Specific inhibition and stabilization of aspergilloglutamic peptidase by the propeptide. Identification of critical sequences and residues in the propeptide

Aspergilloglutamic peptidase (formerly called aspergillopepsin II) is an acid endopeptidase produced by Aspergillus niger var. macrosporus, with a novel catalytic dyad of a glutamic acid and a glutamine residue, thus belonging to a novel peptidase family G1. The mature enzyme is generated from its precursor by removal of the putative 41-residue propeptide and an 11-residue intervening peptide through autocatalytic activation. In the present study, the propeptide (Ala1-Asn41) and a series of its truncated peptides were chemically synthesized, and their effects on the enzyme activity and thermal stability were examined to identify the sequences and residues in the propeptide most critical to the inhibition and thermal stabilization. The synthetic propeptide was shown to be a potent competitive inhibitor of the enzyme (Ki = 27 nM at pH 4.0). Various shorter propeptide fragments derived from the central region of the propeptide had significant inhibitory effect, whereas their Ala scan-substituted peptides, especially R19A and H20A, showed only weak inhibition. Substitution of the Pro23-Pro24 sequence near His20 with an Ala-Ala sequence changed the peptide Lys18-Tyr25 to a substrate with His20 as the P1 residue. Furthermore, the propeptide was shown to be able to significantly protect the enzyme from thermal denaturation (DeltaTm = approximately 19 degrees C at pH 5.6). The protective potencies of the propeptide as well as truncated propeptides and their Ala scan-substituted peptides are parallel with their inhibitory potencies. These results indicate that the central part, and especially Arg19 and His20 therein, of the propeptide is most critical to the inhibition and thermal stabilization and that His20 interacts with the enzyme at or near the S1 site in a nonproductive fashion.     

Gene trap mutagenesis-based forward genetic approach reveals that the tumor suppressor OVCA1 is a component of the biosynthetic pathway of diphthamide on elongation factor 2

OVCA1 is a tumor suppressor identified by positional cloning from chromosome 17p13.3, a hot spot for chromosomal aberration in breast and ovarian cancers. It has been shown that expression of OVCA1 is reduced in some tumors and that it regulates cell proliferation, embryonic development, and tumorigenesis. However, the biochemical function of OVCA1 has remained unknown. Recently, we isolated a novel mutant resistant to diphtheria toxin and Pseudomonas exotoxin A from the gene trap insertional mutants library of Chinese hamster ovary cells. In this mutant, the Ovca1 gene was disrupted by gene trap mutagenesis, and this disruption well correlated with the toxin-resistant phenotype. We demonstrated direct evidence that the tumor suppressor OVCA1 is a component of the biosynthetic pathway of diphthamide on elongation factor 2, the target of bacterial ADP-ribosylating toxins. A functional genetic approach utilizing the random gene trap mutants library of mammalian cells should become a useful strategy to identify the genes responsible for specific phenotypes.     

Structural basis for the specificity and catalysis of human Atg4B responsible for mammalian autophagy

Reversible modification of Atg8 with phosphatidylethanolamine is crucial for autophagy, the bulk degradation system conserved in eukaryotic cells. Atg4 is a novel cysteine protease that processes and deconjugates Atg8. Herein, we report the crystal structure of human Atg4B (HsAtg4B) at 1.9-A resolution. Despite no obvious sequence homology with known proteases, the structure of HsAtg4B shows a classical papain-like fold. In addition to the papain fold region, HsAtg4B has a small alpha/beta-fold domain. This domain is thought to be the binding site for Atg8 homologs. The active site cleft of HsAtg4B is masked by a loop (residues 259-262), implying a conformational change upon substrate binding. The structure and in vitro mutational analyses provide the basis for the specificity and catalysis of HsAtg4B. This will enable the design of Atg4-specific inhibitors that block autophagy.     

Application of ultra-high magnetic field for saccharide molecules: 1H NMR spectra of 6-O-alpha-D-glucopyranosyl-cyclomaltoheptaose and -cyclomaltohexaose

1H NMR spectra of G1-alpha-CD and G1-beta-CD were recorded using a spectrometer equipped with a 21.6 T magnet. An ultra-high magnetic field was effective for detecting 1H NMR signals with a small difference in chemical shifts. Introducing a glucosyl group onto CDs as a branch caused deformation of equilibrated 1H signals of cyclodextrin. Particularly, 1H signals in branched glucose were shifted greatly.     

Polymorphism of monolayer lipid membrane structures made from unsymmetrical bolaamphiphiles

The crystal structures of synthetic unsymmetrical 1-glucosamide- and 1-galactosamide bolaamphiphiles, 13-[(beta-d-glucopyranosyl)carbamoyl]tridecanoic acid (1) and 15-[(beta-d-galactopyranosyl)carbamoyl]pentadecanoic acid (2), respectively, were elucidated by single-crystal X-ray analysis. The space group for 1 is P2(1), Z=2 with cell dimensions: a=8.6816(9), b=4.8578(5), c=26.250(3)A, beta=91.460(2) degrees ; that for 2P2(1), Z=2 with cell dimensions: a=4.90(1), b=40.139(1), 6.289(1)A, beta=106.48(1) degrees . The glucopyranosyl and galactopyranosyl rings in 1 and 2, respectively, take a (4)C(1) chair conformation. In the crystal lattice, the 1-glucosamide 1 forms a symmetrical monolayer lipid membrane (MLM) structure in which the molecules are packed in an antiparallel fashion, while 1-galactosamide 2 has an unsymmetrical MLM with parallel molecular packing. The stereochemistry of the sugar hydroxy group proved to affect their hydrogen-bonding networks and induce the polymorphism of the MLM.     

Genome-wide application of RNAi to the discovery of potential drug targets

Progress is being made in the development of RNA interference-based (RNAi-based) strategies for the control of gene expression. It has been demonstrated that small interfering RNAs (siRNAs) can silence the expression of target genes in a sequence-specific manner in mammalian cells. Various groups, including our own, have developed systems for vector-mediated specific RNAi. Vector-based siRNA- (or shRNA) expression libraries directed against the entire human genome and siRNA libraries based on chemically synthesized oligonucleotides now allow the rapid identification of functional genes and potential drug targets. Use of such libraries will enhance our understanding of numerous biological phenomena and contribute to the rational design of drugs against heritable, infectious and malignant diseases.     

Electro-transfer of small interfering RNA ameliorated arthritis in rats

RNA interference provides the powerful means of sequence-specific gene silencing. Particularly, small interfering RNA (siRNA) duplexes may be potentially useful for therapeutic molecular targeting of human diseases, although novel delivery systems should be devised to achieve efficient and organ-specific transduction of siRNA. In the present study, we demonstrated that electro-transfer of a siRNA-polyamine complex made efficient and specific gene knockdown possible in the articular synovium. Targeted suppression of the tumor necrosis factor-alpha gene through this procedure significantly ameliorated collagen-induced arthritis in rats. Our results suggest the potential feasibility of therapeutic intervention with RNA medicines for treatment of rheumatoid and other locomotor diseases.