Isolation of an active catalytic core of Streptococcus downei MFe28 GTF-I glucosyltransferase

Truncated variants of GTF-I from Streptococcus downei MFe28 were purified by means of a histidine tag. Sequential deletions showed that the C-terminal domain was not directly involved in the catalytic process but was required for primer activation. A fully active catalytic core of only 100 kDa was isolated.     

Involvement of Gln937 of Streptococcus downei GTF-I glucansucrase in transition-state stabilization.

Multiple alignment of deduced amino-acid sequences of glucansucrases (glucosyltransferases and dextransucrases) from oral streptococci and Leuconostoc mesenteroides has shown them to share a well-conserved catalytic domain. A portion of this domain displays homology to members of the alpha-amylase family (glycoside hydrolase family 13), which all have a (beta/alpha)8 barrel structure. In the glucansucrases, however, the alpha-helix and beta-strand elements are circularly permuted with respect to the order in family 13. Previous work has shown that amino-acid residues contributing to the active site of glucansucrases are situated in structural elements that align with those of family 13. In alpha-amylase and cyclodextrin glucanotransferase, a histidine residue has been identified that acts to stabilize the transition state, and a histidine is conserved at the corresponding position in all other members of family 13. In all the glucansucrases, however, the aligned position is occupied by glutamine. Mutants of glucosyltransferase I were constructed in which this glutamine, Gln937, was changed to histidine, glutamic acid, aspartic acid, asparagine or alanine. The effects on specific activity, ability to form glucan and ability to transfer glucose to a maltose acceptor were examined. Only histidine could substitute for glutamine and maintain Michaelis-Menten kinetics, albeit at a greatly reduced kcat, showing that Gln937 plays a functionally equivalent role to the histidine in family 13. This provides additional evidence in support of the proposed alignment of the (beta/alpha)8 barrel structures. Mutation at position 937 altered the acceptor reaction with maltose, and resulted in the synthesis of novel gluco-oligosaccharides in which alpha1,3-linked glucosyl units are joined sequentially to maltose.     

丙型肝炎病毒高变区1中介导感染的关键氨基酸残基鉴定

丙型肝炎病毒( HCV)包膜E2蛋白氨基端的高变区1(HVR1)由27个氨基酸组成,是HCV蛋白中变异频率最高的肽段.HVR1含中和抗体表位,同时对HCV细胞侵入起重要作用,其结构与功能的关系目前尚不清楚.本研究对H77株包膜蛋白基因中的HVR1进行了一系列缺失突变,然后将突变体表达质粒与假病毒包装质粒共转染人胚肾(H...     

Identification of key amino acid residues in Neisseria polysaccharea amylosucrase

Amylosucrase from Neisseria polysaccharea catalyzes the synthesis of an amylose-like polymer from sucrose. Sequence alignment revealed that it belongs to the glycoside hydrolase family 13. Site-directed mutagenesis enabled the identification of functionally important amino acid residues located at the active center. Asp-294 is proposed to act as the catalytic nucleophile and Glu-336 as general acid base catalyst in amylosucrase. The conserved Asp-401, His-195 and His-400 residues are critical for the enzymatic activity. These results provide strong support for the predicted close structural and functional relationship between the sucrose-glucosyltransferases and enzymes of the alpha-amylase family.     

Identification of basic amino acids at the N-terminal end of the core protein that are crucial for hepatitis C virus infectivity

A major function of the hepatitis C virus (HCV) core protein is the interaction with genomic RNA to form the nucleocapsid, an essential component of the virus particle. Analyses to identify basic amino acid residues of HCV core protein, important for capsid assembly, were initially performed with a cell-free system, which did not indicate the importance of these residues for HCV infectivity. The development of a cell culture system for HCV (HCVcc) allows a more precise analysis of these core protein amino acids during the HCV life cycle. In the present study, we used a mutational analysis in the context of the HCVcc system to determine the role of the basic amino acid residues of the core protein in HCV infectivity. We focused our analysis on basic residues located in two clusters (cluster 1, amino acids [aa]6 to 23; cluster 2, aa 39 to 62) within the N-terminal 62 amino acids of the HCV core protein. Our data indicate that basic residues of the first cluster have little impact on replication and are dispensable for infectivity. Furthermore, only four basic amino acids residues of the second cluster (R50, K51, R59, and R62) were essential for the production of infectious viral particles. Mutation of these residues did not interfere with core protein subcellular localization, core protein-RNA interaction, or core protein oligomerization. Moreover, these mutations had no effect on core protein envelopment by intracellular membranes. Together, these data indicate that R50, K51, R59, and R62 residues play a major role in the formation of infectious viral particles at a post-nucleocapsid assembly step.     

Mass-spectrometric identification and sequence location of the ten residues of the new amino acid (gamma-Carboxyglutamic acid) in the N-terminal region of prothrombin.

The detailed mass-spectrometric evidence for our original findings [Magnusson et al. (1974) FEBS Lett. 44, 189-193] of ten gamma-carboxyglutamic acid residues in the N-terminal calcium-binding polypeptide of prothrombin is presented. The identification and sequence location of gamma-carboxyglutamic acid was made by electron-impact and field-desorption studies on acetyl permethyl peptide derivatives, and on the free amino acid. Details of the derivatives formed, and how this new amino acid may be easily recognized and sequenced from the mass spectrum, are given as a basis for future work.     

Isolation and N-terminal amino acid sequence of an octopamine ligand binding protein

An octopamine receptor photoaffinity probe was used to label membranes from the light organs of Photinus pyralis, a tissue highly enriched in octopamine receptors. Labeling was concentrated in a glycoprotein of 75 +/- 2 kDa with lesser labeling of a 79 +/- 2 kDa component. Labeling could be displaced by prior incubation with octopamine, mianserin, cyproheptadine, phentolamine or propranolol, with a relative potency that correlated with the ability of these same agents to modulate light organ octopamine-sensitive adenylate cyclase. The 75 kDa binding protein was isolated and its N-terminal amino acid sequence was determined.     

Action range of BMP is defined by its N-terminal basic amino acid core

During early development, cells receive positional information from neighboring cells to form tissue patterns in initially uniform germ layers. Ligands of the transforming growth factor (TGF-beta) superfamily are known to participate in this pattern formation. In particular, activin has been shown to act as a long-range dorsalizing signal to establish a concentration gradient in Xenopus. In contrast, BMP-2 and BMP-4, other members of the family, appear to influence and induce ventral fates only where they are expressed. This raises a question as to how the action of BMPs is tightly restricted to the region within and around the cells that produce them. Here, we have demonstrated that a basic core of only three amino acids in the N-terminal region of BMP-4 is required for its restriction to the non-neural ectoderm as its expression domain. Our results also suggest that heparan sulfate proteoglycans bind to this basic core and thus play a role in trapping BMP-4. The present study is the first to identify the critical domain of BMP that is responsible for its interaction with the extracellular environment that restricts its diffusion in vivo.     

N-terminal amino acid sequence of wheat proteins that lack phenylalanine and histidine residues.

The 24 residues of the N-terminal CNBr peptide from a wheat albumin, that lacks phenylalanine and histidine, have been sequenced. Three of the assignments were made partly by analogy with two other proteins, as evidence is presented that all three proteins are probably identical in this region. Extra evidence for the sequences of the alpha-chymotryptic peptides derived from the N-terminal CNBr peptides of the three proteins, and also for their assembly, has been deposited as Supplementary Publication SUP 50063 (11 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem J. (1976) 153, 5. The nature of such evidence is stated in the text of this present communication.     

Effects of removal of the N-terminal amino acid residues on the activity and conformation of firefly luciferase

A series of deletion mutants were constructed using polymerase chain reaction (PCR) to investigate the roles of luciferase N-terminal residues. The coding sequences of the first 0 (Luc0), 6 (Luc6), 7 (Luc7), 8 (Luc8), 9 (Luc9), 10 (Luc10) and 20 (Luc20) amino acids of the N-terminus were deleted and inserted into the prokaryotic expression vector pBV220. The results showed that the enzymes were completely inactivated when the first eight or more N-terminal amino acids were removed. The recombinant Luc0 and mutants Luc6 and Luc7 were purified to homogeneity by ammonium sulfate precipitation and liquid chromatography for determination of their activity and conformational changes. The activity assay showed that removal of the first six amino acids resulted in 29% loss of enzymatic activity while removal of the first seven amino acids resulted in nearly complete inactivation (with remaining activity <0.5% of the original activity). Circular dichroism spectra showed no significant secondary structure changes. But the fluorescence emission maximum red-shift indicated some conformational changes. Luc6 and Luc7 were more sensitive to guanidine unfolding than Luc0. The present result indicated the significant role of Ile7 to the luciferase stability.