A novel thermophilic endo-β-1,4-mannanase from Aspergillus nidulans XZ3: functional roles of carbohydrate-binding module and Thr/Ser-rich linker region

The gene man5XZ3 from Aspergillus nidulans XZ3 encodes a multimodular β-mannanase of glycoside hydrolase family 5 that consists of a family 1 carbohydrate-binding module (CBM1), a Thr/Ser-rich linker region, and a catalytic domain. Recombinant Man5XZ3 and its two truncated derivatives, Man5ΔCBM (removing the CBM1) and Man5ΔCL (removing both the CBM1 and linker region), were produced in Pichia pastoris and showed significant variance in the secondary structure. The three enzymes had similar biochemical properties, such as optimal pH and temperature (pH 5.0 and 80 °C) and excellent pH stability at pH 4.0–10.0. Removal of the CBM1 alone could improve the thermostability of Man5XZ3, but further removal of the linker region resulted in worse thermostability. Man5XZ3 retained greater enzyme activity in the presence of an organic solvent (acetone), two detergents (SDS and Triton X-100), and a chaotropic agent (urea) compared with Man5ΔCBM and Man5ΔCL. This study provides an excellent β-mannanase candidate favorable for various industries and primarily demonstrates the relationship between enzyme structure and function.     

<Emphasis Type="Italic">fabC</Emphasis> of <Emphasis Type="Italic">Streptomyces lydicus</Emphasis> involvement in the biosynthesis of streptolydigin

Streptolydigin, a secondary metabolite produced by Streptomyces lydicus, is a potent inhibitor of bacterial RNA polymerases. It has been suggested that streptolydigin biosynthesis is associated with polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS). Thus, there is great interest in understanding the role of fatty acid biosynthesis in the biosynthesis of streptolydigin. In this paper, we cloned a type II fatty acid synthase (FAS II) gene cluster of fabDHCF from the genome of S. lydicus and constructed the SlyfabCF-disrupted mutant. Sequence analysis showed that SlyfabDHCF is 3.7 kb in length and encodes four separated proteins with conserved motifs and active residues, as shown in the FAS II of other bacteria. The SlyfabCF disruption inhibited streptolydigin biosynthesis and retarded mycelial growth, which were likely caused by the inhibition of fatty acid synthesis. Streptolydigin was not detected in the culture of the mutant strain by liquid chromatography–mass spectrometry. Meanwhile, the streptolol moiety of streptolydigin accumulated in cultures. As encoded by fabCF, acyl carrier protein (ACP) and β-ketoacyl-ACP synthase II are required for streptolydigin biosynthesis and likely involved in the step between PKS and NRPS. Our results provide the first genetic and metabolic evidence that SlyfabCF is shared by fatty acid synthesis and antibiotic streptolydigin synthesis.     

Comparison of the three-dimensional structure of two human rhinoviruses (HRV2 and HRV14)

An attempt has been made to build a model of human rhinovirus 2 (HRV2) based on the known human rhinovirus 14 (HRV14) structure. HRV2 was selected because its amino acid sequence is known and because it belongs to the minor rhinovirus receptor class as compared to HRV14, which belongs to the major class. Initial alignment of HRV2 with HRV14 based on the primary sequence and the knowledge of the three-dimensional structure of HRV14 showed that the most probable position of the majority of insertions and deletions occurred in the vicinity of the neutralizing immunogenic sites (NIm). Out of a total of 855 amino acids present in one copy of each of the capsid proteins VP1 through VP4 of HRV14, 411 are different between the two viruses. There are also 6 amino acid residues inserted and 14 residues deleted in HRV2 relative to HRV14. Examination of amino acid interactions showed several cases of conservation of function, e.g., salt bridges or the filling of restricted space. The largest variation amongst the residues lining the canyon, the putative receptor binding site, was in the carboxy-terminal residues of VP1.     

Inositol pyrophosphates are required for DNA hyperrecombination in protein kinase c1 mutant yeast

Diphosphoinositol pentakisphosphate (InsP(7)) and bis-diphosphoinositol tetrakisphosphate (InsP(8)) contain energetic pyrophosphate groups, occur throughout animal and plant kingdoms, and are synthesized by a recently cloned family of inositol hexakisphosphate kinases (InsP(6)Ks). We report that these inositol pyrophosphates mediate homologous DNA recombination in yeast S. cerevisae. Hyperrecombination, caused by altered protein kinase C1 (PKC1), is lost in yeast with deletion of yeast InsP(6)K (yInsP(6)K) and can be restored selectively by catalytically active yeast or mammalian InsP(6)Ks. Inositol pyrophosphates are required for two forms of hyperrecombination that differ in mechanism, suggesting some generalities for actions of inositol pyrophosphates in recombination.     

Exploring the stereochemistry of CXCR4-peptide recognition and inhibiting HIV-1 entry with D-peptides derived from chemokines

Chemokine receptor CXCR4 plays an important role in the immune system and the cellular entry of human immunodeficiency virus type 1 (HIV-1). To probe the stereospecificity of the CXCR4-ligand interface, d-amino acid peptides derived from natural chemokines, viral macrophage inflammatory protein II (vMIP-II) and stromal cell-derived factor-1alpha (SDF-1alpha), were synthesized and found to compete with (125)I-SDF-1alpha and monoclonal antibody 12G5 binding to CXCR4 with potency and selectivity comparable with or higher than their l-peptide counterparts. This was surprising because of the profoundly different side chain topologies between d- and l-enantiomers, which circular dichroism spectroscopy showed adopt mirror image conformations. Further direct binding experiments using d-peptide labeled with fluorescein (designated as FAM-DV1) demonstrated that d- and l-peptides shared similar or at least overlapping binding site(s) on the CXCR4 receptor. Structure-activity analyses of related peptide analogs of mixed chiralities or containing alanine replacements revealed specific residues at the N-terminal half of the peptides as key binding determinants. Acting as CXCR4 antagonists and with much higher biological stability than l-counterparts, the d-peptides showed significant activity in inhibiting the replication of CXCR4-dependent HIV-1 strains. These results show the remarkable stereochemical flexibility of the CXCR4-peptide interface. Further studies to understand the mechanism of this unusual feature of the CXCR4 binding surface might aid the development of novel CXCR4-binding molecules like the d-peptides that have high affinity and stability.     

Intrathecal Fas ligand infusion strengthens immunoprivilege of central nervous system and suppresses experimental autoimmune encephalomyelitis

Fas ligand (FasL) is an essential molecule strongly expressed in some immunoprivileged sites, but is expressed at very low levels in normal CNS. In this study, acute experimental autoimmune encephalomyelitis (EAE) was induced in Lewis rats with guinea pig myelin basic protein. Intrathecal infusion of recombinant FasL before EAE onset dose dependently suppressed acute EAE and alleviated pathological inflammation in lumbosacral spinal cord. This treatment greatly increased apoptosis in CNS inflammatory cells, but did not inhibit systemic immune response to myelin basic protein. Systemic administration of a similar dose of rFasL was ineffective. In vitro, encephalitogenic T cells were highly sensitive to rFasL-induced cell death, and activated macrophages were also susceptible. In addition, in vitro rFasL treatment potentiated the immunosuppressive property of rat cerebrospinal fluid. We conclude that intrathecal infusion of rFasL eliminated the initial wave of infiltrating T cells and macrophages, and therefore blocked the later recruitment of inflammatory cells into CNS. Although Fas receptor expression was observed on spinal cord neurons, astrocytes, and oligodendrocytes, no damage to these cells or to the myelin structure was detected after rFasL infusion.     

Sequence, distribution and quantification of the motilin precursor in the cat

Due to motilin's relation to the migrating motor complex (MMC), the physiology of motilin has been mostly studied in man and dog. The cat does not have an MMC pattern, and little is known about cat motilin. Therefore we identified the cat motilin precursor (GenBank accession no. AF127917) and developed a quantitative polymerase chain reaction (PCR) to explore its distribution in the gastrointestinal tract and in the central nervous system (CNS). The precursor is closely related to the dog precursor and consists of an open reading frame of 348bp encoding the signal peptide (25 amino acids), the motilin sequence (22 amino acids) and the motilin associated peptide (69 amino acids). One amino acid of the signal peptide was subject to gene polymorphism. Quantification of motilin messenger RNA (mRNA) was for the first time achieved. It is most abundant in the gastrointestinal tract, with the highest concentration in the duodenum, the lowest in the colon and is not detectable in the corpus. However an important expression was also observed in several regions of the CNS, except the striatum and cerebral cortex. The highest level was in the hypothalamus (although 23-fold lower than in the duodenum), the lowest level in the pons. Moderate levels were found in the thyroid. These data suggest that the physiological role of motilin may extend beyond its effect on gastrointestinal motility.     

Targeting CDH17 Suppresses Tumor Progression in Gastric Cancer by Downregulating Wnt/β-Catenin Signaling

Purpose

Gastric cancer remains one of the leading causes of cancer death worldwide. Patients usually present late with local invasion or metastasis, for which there are no effective therapies available. Following previous studies that identified the adhesion molecule Cadherin-17(CDH17) as a potential marker for gastric carcinoma, we performed proof-of-principle studies to develop rational therapeutic approaches targeting CDH17 for treating this disease.

Methods

Immunohistochemistry was used to study the expression of CDH17 in 156 gastric carcinomas, and the relationship between survival and CDH17 expression was studied by multivariate analyses. The effect of RNA interference–mediated knockdown of CDH17 on proliferation of gastric carcinoma cell lines was examined in vitro and in vivo, as well as the effects on downstream signaling by immunoblotting.

Results

CDH17 was consistently up-regulated in human gastric cancers, and overall survival in patients with CDH17 upregulation was poorer than in those without expression of this gene (5 yrs overall survival rate 29.0% vs. 45.0%, P<0.01). Functional assays demonstrated that CDH17 knockdown inhibited cell proliferation, adhesion, migration, invasion, clonogenicity and induce G0/G1 arrest. In mice, shRNA-mediated CDH17 knockdown markedly inhibits tumor growth; intratumoral injection of CDH17 shRNAs results in significant antitumor effects on transplanted tumor models. The antitumor mechanisms underlying CDH17 inhibition involve inactivation of Wnt/β-catenin signaling.

Conclusion

Our results identify CDH17 as a biomarker of gastric carcinoma and attractive therapeutic target for this aggressive malignancy.     

Dichloroacetate induces protective autophagy in LoVo cells: involvement of cathepsin D/thioredoxin-like protein 1 and Akt-mTOR-mediated signaling

Dichloroacetate (DCA) is an inhibitor of pyruvate dehydrogenase kinase (PDK), and recently it has been shown as a promising nontoxic antineoplastic agent. In this study, we demonstrated that DCA could induce autophagy in LoVo cells, which were confirmed by the formation of autophagosomes, appearance of punctate patterns of LC3 immunoreactivity and activation of autophagy associated proteins. Moreover, autophagy inhibition by 3-methyladenine (3-MA) or Atg7 siRNA treatment can significantly enhance DCA-induced apoptosis. To determine the underlying mechanism of DCA-induced autophagy, target identification using drug affinity responsive target stability (DARTS) coupled with ESI-Q-TOF MS/MS analysis were utilized to profile differentially expressed proteins between control and DCA-treated LoVo cells. As a result, Cathepsin D (CTSD) and thioredoxin-like protein 1 (TXNL1) were identified with significant alterations compared with control. Further study indicated that DCA treatment significantly promoted abnormal reactive oxygen species (ROS) production. On the other hand, DCA-triggered autophagy could be attenuated by N-acetyl cysteine (NAC), a ROS inhibitor. Finally, we demonstrated that the Akt-mTOR signaling pathway, a major negative regulator of autophagy, was suppressed by DCA treatment. To our knowledge, it was the first study to show that DCA induced protective autophagy in LoVo cells, and the potential mechanisms were involved in ROS imbalance and Akt-mTOR signaling pathway suppression.     

Relative bioavailabilities of organic zinc sources with different chelation strengths for broilers fed diets with low or high phytate content

A six-day experiment was conducted to estimate the relative bioavailability values (RBV) of zinc (Zn) in three organic sources (oZn) with different chelation strengths compared to inorganic ZnSO₄ (iZn) for broilers fed a low or high phytate diet. A total of 1080, one-d-old male broiler chicks were randomly assigned to one of 18 dietary treatments (six replicates cages of ten chicks per cage) in a completely randomized design involving a 2 × 2 × 4 factorial arrangement with two levels of added phytate (0 or 10 g phytate as sodium phytate/kg), two levels of added Zn (30 or 60 mg/kg) and four Zn sources (iZn and three oZn sources) plus one low and one high phytate control treatments without Zn addition. The three oZn sources consisted of (1) Zn amino acid with weak chelation strength (ZnAA-L, formation quotient Q_f = 6.6, containing 119 g Zn/kg), (2) Zn proteinate with moderate chelation strength (ZnPRO-M, Q_f = 30.7, containing 133 g Zn/kg) or (3) Zn proteinate with strong chelation strength (ZnPRO-H, Q_f = 944.0, containing 186 g Zn/kg). Chicks were harvested at 6 days of age and pancreas metallothionein (MT) mRNA expression was used to estimate Zn RBV. Pancreas MT mRNA expression increased (P<0.01) as dietary Zn level increased. Chicks fed high phytate diets had lower (P<0.05) MT mRNA expression than chicks fed low phytate diets. Based on multiple linear regression slope ratios with ZnSO₄ set at 1.00, the RBV of ZnAA-L, ZnPRO-M and ZnPRO-H were 1.01, 1.28 and 0.70, respectively, for low phytate diets, and 1.05, 1.39 and 0.92, respectively, for high phytate diets. The slope for the oZn source with moderate chelation strength differed (P<0.05) from iZn and the other two oZn sources. The RBV of ZnAA-L, ZnPRO-M and ZnPRO-H under the high phytate diet increased by 0.04, 0.11 and 0.22, respectively, compared to those under the low phytate diet. Results indicate that the oZn sources with moderate or strong chelation strength offer partial or complete resistance to interference from high dietary phytate during digestion; and the oZn with moderate chelation strength had a greater RBV with both low and high phytate diets than iZn or oZn sources with weak or strong chelation strength.