.) Berg

Three purified polysaccharide fractions designated as PAC-I, PAC-II, and PAC-III were prepared from Aloe vera L. var. chinensis (Haw.) Berg. by membrane fractionation and gel filtration HPLC. The polysaccharide fractions had molecular weights of 10,000 kDa, 1300 kDa, and 470 kDa, respectively. The major sugar residue in the polysaccharide fractions is mannose, which was found to be 91.5% in PAC-I, 87.9% in PAC-II, and 53.7% in PAC-III. The protein contents in the polysaccharide fractions was undetectable. NMR study of PAC-I and PAC-II demonstrated the polysaccharides shared the same structure. The main skeletons of PAC-I and PAC-II are beta-(1-->4)-D linked mannose with acetylation at C-6 of manopyranosyl. The polysaccharide fractions stimulated peritoneal macrophages, splenic T and B cell proliferation, and activated these cells to secrete TNF-alpha, IL-1 beta, INF-gamma, IL-2, and IL-6. The polysaccharides were nontoxic and exhibited potent indirect antitumor response in murine model. PAC-I, which had the highest mannose content and molecular weight, was found to be the most potent biological response modifier of the three fractions. Our results suggested that the potency of aloe polysaccharide fraction increases as mannose content and molecular weight of the polysaccharide fraction increase.     

High prevalence of phagocytic-resistant capsular serotypes of Klebsiella pneumoniae in liver abscess

To better understand the role of capsular polysaccharide (CPS) K1 or K2 in Klebsiella pneumoniae liver abscess as well as the development of metastasis to eye, neutrophil phagocytosis of 70 CPS isolates including K1 (n = 23)/K2 (n = 10), non-K1/K2 (n = 37) was evaluated by flow cytometry, fluorescence imaging, and electron microscopy. K1/K2 isolates were significantly more resistant to phagocytosis (P < 0.0001) than non-K1/K2 isolates and displayed increased resistance to intracellular killing. Although mucoid phenotype (M-type) K1/K2 isolates were significantly more resistant to phagocytosis (P = 0.0029) than M-type non-K1/K2, no significant difference in the phagocytosis rate was observed between K1/K2 isolates with M-type and non-M-type (P = 0.0924). Mucoidy is an associated factor that was predominant in K1/K2 isolates, but which itself is not an independent influence on phagocytic resistance. The K1/K2 CPS proved significantly more resistant to phagocytosis than non-K1/K2 CPS in liver abscess isolates (P < 0.0001) and non-abscess isolates (P = 0.0001), suggesting that K1/K2 isolates were generally more virulent in both liver abscess and in non-liver abscess conditions. These findings indicate that resistance of CPS K1 or K2 K. pneumoniae to phagocytosis and intracellular killing presumably contributes to their high prevalence in liver abscess and uniquely in endophthalmitis.     

Translocation of a human focal adhesion LIM-only protein, FHL2, during myofibrillogenesis and identification of LIM2 as the principal determinants of FHL2 focal adhesion localization

LIM domain proteins are found to be important regulators in cell growth, cell fate determination, cell differentiation, and remodeling of the cell cytoskeleton. Human Four-and-a-half LIM-only protein 2 (FHL2) is expressed predominantly in human heart and is only slightly expressed in skeletal muscle. Since FHL2 is an abundant protein in human heart, it may play an important role in the regulation of cell differentiation and myofibrillogenesis of heart at defined subcellular compartment. Therefore, we hypothesized that FHL2 act as a multi-functional protein by the specific arrangement of the LIM domains of FHL2 and that one of the LIM domains of FHL2 can function as an anchor and localizes it into a specific subcellular compartment in a cell type specific manner to regulate myofibrillogenesis. From our results, we observed that FHL2 is localized at the focal adhesions of the C2C12, H9C2 myoblast as well as a nonmyogenic cell line, HepG2 cells. Colocalization of vinculin-CFP and FHL2-GFP at focal adhesions was also observed in cell lines. Site-directed mutagenesis, in turn, suggested that the second LIM domain-LIM2 is essential for its specific localization to focal adhesions. Moreover, FHL2 was observed along with F-actin and focal adhesion of C2C12 and H9C2 myotubes. Finally, we believe that FHL2 moves from focal adhesions and then stays at the Z-discs of terminally differentiated heart muscle.     

Studies of the erythrocyte spectrin tetramerization region

Human erythrocyte spectrin dimers associate at the N-terminal region of alpha spectrin (alpha N) and the C-terminal region of beta-spectrin (beta C) to form tetramers. We have prepared model peptides to study the tetramerization region. Based on phasing information obtained from enzyme digests, we prepared spectrin fragments consisting of the first 156 amino-acid residues and the first 368 amino-acid residues of alpha-spectrin (Sp alpha 1-156 and Sp alpha 1-368, respectively), and found that both peptides associate with a beta-spectrin model peptide, with an affinity similar to that found in alpha beta dimer tetramerization. Spin label EPR studies show that the region consisting of residues 21-46 in alpha-spectrin is helical even in the absence of its beta-partner. Multi-dimensional nuclear magnetic resonance studies of samples with and without a spin label attached to residue 154 show that Sp alpha 1-156 consists of four helices, with the first helix unassociated with the remaining three helices, which bundle to form a triple helical coiled coil bundle. A comparison of the structures of erythrocyte spectrin with other published structures of Drosophila and chicken brain spectrin is discussed. Circular dichroism studies show that the lone helix in Sp alpha-156 associates with helices in the beta peptide to form a coiled coil bundle. Based on NMR and CD results, we suggest that the helices in Sp alpha 1-156 exhibit a looser (frayed) conformation, and that the helices convert to a tighter conformation upon association with its beta-partner. This suggestion does not rule out possible conversion of a non-structured conformation to a structured conformation in various parts of the molecule upon association. Spectrin mutations at residues 28 and 45 of alpha-spectrin have been found in patients with hereditary elliptocytosis. NMR studies were also carried out on Sp alpha 1-156R28S, Sp alpha 1-156R45S and Sp alpha 1-156R45T. A comparison of the structures of Sp alpha 1-156 and Sp alpha 1-156R28S, Sp alpha 1-156R45S and Sp alpha 1-156R45T is discussed.     

Rational design of a potent, long-lasting form of interferon: a 40 kDa branched polyethylene glycol-conjugated interferon alpha-2a for the treatment of hepatitis C

A potent, long-lasting form of interferon alpha-2a mono-pegylated with a 40 kilodalton branched poly(ethylene glycol) was designed, synthesized, and characterized. Mono-pegylated interferon alpha-2a was comprised of four major positional isomers involving Lys31, Lys121, Lys131, and Lys134 of interferon. The in vitro anti-viral activity of pegylated interferon alpha-2a was found to be only 7% of the original activity. In contrast, the in vivo antitumor activity was severalfold enhanced compared to interferon alpha-2a. Pegylated interferon alpha-2a showed no immunogenicity in mice. After subcutaneous injection of pegylated interferon alpha-2a, a 70-fold increase in serum half-life and a 50-fold increase in mean plasma residence time concomitant with sustained serum concentrations were observed relative to interferon alpha-2a. These preclinical results suggest a significantly enhanced human pharmacological profile for pegylated interferon alpha-2a. Results of Phase II/III hepatitis C clinical trials in humans confirmed the superior efficacy of pegylated interferon alpha-2a compared to unmodified interferon alpha-2a.     

High-level expression and purification of immunogenic recombinant SAG1 (P30) of Toxoplasma gondii in Escherichia coli

Surface antigen 1 (SAG1) of Toxoplasma gondii is a good candidate for diagnosis and vaccine development, but recombinant SAG1 produced in Escheichia coli often loses its specific immunogenicity due to the incorrect folding. In the present study, a truncated SAG1 was highly expressed in E. coli as a fusion protein, about 30% of the total protein of the cell lysate. After a simple purification and refolding procedure, purified rSAG1 can be recognized by human Toxoplasma-infective serum, and ELISA kits constructed by rSAG1 can sensitively and specifically detect toxoplasma infection.     

Protein-protein interaction of FHL3 with FHL2 and visualization of their interaction by green fluorescent proteins (GFP) two-fusion fluorescence resonance energy transfer (FRET)

LIM domain proteins are found to be important regulators in cell growth, cell fate determination, cell differentiation and remodeling of the cell cytoskeleton. Human Four-and-a-half LIM-only protein 3 (FHL3) is a type of LIM-only protein that contains four tandemly repeated LIM motifs with an N-terminal single zinc finger (half LIM motif). FHL3 expresses predominantly in human skeletal muscle. In this report, FHL3 was shown to be a novel interacting partner of FHL2 using the yeast two-hybrid assay. Furthermore, site-directed mutagenesis of FHL3 indicated that the LIM2 of FHL3 is the essential LIM domain for interaction with FHL2. Green fluorescent protein (GFP) was used to tag FHL3 in order to study its distribution during myogenesis. Our result shows that FHL3 was localized in the focal adhesions and nucleus of the cells. FHL3 mainly stayed in the focal adhesion during myogenesis. Moreover, using site-directed mutagenesis, the LIM1 of FHL3 was identified as an essential LIM domain for its subcellular localization. Mutants of GFP have given rise to a novel technique, two-fusion fluorescence resonance energy transfer (FRET), in the determination of protein-protein interaction at particular subcellular locations of eukaryotic cells. To determine whether FHL2 and FHL3 can interact with one another and to locate the site of this interaction in a single intact mammalian cell, we fused FHL2 and FHL3 to different mutants of GFP and studied their interactions using FRET. BFP/GFP fusion constructs were cotransfected into muscle myoblast C2C12 to verify the colocalization and subcellular localization of FRET. We found that FHL2 and FHL3 were colocalized in the mitochondria of the C2C12 cells and FRET was observed by using an epi-fluorescent microscope equipped with an FRET specific filter set.