UMLS:C0348321 - FACTA Search

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Query: UMLS:C0348321 (Haemophilus)
15,372 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Formylation of the initiator methionyl-tRNA by methionyl-tRNA formyltransferase (MTF) is an essential step in initiation of protein synthesis in eubacteria. Here, site-directed mutagenesis was used to identify active site residues of the Haemophilus influenzae MTF. Of the nine residues investigated, only Arg-41, Asn-107, His-109 and Asp-145 were important for the function of the H. influenzae MTF. Replacement of these residues with Ala resulted in a significant reduction in the efficiency of catalysis. Intrinsic fluorescence analysis indicated that this was not due to a defect in N10-formyltetrahydrofolate (fTHF) binding. The Asp-145 and Arg-41 mutations reduced the affinity of the enzyme for the initiator tRNA, whereas the Asn-107 and His-109 mutations affected catalysis but not tRNA binding. Replacement of Arg-41, His-109 and Asp-145 with functionally similar residues also affected the activity of the enzyme. The data suggest that Asn-107, His-109 and Asp-145 are catalytic residues, whereas Arg-41 is involved in tRNA recognition. In the Escherichia coli glycinamide ribonucleotide formyltransferase, which also uses fTHF as the formyl donor, Asn-106, His-108 and Asp-144 participate in the catalytic step. Together, these observations imply that this group of enzymes uses the same basic mechanism in formylating their substrates.
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PMID:Mapping the active site of the Haemophilus influenzae methionyl-tRNA formyltransferase: residues important for catalysis and tRNA binding. 1008 28

Recognition of transcription regulation sites (operators) is a hard problem in computational molecular biology. In most cases, small sample size and low degree of sequence conservation preclude the construction of reliable recognition rules. We suggest an approach to this problem based on simultaneous analysis of several related genomes. It appears that as long as a gene coding for a transcription regulator is conserved in the compared bacterial genomes, the regulation of the respective group of genes (regulons) also tends to be maintained. Thus a gene can be confidently predicted to belong to a particular regulon in case not only itself, but also its orthologs in other genomes have candidate operators in the regulatory regions. This provides for a greater sensitivity of operator identification as even relatively weak signals are likely to be functionally relevant when conserved. We use this approach to analyze the purine (PurR), arginine (ArgR) and aromatic amino acid (TrpR and TyrR) regulons of Escherichia coli and Haemophilus influenzae. Candidate binding sites in regulatory regions of the respective H.influenzae genes are identified, a new family of purine transport proteins predicted to belong to the PurR regulon is described, and probable regulation of arginine transport by ArgR is demonstrated. Differences in the regulation of some orthologous genes in E.coli and H.influenzae, in particular the apparent lack of the autoregulation of the purine repressor gene in H.influenzae, are demonstrated.
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PMID:Computer analysis of transcription regulatory patterns in completely sequenced bacterial genomes. 1039 May 42

The affinity of [(3)H]benzylpenicillin for penicillin-binding protein (PBP) 3A was reduced in 25 clinical isolates of beta-lactamase-negative ampicillin (AMP)-resistant (BLNAR) Haemophilus influenzae for which the AMP MIC was > or =1.0 microg/ml. The affinities of PBP 3B and PBP 4 were also reduced in some strains. The sequences of the ftsI gene encoding the transpeptidase domain of PBP 3A and/or PBP 3B and of the dacB gene encoding PBP 4 were determined for these strains and compared to those of AMP-susceptible Rd strains. The BLNAR strains were classified into three groups on the basis of deduced amino acid substitutions in the ftsI gene, which is thought to be involved in septal peptidoglycan synthesis. His-517, near the conserved Lys-Thr-Gly (KTG) motif, was substituted for Arg-517 in group I strains (n = 9), and Lys-526 was substituted for Asn-526 in group II strains (n = 12). In group III strains (n = 4), three residues (Met-377, Ser-385, and Leu-389), positioned near the conserved Ser-Ser-Asn (SSN) motif, were replaced with Ile, Thr, and Phe, respectively, in addition to the replacement with Lys-526. The MICs of cephem antibiotics with relatively high affinities for PBP 3A and PBP 3B were higher than those of AMP and meropenem for group III strains. The MICs of beta-lactams for H. influenzae transformants into which the ftsI gene from BLNAR strains was introduced were as high as those for the donors, and PBP 3A and PBP 3B showed decreased affinities for beta-lactams. There was no clear relationship between 7-bp deletions in the dacB gene and AMP susceptibility. Even though mutations in another gene(s) may be involved in beta-lactam resistance, these data indicate that mutations in the ftsI gene are the most important for development of resistance to beta-lactams in BLNAR strains.
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PMID:Association of amino acid substitutions in penicillin-binding protein 3 with beta-lactam resistance in beta-lactamase-negative ampicillin-resistant Haemophilus influenzae. 1135 13

The crystal structure of YecO from Haemophilus influenzae (HI0319), a protein annotated in the sequence databases as hypothetical, and that has not been assigned a function, has been determined at 2.2-A resolution. The structure reveals a fold typical of S-adenosyl-L-methionine-dependent (AdoMet) methyltransferase enzymes. Moreover, a processed cofactor, S-adenosyl-L-homocysteine (AdoHcy), is bound to the enzyme, further confirming the biochemical function of HI0319 and its sequence family members. An active site arginine, shielded from bulk solvent, interacts with an anion, possibly a chloride ion, which in turn interacts with the sulfur atom of AdoHcy. The AdoHcy and nearby protein residues delineate a small solvent-excluded substrate binding cavity of 162 A(3) in volume. The environment surrounding the cavity indicates that the substrate molecule contains a hydrophobic moiety and an anionic group. Many of the residues that define the cavity are invariant in the HI0319 sequence family but are not conserved in other methyltransferases. Therefore, the substrate specificity of YecO enzymes is unique and differs from the substrate specificity of all other methyltransferases sequenced to date. Examination of the Enzyme Commission list of methyltransferases prompted a manual inspection of 10 possible substrates using computer graphics and suggested that the ortho-substituted benzoic acids fit best in the active site.
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PMID:Crystal structure of YecO from Haemophilus influenzae (HI0319) reveals a methyltransferase fold and a bound S-adenosylhomocysteine. 1174 87

The sequences of the ftsI gene, encoding the transpeptidase domain of penicillin binding protein (PBP) 3A and/or PBP 3B, which are involved in septal peptidoglycan synthesis, were determined for 108 clinical strains of Haemophilus influenzae with reduced susceptibility to beta-lactam antibiotics with or without beta-lactamase production and were compared to those of the ampicillin-susceptible Rd strain and ampicillin-susceptible clinical isolates. The sequences have 18 different mutation patterns and were classified into two groups on the basis of amino acid substitutions deduced from the nucleotide sequences located between bp 960 and 1618 of the ftsI gene. In group I strains (n = 7), His-517 was substituted for Arg-517. In group II strains (n = 101), Lys-526 was substituted for Asn-526. In subgroup IIa (n = 5; H. influenzae ATCC 49247), the only observed substitution was Lys-526 for Asn-526; in subgroup IIb (n = 56), Val-502 was substituted for Ala-502 (n = 13), along with several other substitutions: Asn-350 for Asp-350 (n = 15), Asn-350 for Asp-350 and Glu-490 for Gly-490 (n = 14), and Asn-350 for Asp-350 and Ser-437 for Ala-437 (n = 5). In subgroup IIc (n = 25), Thr-502 was substituted for Ala-502. In subgroup IId, Val-449 was substituted for Ile-449 (n = 15). The MICs of beta-lactam antibiotics for the 108 strains were to 8 to 16 times the MICs for susceptible strains. The strains, isolated from both adults and children, were analyzed for genetic relationship by pulsed-field gel electrophoresis and by determination of ftsI sequence phylogeny. Both analyses revealed the lack of clonality and the heterogeneity of the strains, but some clusters suggest the spread and/or persistence of a limited number of strains of the same pulsotype and pattern of amino acid substitutions. Reduced susceptibility to beta-lactam, brought about by mutations of the ftsI gene, is becoming a frequent phenomenon, affecting both strains that produce beta-lactamase and those that do not. The level of resistance remains low but opens the way to greater resistance in the future.
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PMID:Diversity of beta-lactam resistance-conferring amino acid substitutions in penicillin-binding protein 3 of Haemophilus influenzae. 1206 76

Lactoferrin is a member of the lactotransferrin family of non-haem, iron-binding glycoproteins and is found at high concentrations in all human secretions, where it plays a major role in mucosal defence. In recent work, we observed that lactoferrin has proteolytic activity and attenuates the pathogenic potential of Haemophilus influenzae by cleaving and removing two putative colonization factors, namely the IgA1 protease protein and the Hap adhesin. Experiments with protease inhibitors further suggested that lactoferrin may belong to a serine protease family. In the present study we explored the mechanism of lactoferrin protease activity and discovered that mutation of either Ser259 or Lys73 results in a dramatic decrease in proteolysis. Examination of the crystal structure revealed that these two residues are located in the N-terminal lobe of the protein, adjacent to a 12-15 A cleft that separates the N-lobe and the C-lobe and that can readily accommodate large polypeptide substrates. In additional work, we found that lactoferrin cleaves IgA1 protease at an arginine-rich region defined by amino acids 1379-1386 (RRSRRSVR) and digests Hap at an arginine-rich sequence between amino acids 1016 and 1023 (VRSRRAAR). Based on our results, we conclude that lactoferrin is a serine protease capable of cleaving arginine-rich sequences. We speculate that Ser259 and Lys73 form a catalytic dyad, reminiscent of a number of bacterial serine proteases. In addition, we speculate that lactoferrin may cleave arginine-rich sequences in a variety of microbial virulence proteins, contributing to its long-recognized antimicrobial properties.
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PMID:Human milk lactoferrin is a serine protease that cleaves Haemophilus surface proteins at arginine-rich sites. 1253 64

UDP-N-acetylmuramic acid:L-alanine ligase (MurC) catalyzes the addition of the first amino acid to the cytoplasmic precursor of the bacterial cell wall peptidoglycan. The crystal structures of Haemophilus influenzae MurC in complex with its substrate UDP-N-acetylmuramic acid (UNAM) and Mg(2+) and of a fully assembled MurC complex with its product UDP-N-acetylmuramoyl-L-alanine (UMA), the nonhydrolyzable ATP analogue AMPPNP, and Mn(2+) have been determined to 1.85- and 1.7-A resolution, respectively. These structures reveal a conserved, three-domain architecture with the binding sites for UNAM and ATP formed at the domain interfaces: the N-terminal domain binds the UDP portion of UNAM, and the central and C-terminal domains form the ATP-binding site, while the C-terminal domain also positions the alanine. An active enzyme structure is thus assembled at the common domain interfaces when all three substrates are bound. The MurC active site clearly shows that the gamma-phosphate of AMPPNP is positioned between two bound metal ions, one of which also binds the reactive UNAM carboxylate, and that the alanine is oriented by interactions with the positively charged side chains of two MurC arginine residues and the negatively charged alanine carboxyl group. These results indicate that significant diversity exists in binding of the UDP moiety of the substrate by MurC and the subsequent ligases in the bacterial cell wall biosynthesis pathway and that alterations in the domain packing and tertiary structure allow the Mur ligases to bind sequentially larger UNAM peptide substrates.
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PMID:Crystal structures of active fully assembled substrate- and product-bound complexes of UDP-N-acetylmuramic acid:L-alanine ligase (MurC) from Haemophilus influenzae. 1283 90

Although Haemophilus somnus causes septicemia and vasculitis in cattle, relatively little is known about how H. somnus affects endothelial cells in vitro. We previously reported that H. somnus lipooligosaccharide (LOS)-induced activation of caspases-3, -8 and -9, and apoptosis of bovine pulmonary artery endothelial cells (BPAEC) in vitro. Previous reports indicate that the generation of reactive oxygen species (ROS) or reactive nitrogen intermediates (RNI) can contribute to the induction of apoptosis. In the present study, we sought to determine whether ROS and RNI are involved in LOS-mediated apoptosis of BPAEC. We found that H. somnus LOS induced the generation of ROS in BPAEC, which was blocked by pretreatment with membrane permeable ROS scavengers, such as dimethylsulfoxide (DMSO) and allopurinol (AP). Addition of DMSO or AP significantly reduced H. somnus LOS-mediated caspase-3 activation. Addition of membrane impermeable ROS scavengers (e.g. catalase and superoxide dismutase), failed to block LOS-mediated caspase-3 activation, suggesting a role for intracellular generation of ROS in LOS-induced apoptosis of BPAEC. Addition of N(G)-nitro-L-arginine methyl ester (L-NAME) or aminoguanidine, which are selective inhibitors of nitric oxide synthase, blocked NO release and significantly reduced caspase-3 activation in LOS treated BPAEC. These data suggest H. somnus LOS triggers endogenous ROS and RNI production by endothelial cells, which contributes to apoptosis.
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PMID:Reactive oxygen and nitrogen intermediates contribute to Haemophilus somnus lipooligosaccharide-mediated apoptosis of bovine endothelial cells. 1474 Nov 39

The reversible dephosphorylation of beta-aspartyl phosphate to L-aspartate-beta-semialdehyde (ASA) in the aspartate biosynthetic pathway is catalyzed by aspartate-beta-semialdehyde dehydrogenase (ASADH). The product of this reaction is a key intermediate in the biosynthesis of diaminopimelic acid, an integral component of bacterial cell walls and a metabolic precursor of lysine and also a precursor in the biosynthesis of threonine, isoleucine and methionine. The structures of selected Haemophilus influenzae ASADH mutants were determined in order to evaluate the residues that are proposed to interact with the substrates ASA or phosphate. The substrate Km values are not altered by replacement of either an active-site arginine (Arg270) with a lysine or a putative phosphate-binding group (Lys246) with an arginine. However, the interaction of phosphate with the enzyme is adversely affected by replacement of Arg103 with lysine and is significantly altered when a neutral leucine is substituted at this position. A conservative Glu243 to aspartate mutant does not alter either ASA or phosphate binding, but instead results in an eightfold increase in the Km for the coenzyme NADP. Each of the mutations is shown to cause specific subtle active-site structural alterations and each of these changes results in decreases in catalytic efficiency ranging from significant (approximately 3% native activity) to substantial (<0.1% native activity).
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PMID:The role of substrate-binding groups in the mechanism of aspartate-beta-semialdehyde dehydrogenase. 1527 61

Extracytoplasmic solute receptors (ESRs) are important components of solute uptake systems in bacteria, having been studied extensively as parts of ATP binding cassette transporters. Herein we report the first crystal structure of an ESR protein from a functionally characterized electrochemical ion gradient dependent secondary transporter. This protein, SiaP, forms part of a tripartite ATP-independent periplasmic transporter specific for sialic acid in Haemophilus influenzae. Surprisingly, the structure reveals an overall topology similar to ATP binding cassette ESR proteins, which is not apparent from the sequence, demonstrating that primary and secondary transporters can share a common structural component. The structure of SiaP in the presence of the sialic acid analogue 2,3-didehydro-2-deoxy-N-acetylneuraminic acid reveals the ligand bound in a deep cavity with its carboxylate group forming a salt bridge with a highly conserved Arg residue. Sialic acid binding, which obeys simple bimolecular association kinetics as determined by stopped-flow fluorescence spectroscopy, is accompanied by domain closure about a hinge region and the kinking of an alpha-helix hinge component. The structure provides insight into the evolution, mechanism, and substrate specificity of ESR-dependent secondary transporters that are widespread in prokaryotes.
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PMID:Conservation of structure and mechanism in primary and secondary transporters exemplified by SiaP, a sialic acid binding virulence factor from Haemophilus influenzae. 1670 22

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