scholarly journals Site-Directed Mutagenesis of the Anabaena sp. Strain PCC 7120 Nitrogenase Active Site To Increase Photobiological Hydrogen Production

2010 ◽  
Vol 76 (20) ◽  
pp. 6741-6750 ◽  
Author(s):  
Hajime Masukawa ◽  
Kazuhito Inoue ◽  
Hidehiro Sakurai ◽  
C. Peter Wolk ◽  
Robert P. Hausinger
Keyword(s):  
Active Site ◽  
Electron Flow ◽  
Hydrogen Gas ◽  
Site Directed Mutagenesis ◽  
Amino Acid Residues ◽  
Proton Reduction ◽  
Anabaena Sp ◽  
Pcc 7120 ◽  
Iron Molybdenum Cofactor

ABSTRACT Cyanobacteria use sunlight and water to produce hydrogen gas (H2), which is potentially useful as a clean and renewable biofuel. Photobiological H2 arises primarily as an inevitable by-product of N2 fixation by nitrogenase, an oxygen-labile enzyme typically containing an iron-molybdenum cofactor (FeMo-co) active site. In Anabaena sp. strain 7120, the enzyme is localized to the microaerobic environment of heterocysts, a highly differentiated subset of the filamentous cells. In an effort to increase H2 production by this strain, six nitrogenase amino acid residues predicted to reside within 5 � of the FeMo-co were mutated in an attempt to direct electron flow selectively toward proton reduction in the presence of N2. Most of the 49 variants examined were deficient in N2-fixing growth and exhibited decreases in their in vivo rates of acetylene reduction. Of greater interest, several variants examined under an N2 atmosphere significantly increased their in vivo rates of H2 production, approximating rates equivalent to those under an Ar atmosphere, and accumulated high levels of H2 compared to the reference strains. These results demonstrate the feasibility of engineering cyanobacterial strains for enhanced photobiological production of H2 in an aerobic, nitrogen-containing environment.

scholarly journals HetF and PatA Control Levels of HetR in Anabaena sp. Strain PCC 7120

2008 ◽  
Vol 190 (23) ◽  
pp. 7645-7654 ◽  
Author(s):  
Douglas D. Risser ◽  
Sean M. Callahan
Keyword(s):  
Active Site ◽  
Transcriptional Activity ◽  
Inverse Correlation ◽  
Inducible Promoter ◽  
Site Directed Mutagenesis ◽  
Filamentous Cyanobacterium ◽  
Transcription Start ◽  
Anabaena Sp ◽  
Pcc 7120 ◽  
Active Site Histidine

ABSTRACT Anabaena sp. strain PCC 7120 is a filamentous cyanobacterium that differentiates heterocysts in response to deprivation of combined nitrogen. A hetF deletion strain lacked heterocysts and had aberrant cell morphology. Site-directed mutagenesis of the predicted active-site histidine and cysteine residues of this putative caspase-hemoglobinase fold protease abolished HetF function, supporting the hypothesis that HetF is a protease. Deletion of patA, which is necessary for the formation of most intercalary heterocysts, or hetF resulted in an increase in HetR protein, and extra copies of hetF on a plasmid functionally bypassed the deletion of patA. A hetR-gfp translational fusion expressed from an inducible promoter demonstrated that hetF-dependent downregulation of HetR levels occurs rapidly in vegetative cells, as well as developing heterocysts. “Mosaic” filaments in which only one cell of a filament had a copy of hetR or hetF indicated that hetF is required for differentiation only in cells that will become heterocysts. hetF was required for transcription from a hetR-dependent transcription start point of the hetR promoter and induction of transcription from the patS promoter. The inverse correlation between the level of HetR protein and transcription from hetR-dependent promoters suggests that the transcriptional activity of HetR is regulated by HetF and PatA.

scholarly journals Identification of Active Site Residues of the Siderophore Synthesis Enzyme PvdF and Evidence for Interaction of PvdF with a Substrate-Providing Enzyme

2021 ◽  
Vol 22 (4) ◽  
pp. 2211
Author(s):  
Priya Philem ◽  
Torsten Kleffmann ◽  
Sinan Gai ◽  
Bill C. Hawkins ◽  
Sigurd M. Wilbanks ◽  
...  
Keyword(s):  
Enzymatic Activity ◽  
Active Site ◽  
Opportunistic Pathogen ◽  
Site Directed Mutagenesis ◽  
Amino Acid Residues ◽  
Active Site Residues ◽  
Infection Models ◽  
Key Factor

The problematic opportunistic pathogen Pseudomonas aeruginosa secretes a siderophore, pyoverdine. Pyoverdine scavenges iron needed by the bacteria for growth and for pathogenicity in a range of different infection models. PvdF, a hydroxyornithine transformylase enzyme, is essential for pyoverdine synthesis, catalysing synthesis of formylhydroxyornithine (fOHOrn) that forms part of the pyoverdine molecule and provides iron-chelating hydroxamate ligands. Using a mass spectrometry assay, we confirm that purified PvdF catalyses synthesis of fOHOrn from hydroxyornithine and formyltetrahydrofolate substrates. Site directed mutagenesis was carried out to investigate amino acid residues predicted to be required for enzymatic activity. Enzyme variants were assayed for activity in vitro and also in vivo, through measuring their ability to restore pyoverdine production to a pvdF mutant strain. Variants at two putative catalytic residues N168 and H170 greatly reduced enzymatic activity in vivo though did not abolish activity in vitro. Change of a third residue D229 abolished activity both in vivo and in vitro. A change predicted to block entry of N10-formyltetrahydrofolate (fTHF) to the active site also abolished activity both in vitro and in vivo. A co-purification assay showed that PvdF binds to an enzyme PvdA that catalyses synthesis of hydroxyornithine, with this interaction likely to increase the efficiency of fOHOrn synthesis. Our findings advance understanding of how P. aeruginosa synthesises pyoverdine, a key factor in host–pathogen interactions.

scholarly journals ADP-Ribose-1"-Monophosphatase: a Conserved Coronavirus Enzyme That Is Dispensable for Viral Replication in Tissue Culture

2005 ◽  
Vol 79 (20) ◽  
pp. 12721-12731 ◽  
Author(s):  
Ákos Putics ◽  
Witold Filipowicz ◽  
Jonathan Hall ◽  
Alexander E. Gorbalenya ◽  
John Ziebuhr
Keyword(s):  
Active Site ◽  
Biological Significance ◽  
Virus Titer ◽  
Site Directed Mutagenesis ◽  
Replicase Gene ◽  
Active Site Residues ◽  
Nonstructural Proteins ◽  
Trna Splicing

ABSTRACT Replication of the ∼30-kb plus-strand RNA genome of coronaviruses and synthesis of an extensive set of subgenome-length RNAs are mediated by the replicase-transcriptase, a membrane-bound protein complex containing several cellular proteins and up to 16 viral nonstructural proteins (nsps) with multiple enzymatic activities, including protease, polymerase, helicase, methyltransferase, and RNase activities. To get further insight into the replicase gene-encoded functions, we characterized the coronavirus X domain, which is part of nsp3 and has been predicted to be an ADP-ribose-1"-monophosphate (Appr-1"-p) processing enzyme. Bacterially expressed forms of human coronavirus 229E (HCoV-229E) and severe acute respiratory syndrome-coronavirus X domains were shown to dephosphorylate Appr-1"-p, a side product of cellular tRNA splicing, to ADP-ribose in a highly specific manner. The enzyme had no detectable activity on several other nucleoside phosphates. Guided by the crystal structure of AF1521, an X domain homolog from Archaeoglobus fulgidus, potential active-site residues of the HCoV-229E X domain were targeted by site-directed mutagenesis. The data suggest that the HCoV-229E replicase polyprotein residues, Asn 1302, Asn 1305, His 1310, Gly 1312, and Gly 1313, are part of the enzyme's active site. Characterization of an Appr-1"-pase-deficient HCoV-229E mutant revealed no significant effects on viral RNA synthesis and virus titer, and no reversion to the wild-type sequence was observed when the mutant virus was passaged in cell culture. The apparent dispensability of the conserved X domain activity in vitro indicates that coronavirus replicase polyproteins have evolved to include nonessential functions. The biological significance of the novel enzymatic activity in vivo remains to be investigated.

scholarly journals Identification of Essential Residues in Apolipoprotein N-Acyl Transferase, a Member of the CN Hydrolase Family

2007 ◽  
Vol 189 (12) ◽  
pp. 4456-4464 ◽  
Author(s):  
Dominique Vidal-Ingigliardi ◽  
Shawn Lewenza ◽  
Nienke Buddelmeijer
Keyword(s):  
Active Site ◽  
Structural Model ◽  
Protein Structures ◽  
Catalytic Triad ◽  
Site Directed Mutagenesis ◽  
Acyl Transferase ◽  
Active Site Residues ◽  
Flexible Arms ◽  
Hydrolase Family

ABSTRACT Apolipoprotein N-acyl transferase (Lnt) is an essential membrane-bound protein involved in lipid modification of all lipoproteins in gram-negative bacteria. Essential residues in Lnt of Escherichia coli were identified by using site-directed mutagenesis and an in vivo complementation assay. Based on sequence conservation and known protein structures, we predict a model for Lnt, which is a member of the CN hydrolase family. Besides the potential catalytic triad E267-K335-C387, four residues that directly affect the modification of Braun's lipoprotein Lpp are absolutely required for Lnt function. Residues Y388 and E389 are part of the hydrophobic pocket that constitutes the active site. Residues W237 and E343 are located on two flexible arms that face away from the active site and are expected to open and close upon the binding and release of phospholipid and/or apolipoprotein. Substitutions causing temperature-dependent effects were located at different positions in the structural model. These mutants were not affected in protein stability. Lnt proteins from other proteobacteria, but not from actinomycetes, were functional in vivo, and the essential residues identified in Lnt of E. coli are conserved in these proteins.

PROTECTION BY α1-ANTITRYPSIN ALA-357 ARG-358 AGAINST ARTERIAL HYPOTENSION INDUCED BY FACTOR XII FRAGMENT

1987 ◽  
Author(s):  
M Schapira ◽  
B Waeber ◽  
H R Brunner ◽  
R Crystal ◽  
M Courtney
Keyword(s):  
Therapeutic Potential ◽  
Site Directed Mutagenesis ◽  
Factor Xii ◽  
Thrombin Time ◽  
Amino Acid Residues ◽  
Disease States ◽  
Blood Pressure Fall ◽  
Reactive Center ◽  
Male Wistar Rats

The specificity of serine protease inhibitors belonging to the serpin superfamily depends on the nature of the reactive center amino acid residues. For example, Met→Arg mutation at the reactive center P1 residue (position 358) alters the specificity of α1-antitrypsin (AT) from the Met-specific enzyme neutrophil elastase to the Arg-specific proteases thrombin, plasma kallikrein (K) and activated Factor XII fragment (XIIf). To obtain an inhibitor species which would inhibit K and XIIf but not thrombin, we now have produced by site-directed mutagenesis of cloned AT cDNA an AT variant having Arg at P1 and Ala at P2. This modification at P2 was made because C1-inhibitor, the major inhibitor of K and XIIf, also has Ala at P2. In purified systems, AT Ala-357 Arg-358 inactivated thrombin, K and XIIf with 2nd-order rate constants of 1.1, 21.8 and 0.6 μM-1 min-1 whereas values of 8.5, 4.2 and 2.1 μM-1 min-1 were found with AT Arg-358. Thus, when compared to AT Arg-358, AT Ala-357 Arg-358 was 5.2 times more efficient for inhibiting K but 7.7 times less efficient for inhibiting thrombin. In vivo, AT Ala-357 Arg-358 (0.7 mg i.v.) did not modify the thrombin time of male Wistar rats while a 2-fold prolongation was seen with 0.7 mg AT Arg-358. However, AT Ala-357 Arg-358 (0.7 mg i.v.) partially prevented the kinin-mediated circulatory collapse induced by XIIf (0.1 μg i.v.) since rats (n=4) treated with this double mutant had a blood pressure fall of 14 ±3 (meaniSD) mmHg while control animals (n = 8) receiving saline or AT Val-358 (0.7 mg i.v.) had a decrease of 27 ± 3 mmHg (p<0.01 by t test). AT Ala-357 Arg-358 has therapeutic potential for disease states with activation of the plasma kinin-forming system such as angioedema attacks or septic shock.

Site-directed mutagenesis and spectral studies suggest a putative role of FurA from Anabaena sp. PCC 7120 as a heme sensor protein

FEBS Journal ◽  
2012 ◽  
Vol 279 (12) ◽  
pp. 2231-2246 ◽  
Author(s):  
Silvia Pellicer ◽  
Andrés González ◽  
M. Luisa Peleato ◽  
Jesús I. Martinez ◽  
María F. Fillat ◽  
...  
Keyword(s):  
Site Directed Mutagenesis ◽  
Spectral Studies ◽  
Directed Mutagenesis ◽  
Putative Role ◽  
Sensor Protein ◽  
Anabaena Sp ◽  
Pcc 7120

scholarly journals Biosensors-Based In Vivo Quantification of 2-Oxoglutarate in Cyanobacteria and Proteobacteria

Life ◽  
2018 ◽  
Vol 8 (4) ◽  
pp. 51 ◽  
Author(s):  
Hai-Lin Chen ◽  
Amel Latifi ◽  
Cheng-Cai Zhang ◽  
Christophe Bernard
Keyword(s):  
Conformational Changes ◽  
Nitrogen Assimilation ◽  
Krebs Cycle ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Cellular Level ◽  
Cyanobacterium Anabaena ◽  
Anabaena Sp ◽  
Pcc 7120

2-oxoglutarate (α-ketoglutarate; 2-OG) is an intermediate of the Krebs cycle, and constitutes the carbon skeleton for nitrogen assimilation and the synthesis of a variety of compounds. In addition to being an important metabolite, 2-OG is a signaling molecule with a broad regulatory repertoire in a variety of organisms, including plants, animals, and bacteria. Although challenging, measuring the levels and variations of metabolic signals in vivo is critical to better understand how cells control specific processes. To measure cellular 2-OG concentrations and dynamics, we designed a set of biosensors based on the fluorescence resonance energy transfer (FRET) technology that can be used in vivo in different organisms. For this purpose, we took advantage of the conformational changes of two cyanobacterial proteins induced by 2-OG binding. We show that these biosensors responded immediately and specifically to different 2-OG levels, and hence allowed to measure 2-OG variations in function of environmental modifications in the proteobacterium Escherichia coli and in the cyanobacterium Anabaena sp. PCC 7120. Our results pave the way to study 2-OG dynamics at the cellular level in uni- and multi-cellular organisms.

scholarly journals Amino Acid Residues That Contribute to Substrate Specificity of Class A β-Lactamase SME-1

2005 ◽  
Vol 49 (8) ◽  
pp. 3421-3427 ◽  
Author(s):  
Fahd K. Majiduddin ◽  
Timothy Palzkill
Keyword(s):  
Substrate Specificity ◽  
Active Site ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Amino Acid Residues ◽  
Class A ◽  
Study Support ◽  
Functional Mutants ◽  
Hydrolysis Of ◽  
Traditional Class

ABSTRACT Carbapenem antibiotics are used as antibiotics of last resort because they possess a broad spectrum of antimicrobial activity and are not easily hydrolyzed by β-lactamases. Recently, class A enzymes, such as the SME-1, NMC-A, and IMI-1 β-lactamases, have been identified with the capacity to hydrolyze carbapenem antibiotics. Traditional class A β-lactamases, such as TEM-1 and SHV-1, are unable to hydrolyze carbapenem antibiotics and exhibit some differences in sequence from those that are able to hydrolyze carbapenem antibiotics. The positions that differ may contribute to the unique substrate specificity of the class A carbapenemase SME-1. Codons in the SME-1 gene representing residues 104, 105, 132, 167, 237, and 241 were randomized by site-directed mutagenesis, and functional mutants were selected for the ability to hydrolyze imipenem, ampicillin, or cefotaxime. Although several positions are important for hydrolysis of β-lactam antibiotics, no single position was found to uniquely contribute to carbapenem hydrolysis. The results of this study support a model whereby the carbapenemase activity of SME-1 is due to a highly distributed set of interactions that subtly alter the structure of the active-site pocket.

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