@article {1983, title = {Structural and functional characterization of CMP-N-acetylneuraminate synthetase from Vibrio cholerae.}, journal = {Acta Crystallogr D Struct Biol}, volume = {75}, year = {2019}, month = {2019 Jun 01}, pages = {564-577}, abstract = {

Several pathogenic bacteria utilize sialic acid, including host-derived N-acetylneuraminic acid (Neu5Ac), in at least two ways: they use it as a nutrient source and as a host-evasion strategy by coating themselves with Neu5Ac. Given the significant role of sialic acid in pathogenesis and host-gut colonization by various pathogenic bacteria, including Neisseria meningitidis, Haemophilus influenzae, Pasteurella multocida and Vibrio cholerae, several enzymes of the sialic acid catabolic, biosynthetic and incorporation pathways are considered to be potential drug targets. In this work, findings on the structural and functional characterization of CMP-N-acetylneuraminate synthetase (CMAS), a key enzyme in the incorporation pathway, from Vibrio cholerae are reported. CMAS catalyzes the synthesis of CMP-sialic acid by utilizing CTP and sialic acid. Crystal structures of the apo and the CDP-bound forms of the enzyme were determined, which allowed the identification of the metal cofactor Mg in the active site interacting with CDP and the invariant Asp215 residue. While open and closed structural forms of the enzyme from eukaryotic and other bacterial species have already been characterized, a partially closed structure of V.\ cholerae CMAS (VcCMAS) observed upon CDP binding, representing an intermediate state, is reported here. The kinetic data suggest that VcCMAS is capable of activating the two most common sialic acid derivatives, Neu5Ac and Neu5Gc. Amino-acid sequence and structural comparison of the active site of VcCMAS with those of eukaryotic and other bacterial counterparts reveal a diverse hydrophobic pocket that interacts with the C5 substituents of sialic acid. Analyses of the thermodynamic signatures obtained from the binding of the nucleotide (CTP) and the product (CMP-sialic acid) to VcCMAS provide fundamental information on the energetics of the binding process.

}, keywords = {Amino Acid Sequence, Bacterial Proteins, Binding Sites, Catalytic Domain, Crystallization, Crystallography, X-Ray, Cytidine Diphosphate, Cytidine Monophosphate N-Acetylneuraminic Acid, Cytidine Triphosphate, N-Acylneuraminate Cytidylyltransferase, Protein Interaction Domains and Motifs, Protein Structure, Quaternary, Sialic Acids, Vibrio cholerae}, issn = {2059-7983}, doi = {10.1107/S2059798319006831}, author = {Bose, Sucharita and Purkait, Debayan and Joseph, Deepthi and Nayak, Vinod and Subramanian, Ramaswamy} } @article {1597, title = {Crystal structures and kinetics of N-acetylneuraminate lyase from Fusobacterium nucleatum.}, journal = {Acta Crystallogr F Struct Biol Commun}, volume = {74}, year = {2018}, month = {2018 Nov 01}, pages = {725-732}, abstract = {

N-Acetyl-D-neuraminic acid lyase (NanA) catalyzes the breakdown of sialic acid (Neu5Ac) to N-acetyl-D-mannosamine (ManNAc) and pyruvate. NanA plays a key role in Neu5Ac catabolism in many pathogenic and bacterial commensals where sialic acid is available as a carbon and nitrogen source. Several pathogens or commensals decorate their surfaces with sialic acids as a strategy to escape host innate immunity. Catabolism of sialic acid is key to a range of host-pathogen interactions. In this study, atomic resolution structures of NanA from Fusobacterium nucleatum (FnNanA) in ligand-free and ligand-bound forms are reported at 2.32 and 1.76 {\r A} resolution, respectively. F. nucleatum is a Gram-negative pathogen that causes gingival and periodontal diseases in human hosts. Like other bacterial N-acetylneuraminate lyases, FnNanA also shares the triosephosphate isomerase (TIM)-barrel fold. As observed in other homologous enzymes, FnNanA forms a tetramer. In order to characterize the structure-function relationship, the steady-state kinetic parameters of the enzyme are also reported.

}, keywords = {Bacterial Proteins, Crystallography, X-Ray, Fusobacterium nucleatum, Hydrogen Bonding, Models, Molecular, N-Acetylneuraminic Acid, Oxo-Acid-Lyases, Protein Conformation, Protein Folding, Pyruvic Acid, Schiff Bases, Sequence Alignment, Tyrosine}, issn = {2053-230X}, doi = {10.1107/S2053230X18012992}, author = {Kumar, Jay Prakash and Rao, Harshvardhan and Nayak, Vinod and Ramaswamy, S} } @article {1185, title = {Crystal structure of N-acetylmannosamine kinase from Fusobacterium nucleatum.}, journal = {Acta Crystallogr F Struct Biol Commun}, volume = {73}, year = {2017}, month = {2017 Jun 01}, pages = {356-362}, abstract = {

Sialic acids comprise a varied group of nine-carbon amino sugars that are widely distributed among mammals and higher metazoans. Some human commensals and bacterial pathogens can scavenge sialic acids from their environment and degrade them for use as a carbon and nitrogen source. The enzyme N-acetylmannosamine kinase (NanK; EC 2.7.1.60) belongs to the transcriptional repressors, uncharacterized open reading frames and sugar kinases (ROK) superfamily. NanK catalyzes the second step of the sialic acid catabolic pathway, transferring a phosphate group from adenosine 5{\textquoteright}-triphosphate to the C6 position of N-acetylmannosamine to generate N-acetylmannosamine 6-phosphate. The structure of NanK from Fusobacterium nucleatum was determined to 2.23 {\r A} resolution by X-ray crystallography. Unlike other NanK enzymes and ROK family members, F. nucleatum NanK does not have a conserved zinc-binding site. In spite of the absence of the zinc-binding site, all of the major structural features of enzymatic activity are conserved.

}, keywords = {Adenosine Triphosphate, Amino Acid Sequence, Bacterial Proteins, Binding Sites, Cloning, Molecular, Crystallography, X-Ray, Escherichia coli, Fusobacterium nucleatum, Gene Expression, Genetic Vectors, Hexosamines, Models, Molecular, Phosphotransferases (Alcohol Group Acceptor), Protein Binding, Protein Conformation, alpha-Helical, Protein Conformation, beta-Strand, Protein Interaction Domains and Motifs, Protein Multimerization, Recombinant Proteins, Sequence Alignment, Sequence Homology, Amino Acid, Substrate Specificity}, issn = {2053-230X}, doi = {10.1107/S2053230X17007439}, author = {Caing-Carlsson, Rhawnie and Goyal, Parveen and Sharma, Amit and Ghosh, Swagatha and Setty, Thanuja Gangi and North, Rachel A and Friemann, Rosmarie and Ramaswamy, S} } @article {1204, title = {Horse Liver Alcohol Dehydrogenase: Zinc Coordination and Catalysis.}, journal = {Biochemistry}, volume = {56}, year = {2017}, month = {2017 07 18}, pages = {3632-3646}, abstract = {

During catalysis by liver alcohol dehydrogenase (ADH), a water bound to the catalytic zinc is replaced by the oxygen of the substrates. The mechanism might involve a pentacoordinated zinc or a double-displacement reaction with participation by a nearby glutamate residue, as suggested by studies of human ADH3, yeast ADH1, and some other tetrameric ADHs. Zinc coordination and participation of water in the enzyme mechanism were investigated by X-ray crystallography. The apoenzyme and its complex with adenosine 5{\textquoteright}-diphosphoribose have an open protein conformation with the catalytic zinc in one position, tetracoordinated by Cys-46, His-67, Cys-174, and a water molecule. The bidentate chelators 2,2{\textquoteright}-bipyridine and 1,10-phenanthroline displace the water and form a pentacoordinated zinc. The enzyme-NADH complex has a closed conformation similar to that of ternary complexes with coenzyme and substrate analogues; the coordination of the catalytic zinc is similar to that found in the apoenzyme, except that a minor, alternative position for the catalytic zinc is \~{}1.3 {\r A} from the major position and closer to Glu-68, which could form the alternative coordination to the catalytic zinc. Complexes with NADH and N-1-methylhexylformamide or N-benzylformamide (or with NAD and fluoro alcohols) have the classical tetracoordinated zinc, and no water is bound to the zinc or the nicotinamide rings. The major forms of the enzyme in the mechanism have a tetracoordinated zinc, where the carboxylate group of Glu-68 could participate in the exchange of water and substrates on the zinc. Hydride transfer in the Michaelis complexes does not involve a nearby water.

}, keywords = {2,2{\textquoteright}-Dipyridyl, Adenosine Diphosphate Ribose, Alcohol Dehydrogenase, Animals, Catalytic Domain, Crystallography, X-Ray, Formamides, Horses, Kinetics, Liver, Models, Molecular, NAD, Phenanthrolines, Protein Binding, Protein Conformation, Water, Zinc}, issn = {1520-4995}, doi = {10.1021/acs.biochem.7b00446}, author = {Plapp, Bryce V and Savarimuthu, Baskar Raj and Ferraro, Daniel J and Rubach, Jon K and Brown, Eric N and Ramaswamy, S} } @article {1203, title = {Structural and functional studies of ferredoxin and oxygenase components of 3-nitrotoluene dioxygenase from Diaphorobacter sp. strain DS2.}, journal = {PLoS One}, volume = {12}, year = {2017}, month = {2017}, pages = {e0176398}, abstract = {

3-nitrotoluene dioxygenase (3NTDO) from Diaphorobacter sp. strain DS2 catalyses the conversion of 3-nitrotoluene (3NT) into a mixture of 3- and 4-methylcatechols with release of nitrite. We report here, X-ray crystal structures of oxygenase and ferredoxin components of 3NTDO at 2.9 {\r A} and 2.4 {\r A}, respectively. The residues responsible for nitrite release in 3NTDO were further probed by four single and two double mutations in the catalytic site of α-subunit of the dioxygenase. Modification of Val 350 to Phe, Ile 204 to Ala, and Asn258 to Val by site directed mutagenesis resulted in inactive enzymes revealing the importance of these residues in catalysis. Docking studies of meta nitrotoluene to the active site of 3NTDO suggested possible orientations of binding that favor the formation of 3-methylcatechol (3MC) over 4-methylcatechol energetically. The electron transfer pathway from ferredoxin subunit to the active site of the oxygenase subunit is also proposed.

}, keywords = {Catalytic Domain, Comamonadaceae, Crystallography, X-Ray, Ferredoxins, Molecular Docking Simulation, Mutation, Oxygenases, Substrate Specificity, Toluene}, issn = {1932-6203}, doi = {10.1371/journal.pone.0176398}, author = {Kumari, Archana and Singh, Deepak and Ramaswamy, S and Ramanathan, Gurunath} } @article {1167, title = {Blue protein with red fluorescence.}, journal = {Proc Natl Acad Sci U S A}, volume = {113}, year = {2016}, month = {2016 10 11}, pages = {11513-11518}, abstract = {

The walleye (Sander vitreus) is a golden yellow fish that inhabits the Northern American lakes. The recent sightings of the blue walleye and the correlation of its sighting to possible increased UV radiation have been proposed earlier. The underlying molecular basis of its adaptation to increased UV radiation is the presence of a protein (Sandercyanin)-ligand complex in the mucus of walleyes. Degradation of heme by UV radiation results in the formation of Biliverdin IXα (BLA), the chromophore bound to Sandercyanin. We show that Sandercyanin is a monomeric protein that forms stable homotetramers on addition of BLA to the protein. A structure of the Sandercyanin-BLA complex, purified from the fish mucus, reveals a glycosylated protein with a lipocalin fold. This protein-ligand complex absorbs light in the UV region (λ of 375 nm) and upon excitation at this wavelength emits in the red region (λ of 675 nm). Unlike all other known biliverdin-bound fluorescent proteins, the chromophore is noncovalently bound to the protein. We provide here a molecular rationale for the observed spectral properties of Sandercyanin.

}, keywords = {Biliverdine, Crystallography, X-Ray, Fluorescence, Models, Molecular, Proteins, Recombinant Proteins}, issn = {1091-6490}, doi = {10.1073/pnas.1525622113}, author = {Ghosh, Swagatha and Yu, Chi-Li and Ferraro, Daniel J and Sudha, Sai and Pal, Samir Kumar and Schaefer, Wayne F and Gibson, David T and Ramaswamy, S} }