scholarly journals Functional domains and interdomain communication in Candida albicans glucosamine-6-phosphate synthase

2007 ◽  
Vol 404 (1) ◽  
pp. 121-130 ◽  
Author(s):  
Jarosław Olchowy ◽  
Iwona Gabriel ◽  
Sławomir Milewski
Keyword(s):  
Candida Albicans ◽  
Kinetic Studies ◽  
Synthetic Activity ◽  
Protein Oligomerization ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
Bacterial Host ◽  
Feedback Inhibitor ◽  
Opening And Closing ◽  
Phosphate Synthase

Functional and structural properties of several truncated or mutated variants of Candida albicans Gfa1p (glucosamine-6-phosphate synthase) were compared with those of the wild-type enzyme. Fragments encompassing residues 1–345 and 346–712 of Gfa1p, expressed heterogeneously in bacterial host as His6 fusions, were identified as the functional GAH (glutamine amidehydrolysing) and ISOM (hexose phosphate-isomerizing) domains respectively. It was found that the native GAH domain is monomeric, whereas the native ISOM domain forms tetramers, as does the whole enzyme. Spectrofluorimetric and kinetic studies of the isolated domains, the Δ218–283Gfa1p mutein and the wild-type enzyme revealed that the binding site for the feedback inhibitor, uridine 5′-diphospho-N-acetyl-D-glucosamine, is located in the ISOM domain. Inhibitor binding affects amidohydrolysing activity of the GAH domain and, as a consequence, the GlcN-6-P (D-glucosamine-6-phosphate)-synthetic activity of the whole enzyme. The fragment containing residues 218–283 is neither involved in ligand binding nor in protein oligomerization. Comparison of the catalytic activities of Gfa1pV711F, Δ709–712Gfa1p, Gfa1pW97F and Gfa1pW97G with those of the native Gfa1p and the isolated domains provided evidence for an intramolecular channel connecting the GAH and ISOM domains of Gfa1p. The channel becomes leaky upon deletion of amino acids 709–712 and in the W97F and W97G mutants. The Trp97 residue was found to function as a molecular gate, opening and closing the channel. The W97G and V711F mutations resulted in an almost complete elimination of the GlcN-6-P-synthetic activity, with the retention of the amidohydrolase and sugar phosphate-isomerizing activities.

scholarly journals Elimination of 2-keto-3-deoxy-D-glycero-D-galacto-nonulosonic acid 9-phosphate synthase activity from human N-acetylneuraminic acid 9-phosphate synthase by a single mutation

2006 ◽  
Vol 397 (1) ◽  
pp. 195-201 ◽  
Author(s):  
Jijun Hao ◽  
Willie F. Vann ◽  
Stephan Hinderlich ◽  
Munirathinam Sundaramoorthy
Keyword(s):  
Aldol Condensation ◽  
Saturation Mutagenesis ◽  
Single Mutation ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
High Sequence Identity ◽  
Acetylneuraminic Acid ◽  
Nonulosonic Acid ◽  
The Impact ◽  
Phosphate Synthase

The most commonly occurring sialic acid Neu5Ac (N-acetylneuraminic acid) and its deaminated form, KDN (2-keto-3-deoxy-D-glycero-D-galacto-nonulosonic acid), participate in many biological functions. The human Neu5Ac-9-P (Neu5Ac 9-phosphate) synthase has the unique ability to catalyse the synthesis of not only Neu5Ac-9-P but also KDN-9-P (KDN 9-phosphate). Both reactions are catalysed by the mechanism of aldol condensation of PEP (phosphoenolpyruvate) with sugar substrates, ManNAc-6-P (N-acetylmannosamine 6-phosphate) or Man-6-P (mannose 6-phosphate). Mouse and putative rat Neu5Ac-9-P synthases, however, do not show KDN-9-P synthase activity, despite sharing high sequence identity (>95%) with the human enzyme. Here, we demonstrate that a single mutation, M42T, in human Neu5Ac-9-P synthase can abolish the KDN-9-P synthase activity completely without compromising the Neu5Ac-9-P synthase activity. Saturation mutagenesis of Met42 of the human Neu5Ac-9-P synthase showed that the substitution with all amino acids except leucine retains only the Neu5Ac-9-P synthase activity at levels comparable with the wild-type enzyme. The M42L mutant, like the wild-type enzyme, showed the additional KDN-9-P synthase activity. In the homology model of human Neu5Ac-9-P synthase, Met42 is located 22 Å (1 Å=0.1 nm) away from the substrate-binding site and the impact of this distant residue on the enzyme functions is discussed.

scholarly journals Structural and Biochemical Studies on the Regulation of Biotin Carboxylase by Substrate Inhibition and Dimerization

2011 ◽  
Vol 286 (27) ◽  
pp. 24417-24425 ◽  
Author(s):  
Chi-Yuan Chou ◽  
Liang Tong
Keyword(s):  
Binding Sites ◽  
Analytical Ultracentrifugation ◽  
Substrate Inhibition ◽  
Kinetic Studies ◽  
The Other ◽  
Biotin Carboxylase ◽  
Binding Modes ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
Dimer Interface

Biotin carboxylase (BC) activity is shared among biotin-dependent carboxylases and catalyzes the Mg-ATP-dependent carboxylation of biotin using bicarbonate as the CO2 donor. BC has been studied extensively over the years by structural, kinetic, and mutagenesis analyses. Here we report three new crystal structures of Escherichia coli BC at up to 1.9 Å resolution, complexed with different ligands. Two structures are wild-type BC in complex with two ADP molecules and two Ca2+ ions or two ADP molecules and one Mg2+ ion. One ADP molecule is in the position normally taken by the ATP substrate, whereas the other ADP molecule occupies the binding sites of bicarbonate and biotin. One Ca2+ ion and the Mg2+ ion are associated with the ADP molecule in the active site, and the other Ca2+ ion is coordinated by Glu-87, Glu-288, and Asn-290. Our kinetic studies confirm that ATP shows substrate inhibition and that this inhibition is competitive against bicarbonate. The third structure is on the R16E mutant in complex with bicarbonate and Mg-ADP. Arg-16 is located near the dimer interface. The R16E mutant has only a 2-fold loss in catalytic activity compared with the wild-type enzyme. Analytical ultracentrifugation experiments showed that the mutation significantly destabilized the dimer, although the presence of substrates can induce dimer formation. The binding modes of bicarbonate and Mg-ADP are essentially the same as those to the wild-type enzyme. However, the mutation greatly disrupted the dimer interface and caused a large re-organization of the dimer. The structures of these new complexes have implications for the catalysis by BC.

scholarly journals Investigation of putative active-site lysine residues in hydroxymethylbilane synthase. Preparation and characterization of mutants in which (a) Lys-55, (b) Lys-59 and (c) both Lys-55 and Lys-59 have been replaced by glutamine

1990 ◽  
Vol 271 (2) ◽  
pp. 487-491 ◽  
Author(s):  
A Hädener ◽  
P R Alefounder ◽  
G J Hart ◽  
C Abell ◽  
A R Battersby
Keyword(s):  
Escherichia Coli ◽  
Active Site ◽  
Kinetic Studies ◽  
Enzyme Kinetic ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
Over Expression ◽  
Putative Active Site ◽  
Lysine Residues

A new construct carrying the hemC gene was transformed into Escherichia coli, resulting in approx. 1000-fold over-expression of hydroxymethylbilane synthase (HMBS). This construct was used to generate HMBS in which (a) Lys-55, (b) Lys-59 and (c) both Lys-55 and Lys-59 were replaced by glutamine (K55Q, K59Q and K55Q-K59Q respectively). All three modified enzymes are chromatographically separable from wild-type enzyme. Kinetic studies showed that the substitution K55Q has little effect whereas K59Q causes a 25-fold decrease in Kapp. cat./Kapp. m. Treatment of K55Q, K59Q and K55Q-K59Q separately with pyridoxal 5′-phosphate and NaBH4 resulted in incomplete and non-specific reaction with the remaining lysine residues. Pyridoxal modification of Lys-59 in the K55Q mutant caused greater enzymic inactivation than similar modification of Lys-55 in K59Q. The results in sum show that, though Lys-55 and Lys-59 may be at or near the active site, neither is indispensable for the catalytic activity of HMBS.

scholarly journals Improving the Thermostability and Catalytic Efficiency of Bacillus deramificans Pullulanase by Site-Directed Mutagenesis

2013 ◽  
Vol 79 (13) ◽  
pp. 4072-4077 ◽  
Author(s):  
Xuguo Duan ◽  
Jian Chen ◽  
Jing Wu
Keyword(s):  
Catalytic Efficiency ◽  
Kinetic Studies ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
Ph Optimum ◽  
Widespread Application ◽  
Content Type ◽  
Major Factors

ABSTRACTPullulanase (EC 3.2.1.41) is a well-known starch-debranching enzyme. Its instability and low catalytic efficiency are the major factors preventing its widespread application. To address these issues, Asp437 and Asp503 of the pullulanase fromBacillus deramificanswere selected in this study as targets for site-directed mutagenesis based on a structure-guided consensus approach. Four mutants (carrying the mutations D503F, D437H, D503Y, and D437H/D503Y) were generated and characterized in detail. The results showed that the D503F, D437H, and D503Y mutants had an optimum temperature of 55°C and a pH optimum of 4.5, similar to that of the wild-type enzyme. However, the half-lives of the mutants at 60°C were twice as long as that of the wild-type enzyme. In addition, the D437H/D503Y double mutant displayed a larger shift in thermostability, with an optimal temperature of 60°C and a half-life at 60°C of more than 4.3-fold that of the wild-type enzyme. Kinetic studies showed that theKmvalues for the D503F, D437H, D503Y, and D437H/D503Y mutants decreased by 7.1%, 11.4%, 41.4%, and 45.7% and theKcat/Kmvalues increased by 10%, 20%, 140%, and 100%, respectively, compared to those of the wild-type enzyme. Mechanisms that could account for these enhancements were explored. Moreover, in conjunction with the enzyme glucoamylase, the D503Y and D437H/D503Y mutants exhibited an improved reaction rate and glucose yield during starch hydrolysis compared to those of the wild-type enzyme, confirming the enhanced properties of the mutants. The mutants generated in this study have potential applications in the starch industry.

scholarly journals Disruption of the Candida albicans TPS1Gene Encoding Trehalose-6-Phosphate Synthase Impairs Formation of Hyphae and Decreases Infectivity

1998 ◽  
Vol 180 (15) ◽  
pp. 3809-3815 ◽  
Author(s):  
Oscar Zaragoza ◽  
Miguel A. Blazquez ◽  
Carlos Gancedo
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Candida Albicans ◽  
Type Strain ◽  
Wild Type Strain ◽  
Calf Serum ◽  
Sugar Metabolism ◽  
Functional Complementation ◽  
Wild Type ◽  
Growth Defects ◽  
Phosphate Synthase

ABSTRACT The TPS1 gene from Candida albicans, which encodes trehalose-6-phosphate synthase, has been cloned by functional complementation of a tps1 mutant from Saccharomyces cerevisiae. In contrast with the wild-type strain, the doubletps1/tps1 disruptant did not accumulate trehalose at stationary phase or after heat shock. Growth of thetps1/tps1 disruptant at 30°C was indistinguishable from that of the wild type. However, at 42°C it did not grow on glucose or fructose but grew normally on galactose or glycerol. At 37°C, the yeast-hypha transition in the mutant in glucose-calf serum medium did not occur. During growth at 42°C, the mutant did not form hyphae in galactose or in glycerol. Some of the growth defects observed may be traced to an unbalanced sugar metabolism that reduces the cellular content of ATP. Mice inoculated with 106 CFU of thetps1/tps1 mutant did not show visible symptoms of infection 16 days after inoculation, while those similarly inoculated with wild-type cells were dead 12 days after inoculation.

scholarly journals Relevant Double Mutations in Bioengineered Streptomyces clavuligerus Deacetoxycephalosporin C Synthase Result in Higher Binding Specificities Which Improve Penicillin Bioconversion

2007 ◽  
Vol 74 (4) ◽  
pp. 1167-1175 ◽  
Author(s):  
Kian Sim Goo ◽  
Chun Song Chua ◽  
Tiow-Suan Sim
Keyword(s):  
Substrate Binding ◽  
Kinetic Studies ◽  
Streptomyces Clavuligerus ◽  
Penicillin G ◽  
Binding Affinities ◽  
Amino Acid Residues ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
Type Activity ◽  
Insight Into

ABSTRACT Streptomyces clavuligerus deacetoxycephalosporin C synthase (ScDAOCS) is an important industrial enzyme for the production of 7-aminodeacetoxycephalosporanic acid, which is a precursor for cephalosporin synthesis. Single mutations of six amino acid residues, V275, C281, N304, I305, R306, and R307, were previously shown to result in enhanced levels of ampicillin conversion, with activities ranging from 129 to 346% of the wild-type activity. In this study, these mutations were paired to investigate their effects on enzyme catalysis. The bioassay results showed that the C-terminal mutations (N304X [where X is alanine, leucine, methionine, lysine, or arginine], I305M, R306L, and R307L) in combination with C281Y substantially increased the conversion of ampicillin; the activity was up to 491% of the wild-type activity. Similar improvements were observed for converting carbenicillin (up to 1,347% of the wild-type activity) and phenethicillin (up to 1,109% of the wild-type activity). Interestingly, the N304X R306L double mutants exhibited lower activities for penicillin G conversion, and activities that were 40 to 114% of wild-type enzyme activity were detected. Based on kinetic studies using ampicillin, it was clear that the increases in the activities of the double mutants relative to those of the corresponding single mutants were due to enhanced substrate binding affinities. These results also validated the finding that the N304R and I305M mutations are ideal for increasing the substrate binding affinity and turnover rate of the enzyme, respectively. This study provided further insight into the structure-function interaction of ScDAOCS with different penicillin substrates, thus providing a useful platform for further rational modification of its enzymatic properties.

Enhancement of Acid Stability of Alpha Amylase from Bacillus licheniformis by Error-Prone PCR

2013 ◽  
Vol 774-776 ◽  
pp. 664-669
Author(s):  
Yan Jing Xu ◽  
Yi Han Liu ◽  
Shuai Fan ◽  
Fu Ping Lu
Keyword(s):  
Bacillus Licheniformis ◽  
Double Mutant ◽  
Kinetic Studies ◽  
Site Directed Mutagenesis ◽  
Alpha Amylase ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
Chain Reaction ◽  
Acid Stability ◽  
Polymerase Chain

Acid stability of Bacillus licheniformis alpha amylase (BLA) was improved by error-prone polymerase chain reaction. The mutated BLA gene was expressed in Escherichia coli. An acid stability double mutant (K344R/H405R in BLA) was isolated. Two single mutants K344R and H405R were obtained by the way of site-directed mutagenesis. The enzymes (BLA) of the three mutants were isolated and characterized. Kinetic studies showed that the kcat/Km values of the mutants K344R, H405R, and K344R/H405R under pH 4.5 were about 8-, 11.5-, and 17.7-times higher than that of the wild type enzyme. As revealed by the structure models of the wild-type and mutant enzymes, the amino acids substituted of R344 and R405 in the BLA contribute to its acid stability.

scholarly journals Spectroscopic and Kinetic Studies of Y114F and W116F Mutants of Me2SO Reductase from Rhodobacter capsulatus

2007 ◽  
Vol 282 (49) ◽  
pp. 35519-35529 ◽  
Author(s):  
Nathan Cobb ◽  
Craig Hemann ◽  
Gregory A. Polsinelli ◽  
Justin P. Ridge ◽  
Alastair G. McEwan ◽  
...  
Keyword(s):  
Rhodobacter Capsulatus ◽  
Kinetic Studies ◽  
Sodium Dithionite ◽  
Wild Type ◽  
Active Site Residues ◽  
Oxygen Atom Transfer ◽  
Wild Type Enzyme ◽  
Long Wavelength ◽  
Coordinate Form ◽  
Group Reduction

Mutants of the active site residues Trp-116 and Tyr-114 of the molybdenum-containing Me2SO reductase from Rhodobacter capsulatus have been examined spectroscopically and kinetically. The Y114F mutant has an increased rate constant for oxygen atom transfer from Me2SO to reduced enzyme, the result of lower stability of the Ered·Me2SO complex. The absorption spectrum of this species (but not that of either oxidized or reduced enzyme) is significantly perturbed in the mutant relative to wild-type enzyme, consistent with Tyr-114 interacting with bound Me2SO. The as-isolated W116F mutant is only five-coordinate, with one of the two equivalents of the pyranopterin cofactor found in the enzyme dissociated from the molybdenum and replaced by a second MoO group. Reduction of the mutant with sodium dithionite and reoxidation with Me2SO, however, regenerates the long-wavelength absorbance of functional enzyme, although the wavelength maximum is shifted to 670 nm from the 720 nm of wild-type enzyme. This “redox-cycled” mutant exhibits a Me2SO reducing activity and overall reaction mechanism similar to that of wild-type enzyme but rapidly reverts to the inactive five-coordinate form in the course of turnover.

scholarly journals GDP-mannose pyrophosphorylase is essential in the bloodstream form of Trypanosoma brucei

2010 ◽  
Vol 425 (3) ◽  
pp. 603-614 ◽  
Author(s):  
Helen Denton ◽  
Stewart Fyffe ◽  
Terry K. Smith
Keyword(s):  
Trypanosoma Brucei ◽  
Drug Target ◽  
Kinetic Studies ◽  
Bloodstream Form ◽  
Surface Glycoprotein ◽  
Mrna Levels ◽  
Wild Type ◽  
Cell Surface Glycoprotein ◽  
Catalytically Active ◽  
Feedback Inhibitor

A putative GDP-Man PP (guanidine diphosphomannose pyrophosphorylase) gene from Trypanosoma brucei (TbGDP-Man PP) was identified in the genome and subsequently cloned, sequenced and recombinantly expressed, and shown to be a catalytically active dimer. Kinetic analysis revealed a Vmax of 0.34 μmol/min per mg of protein and Km values of 67 μM and 12 μM for GTP and mannose 1-phosphate respectively. Further kinetic studies showed GDP-Man was a potent product feedback inhibitor. RNAi (RNA interference) of the cytosolic TbGDP-Man PP showed that mRNA levels were reduced to ~20% of wild-type levels, causing the cells to die after 3–4 days, demonstrating that TbGDP-Man PP is essential in the bloodstream form of T. brucei and thus a potential drug target. The RNAi-induced parasites have a greatly reduced capability to form GDP-Man, leading ultimately to a reduction in their ability to synthesize their essential GPI (glycosylphosphatidylinositol) anchors. The RNAi-induced parasites also showed aberrant N-glycosylation of their major cell-surface glycoprotein, variant surface glycoprotein, with loss of the high-mannose Man9GlcNAc2 N-glycosylation at Asn428 and formation of complex N-glycans at Asn263.

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