Variations in Both TG1 and TG2 Isozyme-specific In Situ Activities and Protein Expressions during Mouse Embryonic Development

Transglutaminase (TG) is a family of enzymes that catalyzes cross-linking reactions among proteins. Using fluorescent-labeled highly reactive substrate peptides, we recently developed a system to visualize isozyme-specific in situ enzymatic activity. In the present study, we investigated the in situ activities of TG1 (skin-type) and TG2 (tissue-type) using whole mouse sections of various embryonic developmental stages and neonates. In each case, we also successfully used immunostaining of identical whole mouse sections for protein expression after detection of enzymatic activities. In general, the enzymatic activity was correlated with TG protein expression. However, in some tissues, TG protein expression patterns, which were inconsistent with the enzymatic activities, suggested that inactive TGs were produced possibly by self cross-linking or other modifications. Our method allowed us to simultaneously observe developmental variations in both TG isozyme-specific activities and protein levels in mouse embryonic and neonate tissues.     

Are entrenched characters developmentally constrained? Creating biramous limbs in an insect

SUMMARY Are evolutionarily entrenched phenotypes highly constrained developmentally? We explored this question in the case of the uniramous appendages of fruit flies. We created bi‐ and polyramous antenna/leg combinations in four different genotypes. Each genotype consisted of two relevant mutations. We suggest that not all entrenched characters are strongly constrained by developmental processes and that there exists sufficient natural genetic variation to alter highly conserved phenotypes.     

Cis-dichlorodiammineplatinum(II) has a binding specificity for adjoining guanine bases

Self complementary deoxyribooctanucleotides, [5′-d(GpGpTpCpGpApCpC)-3′]₂ and [5’-d(CpGpGp- ApTpCpCpG)-3’]₂, were allowed to react with cis- PtCl₂(NH₃)₂, and the reaction mixture was treated with exonuclease (snake venom phosphodiesterase and/or calf spleen phosphodiesterase). Semi-quantitative analysis by HPLC showed that the adjoining guanine bases have a specific binding affinity to cis-PtCl₂(NH₃)₂.     

Monoubiquitylation of GGA3 by hVPS18 regulates its ubiquitin-binding ability

GGAs (Golgi-localizing, gamma-adaptin ear domain homology, ADP-ribosylation factor (ARF)-binding proteins), constitute a family of monomeric adaptor proteins and are associated with protein trafficking from the trans-Golgi network to endosomes. Here, we show that GGA3 is monoubiquitylated by a RING-H2 type-ubiquitin ligase hVPS18 (human homologue of vacuolar protein sorting 18). By in vitro ubiquitylation assays, we have identified lysine 258 in the GAT domain as a major ubiquitylation site that resides adjacent to the ubiquitin-binding site. The ubiquitylation is abolished by a mutation in either the GAT domain or ubiquitin that disrupts the GAT-ubiquitin interaction, indicating that the ubiquitin binding is a prerequisite for the ubiquitylation. Furthermore, the GAT domain ubiquitylated by hVPS18 no longer binds to ubiquitin, indicating that ubiquitylation negatively regulates the ubiquitin-binding ability of the GAT domain. These results suggest that the ubiquitin binding and ubiquitylation of GGA3-GAT domain are mutually inseparable through a ubiquitin ligase activity of hVPS18.     

The transmembrane domain directs TLR9 to intracellular compartments that contain TLR3

Toll-like receptors (TLRs) are type I transmembrane (TM) proteins indispensable for sensing microbial and viral infection. Despite their conserved primary structures, some TLRs that detect pathogen-derived nucleic acids (TLR3, TLR7, TLR8, and TLR9) are retained in the cytoplasm. The intracellular localization of TLR9 is important for its ability to discriminate self- and non-self DNA, but the mechanism by which it is retained in the cytoplasm is unclear. In the present study, we found that the TM domain of TLR9 directs its intracellular localization. The TM domain of TLR9 also targets CD25, a heterologous type I TM protein, to intracellular compartments that contain TLR9. We also found that TLR9 generally co-localizes with TLR3, although its linker region, not its TM domain, directs intracellular localization of TLR3. These data demonstrate that the TM domain of TLR9 is a critical regulatory element that targets TLR9 to its intracellular location.     

Purification and characterization of an alpha-amylase of Pichia burtonii isolated from the traditional starter "murcha" in Nepal

Among more than 20 yeast strains isolated from the traditional starter "murcha" in Nepal, we characterized a yeast that might be involved in saccharification. This strain, identified as Pichia burtonii, produced an extracellular amylolytic enzyme when cultured in the presence of starch in the medium. Since no amylase secreted by P. burtonii has yet been reported, we purified the enzyme and determined its N-terminal amino acid sequence. Together with the results of a hydrolyzing activity assay toward various substrates, it was found to be an alpha-amylase. The purified enzyme, named Pichia burtonii alpha-amylase (PBA), was a glycoprotein with an apparent molecular mass of 51 kDa. Enzyme activity was optimal at pH 5.0 at 40 degrees C. The enzyme retained 80% of its original activity after incubation under the optimal pH condition at 50 degrees C for 30 min. The activity was inhibited by metal ions such as Cd(2+), Cu(2+), Hg(2+), Al(3+), and Zn(2+).     

Integrin alphaIIbbeta3 induces the adhesion and activation of mast cells through interaction with fibrinogen

Integrin alphaIIb, a well-known marker of megakaryocyte-platelet lineage, has been recently recognized on hemopoietic progenitors. We now demonstrate that integrin alphaIIbbeta3 is highly expressed on mouse and human mast cells including mouse bone marrow-derived mast cells, peritoneal mast cells, and human cord blood-derived mast cells, and that its binding to extracellular matrix proteins leads to enhancement of biological functions of mast cells in concert with various stimuli. With exposure to various stimuli, including cross-linking of FcepsilonRI and stem cell factor, mast cells adhered to extracellular matrix proteins such as fibrinogen and von Willebrand factor in an integrin alphaIIbbeta3-dependent manner. In addition, the binding of mast cells to fibrinogen enhanced proliferation, cytokine production, and migration and induced uptake of soluble fibrinogen in response to stem cell factor stimulation, implicating integrin alphaIIbbeta3 in a variety of mast cell functions. In conclusion, mouse and human mast cells express functional integrin alphaIIbbeta3.     

Structural basis of carbohydrate transfer activity by human UDP-GalNAc: polypeptide alpha-N-acetylgalactosaminyltransferase (pp-GalNAc-T10)

Mucin-type O-glycans are important carbohydrate chains involved in differentiation and malignant transformation. Biosynthesis of the O-glycan is initiated by the transfer of N-acetylgalactosamine (GalNAc) which is catalyzed by UDP-GalNAc:polypeptide alpha-N-acetylgalactosaminyltransferases (pp-GalNAc-Ts). Here we present crystal structures of the pp-GalNAc-T10 isozyme, which has specificity for glycosylated peptides, in complex with the hydrolyzed donor substrate UDP-GalNAc and in complex with GalNAc-serine. A structural comparison with uncomplexed pp-GalNAc-T1 suggests that substantial conformational changes occur in two loops near the catalytic center upon donor substrate binding, and that a distinct interdomain arrangement between the catalytic and lectin domains forms a narrow cleft for acceptor substrates. The distance between the catalytic center and the carbohydrate-binding site on the lectin beta sub-domain influences the position of GalNAc glycosylation on GalNAc-glycosylated peptide substrates. A chimeric enzyme in which the two domains of pp-GalNAc-T10 are connected by a linker from pp-GalNAc-T1 acquires activity toward non-glycosylated acceptors, identifying a potential mechanism for generating the various acceptor specificities in different isozymes to produce a wide range of O-glycans.