Thirty cases of bronchial asthma associated with exposure to pet hamsters.

BACKGROUND: The identification, isolation, and elimination of allergen(s) causing bronchial asthma are the most efficient form of treatment. The pet industry has diversified recently, increasing the risk of exposure of pet owners to many unknown antigens. We clinically studied the characteristics of asthma associated with exposure to pet hamsters. METHODS: The study group comprised 30 adults in whom the onset, recurrence, or exacerbation of asthma was triggered by contact with pet hamsters. Clinical characteristics such as sex, age, period required for symptom onset, species of hamster, treatment and disease course, smoking status, and hamster-specific IgE antibodies in serum were studied. RESULTS: The male: female ratio of the study group was 1:1.3, and mean age was 37.7 years. Patients with no previous history of asthma initially presented with cough, progressing to episodes of asthma. Asthmatic symptoms were associated with hamster contact and ranged in severity from mild to severe. Three patients required hospital admission for treatment. The mean period from the start of hamster exposure to the onset of asthmatic episodes was 15.7 months. Dwarf hamsters were responsible for most cases. The CAP-RAST score for hamster-specific IgE antibodies was 1 to 4 in 22 patients and 0 in 8 patients. Eight patients with a score of 1 or higher for hamster-specific IgE antibodies had a CAP-RAST score of 0 for mite antigen. In these patients, terminating hamster contact resulted in a rapid improvement in symptoms, with no need for further treatment. Twenty-three of the 30 subjects (76.7%) were smokers. CONCLUSION: Exposure to pet hamsters is an important risk factor for the onset, recurrence, or exacerbation of asthma. Smoking may also increase the risk of asthmatic symptoms in patients exposed to hamsters.

Clinical evaluation of response to long-term treatment with Pranlukast in patients with bronchial asthma.

BACKGROUND: Short-term treatment with pranlukast, a leukotriene receptor antagonist, has shown to be effective for the management of asthma. The effectiveness and safety of long-term treatment with pranlukast remains to be established. OBJECTIVES: The aim of this study was to determine the effects of pranlukast on morning peak expiratory flow rates (PEFRs), the diurnal variation of these values, and disease severity. METHODS: Fifteen men with bronchial asthma were studied for 5 years. During the first year, the subjects were treated with a bronchodilator; some also received inhaled and oral corticosteroids. During the next 4 years, the subjects received pranlukast in addition. RESULTS: Mean PEFR increased after the start of treatment with pranlukast. The increase in PEFR occurred later in subjects with more severe disease. Diurnal variation of PEFR was unchanged, but subsequently decreased. The condition of all subjects improved, but the greatest improvement was obtained in patients with mild to moderate asthma. CONCLUSIONS: Long-term treatment with pranlukast is effective for the management of bronchial asthma, particularly in patients with mild to moderate disease. Our results suggest that the effectiveness of antiasthmatic drugs should be evaluated over a period of years, rather than on a short-term basis.

Crystallization and preliminary X-ray study of OXA-1, a class D beta-lactamase.

The Escherichia coli OXA-1 oxacillinase, a beta-lactamase which provides resistance to beta-lactam antibiotics (penicillins and cephalosporins), has been crystallized. A member of the class D family of serine beta-lactamases, OXA-1 is especially active against the penicillins oxacillin and cloxacillin and is now found in 10% of E. coli clinical isolates. Crystals grown from PEG 8000 at pH 7.5 diffract to 1.5 A resolution at 100 K and have space group P1 (Z = 2), with unit-cell parameters a = 36.0, b = 51.6, c = 72.9 A, alpha = 70.2, beta = 84.1, gamma = 81.5 degrees.

Characterization of an extended-spectrum class C beta-lactamase of Citrobacter freundii.

Citrobacter freundii GC3 is a clinical isolate which showed moderate resistance to oxyimino beta-lactams such as ceftazidime and aztreonam. This drug resistance was due to an extended-spectrum class C beta-lactamase encoded by chromosomal gene(s). The GC3 beta-lactamase showed high amino acid sequence homology to a known C. freundii beta-lactamase, i.e., 346 of 361 amino acids were identical with those of C. freundii GN346 beta-lactamase (Tsukamoto, K. et al, Eur. J. Biochem. 188, 15-22, 1990). Asp198 was the only dissimilar amino acid found in the omega loop region, known as the hot spot for extended-spectrum resistance in class C beta-lactamases (Haruta, S. et al, Microbiol. Immunol. 42, 165-169, 1998). However, Asp198 was eliminated as a cause of the extended-spectrum resistance by the substitution of Asn for Asp198. Subsequent investigation suggested that the moderate resistance to oxyimino beta-lactams is attributable to the replacement of amino acids on the enzyme's surface area, far from the active-site. Some or all of the replacements are assumed to delicately modify the active-site configuration. The GC3 beta-lactamase is the first example of an extended-spectrum class C beta-lactamase in which mutations are independent of the omega loop.

Inhibition of class C beta-lactamases: structure of a reaction intermediate with a cephem sulfone.

The crystallographic structure of the Enterobacter cloacae GC1 extended-spectrum class C beta-lactamase, inhibited by a new 7-alkylidenecephalosporin sulfone, has been determined by X-ray diffraction at 100 K to a resolution of 1.6 A. The crystal structure was solved by molecular replacement using the unliganded structure [Crichlow et al. (1999) Biochemistry 38, 10256-10261] and refined to a crystallographic R-factor equal to 0.183 (R(free) 0.208). Cryoquenching of the reaction of the sulfone with the enzyme produced an intermediate that is covalently bound via Ser64. After acylation of the beta-lactam ring, the dihydrothiazine dioxide ring opened with departure of the sulfinate. Nucleophilic attack of a side chain pyridine nitrogen atom on the C6 atom of the resultant imine yielded a bicyclic aromatic system which helps to stabilize the acyl enzyme to hydrolysis. A structural assist to this resonance stabilization is the positioning of the anionic sulfinate group between the probable catalytic base (Tyr150) and the acyl ester bond so as to block the approach of a potentially deacylating water molecule. Comparison of the liganded and unliganded protein structures showed that a major movement (up to 7 A) and refolding of part of the Omega-loop (215-224) accompanies the binding of the inhibitor. This conformational flexibility in the Omega-loop may form the basis of an extended-spectrum activity of class C beta-lactamases against modern cephalosporins.

Inhibition of the SHV-1 beta-lactamase by sulfones: crystallographic observation of two reaction intermediates with tazobactam.

Two species resulting from the reaction of the SHV-1 class A beta-lactamase with the sulfone inhibitor tazobactam have been trapped at 100 K and mapped by X-ray crystallography at 2.0 A resolution. An acyclic form of tazobactam is covalently bonded to the catalytic Ser70 side chain, and a second species, a five-atom vinyl carboxylic acid fragment of tazobactam, is bonded to Ser130. It is proposed that the electron density map of the crystal is a composite picture of two complexes, each with only a single bound species. It is estimated that the two complexes exist in the crystal in approximately equal populations. Results are discussed in relation to the mechanism-based inhibition of class A beta-lactamases by the similar inhibitors sulbactam and clavulanic acid.

Functional analysis of the active site of a metallo-beta-lactamase proliferating in Japan.

An R-plasmid-mediated metallo-beta-lactamase was found in Klebsiella pneumoniae DK4 isolated in Japan in 1991. The nucleotide sequence of its structural gene revealed that the beta-lactamase termed DK4 was identical to the IMP-1 metallo-beta-lactamase which was mediated by a chromosomal gene of Serratia marcescens TN9106 isolated in Japan in 1991 (E. Osano et al., Antimicrob. Agents Chemother. 38:71-78, 1994). The dose effect of DK4 beta-lactamase production on the resistance levels indicated a significant contribution of the enzyme to bacterial resistance to all the beta-lactams except monobactams. The enzymatic characteristics of the DK4 beta-lactamase and its kinetic parameters for nine beta-lactams were examined. The DK4 beta-lactamase was confirmed to contain 2 mol of zinc per mol of enzyme protein. The apoenzyme that lacked the two zincs was structurally unstable, and the activities of only 30% of the apoenzyme molecules could be restored by the addition of 1 mM zinc sulfate. The substitution of five conserved histidines (His28, His86, His88, His149, His210) and a cysteine (Cys168) for an alanine indicated that His86, His88, and His149 served as ligands to one of the zincs and that Cys168 played a role as a ligand to the second zinc. Both zinc molecules contribute to the enzymatic process. Mutant enzymes that lack only one of these retained some activity. Additionally, a conserved aspartic acid at position 90 was replaced by asparagine. This mutant enzyme showed an approximately 1,000 times lower k(cat) value for cephalothin than that of the wild-type enzyme but retained the two zincs even after dialysis against zinc-free buffer. The observed effect of pH on the activity suggested that Asp90 functions as a general base in the enzymatic process.

Structure of the extended-spectrum class C beta-lactamase of Enterobacter cloacae GC1, a natural mutant with a tandem tripeptide insertion.

A class C beta-lactamase from a clinical isolate of Enterobacter cloacae strain GC1 with improved hydrolytic activity for oxyimino beta-lactam antibiotics has been analyzed by X-ray crystallography to 1.8 A resolution. Relative to the wild-type P99 beta-lactamase, this natural mutant contains a highly unique tandem repeat Ala211-Val212-Arg213 [Nugaka et al. (1995) J. Biol. Chem. 270, 5729-5735]. The 39.4 kDa chromosomal beta-lactamase crystallizes from poly(ethylene glycol) 8000 in potassium phosphate in space group P2(1)2(1)2 with cell dimensions a = 78.0 A, b = 69.5 A, and c = 63.1 A. The crystal structure was solved by the molecular replacement method, and the model has been refined to an R-factor of 0.20 for all nonzero data from 8 to 1.8 A. Deviations of model bonds and angles from ideal values are 0.008 A and 1.4 degrees, respectively. Overlay of alpha-carbon atoms in the GC1 and P99 beta-lactamases results in an rms deviation of 0.6 A. Largest deviations occur in a loop containing Gln120 and in the Omega loop region (200-218) where the three residues 213-215 are disordered. Possibly as a result of this disorder, the width of the opening to the substrate binding cavity, as measured from the 318-324 beta-strand to two loops containing Gln120 and Tyr150 on the other side, is 0.6-1.4 A wider than in P99. It is suggested that conformational flexibility in the expanded Omega loop, and its influence on adjacent protein structure, may facilitate hydrolysis of oxyimino beta-lactams by making the acyl intermediate more open to attack by water. Nevertheless, backbone atoms in core catalytic site residues Ser64, Lys67, Tyr150, Asn152, Lys318, and Ser321 deviate only 0.4 A (rmsd) from atoms in P99. A rotation of a potential catalytic base, Tyr150, relative to P99 at pH 8, is consistent with the requirement for a lower than normal pK(a) for this residue.

Structure of the SHV-1 beta-lactamase.

The X-ray crystallographic structure of the SHV-1 beta-lactamase has been established. The enzyme crystallizes from poly(ethylene glycol) at pH 7 in space group P212121 with cell dimensions a = 49.6 A, b = 55.6 A, and c = 87.0 A. The structure was solved by the molecular replacement method, and the model has been refined to an R-factor of 0.18 for all data in the range 8.0-1.98 A resolution. Deviations of model bonds and angles from ideal values are 0.018 A and 1.8 degrees, respectively. Overlay of all 263 alpha-carbon atoms in the SHV-1 and TEM-1 beta-lactamases results in an rms deviation of 1.4 A. Largest deviations occur in the H10 helix (residues 218-224) and in the loops between strands in the beta-sheet. All atoms in residues 70, 73, 130, 132, 166, and 234 in the catalytic site of SHV-1 deviate only 0.23 A (rms) from atoms in TEM-1. However, the width of the substrate binding cavity in SHV-1, as measured from the 104-105 and 130-132 loops on one side to the 235-238 beta-strand on the other side, is 0.7-1.2 A wider than in TEM-1. A structural analysis of the highly different affinity of SHV-1 and TEM-1 for the beta-lactamase inhibitory protein BLIP focuses on interactions involving Asp/Glu104.

Effect of an amino acid insertion into the omega loop region of a class C beta-lactamase on its substrate specificity.

The extended-substrate specificity of Enterobacter cloacae GC1 beta-lactamase is entirely due to a three amino acid insertion after position 207. To clarify the reason for the extended-substrate specificity, Ala, Ala-Ala, Ala-Ala-Ala, and Ala-Ala-Ala-Ala were inserted after position 207 on the basis of the class C beta-lactamase from E. cloacae P99, respectively. The kcat and Km values of all the mutant enzymes for cephalothin, benzylpenicillin and ampicillin were almost the same as those of the wild-type enzyme, except for those of P99-210-4A which were decreased 4-15-fold. On the other hand, the kcat and Km values for oxyimino beta-lactams such as cefuroxime, ceftazidime, and aztreonam increased with increasing numbers of inserted alanines. The kcat values of the mutant enzymes for cefroxime increased 140-7400-fold compared with that of the wild-type. The Km values also increased with almost the same magnitude, resulting in about the same kcat/Km values as that of the wild-type. On progressive inhibition analysis of aztreonam of the mutant enzymes, two kinds of inactive acyl-enzyme with distinct stabilities were observed, and the proportion of the less stable inactive enzyme increased with increasing numbers of inserted alanines. This suggests that the extension of the substrate specificity is due to instability of the acyl-intermediate caused by an increased deacylation rate in the reaction process.

Resistance to oxyimino beta-lactams due to a mutation of chromosomal beta-lactamase in Citrobacter freundii.

The duplicative mutation of an Ala-Val-Arg sequence at positions 208 to 210 in the loop structure of Enterobacter cloacae class C beta-lactamase caused substrate specificity extension to oxyimino beta-lactam antibiotics and this chromosomal mutation provided bacterial cells with high resistance to the beta-lactams (M. Nukaga et al, 1995, J. Biol. Chem. 270, 5729-5735). In order to confirm the universality of this phenomenon among other class C beta-lactamases, the duplicative mutation was applied to a class C beta-lactamase of Citrobacter freundii, which has 74% homology to the E. cloacae beta-lactamase amino acid sequence. The counterpart sequence to the Ala-Val-Arg of the E. cloacae enzyme in C. freundii beta-lactamase was identified to be Pro-Val-His. A Pro-Val-His sequence was inserted just after the native Pro-Val-His sequence at positions 208 to 210 in the C. freundii beta-lactamase. The resulting mutant of C. freundii beta-lactamase obtained a striking characteristic that we expected, showing substrate specificity extension to oxyimino beta-lactams. Nearly the same result was obtained with the insertion of an Ala-Val-Arg sequence after the native Pro-Val-His sequence. These results indicate that structural modification of this locus commonly induces modification of the substrate specificity to unfavorable substrates for many chromosomal class C beta-lactamases produced by gram-negative bacteria.

Molecular evolution of a class C beta-lactamase extending its substrate specificity.

Enterobacter cloacae GC1, a clinical strain isolated in 1992 in Japan, was found to produce a chromosomal class C beta-lactamase with extended substrate specificity to oxyimino beta-lactam antibiotics, significantly differing from the known E. cloacae beta-lactamases such as the P99 beta-lactamase. The 1560 nucleotides including the GC1 beta-lactamase gene were sequenced, and the amino acid sequence of the mature enzyme comprising 364 amino acids was deduced. A comparison of the amino acid sequence with those of known E. cloacae beta-lactamases revealed the duplication of three amino acids at positions 208-213, i.e. Ala-Val-Arg-Ala-Val-Arg. This duplication was attributed to a tandem duplication of a 9-nucleotide sequence. The chimeric beta-lactamases produced by the chimeric genes from the GC1 and P99 beta-lactamase genes indicated that the extended substrate specificity is entirely attributed to the 3-amino acid insertion. Two mutant beta-lactamases were prepared from P99 beta-lactamase by site-directed mutagenesis, i.e. an Ala-Ala-Ala sequence was inserted before or after the native Ala-Val-Arg at positions 208-210. These mutant enzymes revealed that the Ala-Val-Arg located from positions 211 to 213 in the GC1 beta-lactamase are the newly inserted residues, and this phenomenon is independent of the characteristics of the amino acids inserted.

Replacement of serine 237 in class A beta-lactamase of Proteus vulgaris modifies its unique substrate specificity.

The chromosomal beta-lactamase gene of Proteus vulgaris K1 was cloned and sequenced. The gene comprises 813 nucleotides and codes for the mature enzyme of 29,655 Da, comprising 271 amino acids. The K1 beta-lactamase showed 30-70% similarity, in the overall amino acid sequence, to class A beta-lactamases of Gram-negative bacteria. However, the K1 beta-lactamase differs from most class A enzymes in having a unique substrate specificity as a cephalosporinase, its spectrum extending to even oxyiminocephalosporins. To clarify the relationship between its unique substrate specificity and specific amino acid residues, alignment of the amino acid sequence of the K1 beta-lactamase with those of class A beta-lactamases was performed, and Ala104 and Ser237 were found to be candidates. Ala104 and Ser237 were replaced with glutamic acid and alanine, respectively, which are commonly found in other class A beta-lactamases. The substitution at position 104 had no effect on the enzyme activity or the substrate specificity. The amino acid replacement at position 237, however, reduced the kcat/Km value for an oxyiminocephalosporin (cefuroxime) to 17% of that in the case of the wild-type enzyme, whereas the mutant enzyme showed a higher kcat/Km value for benzylpenicillin, 3 times, than that of the wild-type enzyme. These results indicated that Ser237 is one of the residues responsible for the unique substrate specificity of the P. vulgaris beta-lactamase.

Interaction of oxyimino beta-lactams with a class C beta-lactamase and a mutant with a spectrum extended to beta-lactams.

The class C beta-lactamase of Citrobacter freundii GN346 is a typical cephalosporinase comprising 361 amino acids, and substitution of the glutamic acid at position 219 in the enzyme by lysine was previously shown to broaden its substrate spectrum to oxyimino beta-lactams (K. Tsukamoto, R. Ohno, and T. Sawai, J. Bacteriol. 172:4348-4351, 1990). To clarify this spectrum extension from the kinetic point of view, the interactions of cefuroxime, ceftazidime, and aztreonam with the wild-type and mutant enzymes were analyzed. In addition to aztreonam, known as a progressive inhibitor of class C beta-lactamases, cefuroxime and ceftazidime were found to act as progressive inhibitors of the wild-type enzyme. On the other hand, only aztreonam showed weak progressive inhibition of the mutant enzyme. On the basis of kinetic parameters, a minimum scheme for interaction of the oxyimino beta-lactams with the wild-type enzyme was proposed, and the rate-limiting step of the hydrolysis of unfavorable substrates was indicated to be conversion of the stable acyl-enzyme intermediate to the unstable intermediate. In aztreonam hydrolysis by the mutant enzyme, the reaction rate at the rate-limiting step was 2,000 times that of the wild-type enzyme. These results indicate that the mutation at position 219 disturbs the stabilization of the stable intermediate.

A survey of a functional amino acid of class C beta-lactamase corresponding to Glu166 of class A beta-lactamases.

The class C beta-lactamase of Citrobacter freundii GN346 is a typical cephalosporinase comprising 361 amino acids. The aspartic acid at position 217 and glutamic acid at position 219 in this beta-lactamase were, respectively, previously shown not to be the counterpart of Glu166 (ABL166) in class A beta-lactamases, even though sequence alignment of class A and C enzymes strongly suggested this possibility [(1990) FEBS Lett. 264, 211-214; (1990) J. Bacteriol. 172, 4348-4351]. We tried again to assign candidates for the counterpart of Glu166 through sequence alignment based on other criteria, the glutamic acids at positions 195 and 205 in the class C beta-lactamase being selected. To investigate this possibility, these two glutamic acids were changed to glutamine, lysine or alanine, respectively. All the mutant enzymes showed more than 50% of the activity of the wild-type enzyme, indicating that the possibility was ruled out. These results strongly suggested the possibility that the class C beta-lactamase lacks a functional acidic residue corresponding to Glu166 in class A enzymes.

The effect of amino acid substitution at position 219 of Citrobacter freundii cephalosporinase on extension of its substrate spectrum.

The cephalosporinase of Citrobacter freundii GN346 is a class-C beta-lactamase comprising 361 amino acids. The substitution of the glutamic acid at position 219 in the enzyme by lysine was previously shown to broaden its substrate specificity to unfavorable substrates such as oxyimino cephalosporins [Tsukamoto, K., Ohno, R. & Sawai, T. (1990) J. Bacteriol. 172, 4348-4351]. To investigate the cause of this phenomenon, Glu219 was changed to glutamine, cysteine or tryptophan. All the resultant enzymes showed higher cefuroxime-hydrolytic activities than the wild type, the order of increasing cefuroxime-hydrolytic activity being as follows: Trp greater than Lys greater than Cys greater than Gln greater than Glu. The rate of hydrolysis of cefuroxime by the Trp219 enzyme was approximately 3 x 10(4) times that of the wild-type enzyme. The order of increasing cefuroxime hydrolysis was approximately proportional to the molecular volume of the amino acid substituted and independent of the ionic character of the amino acids. The cysteine residue at position 219 in the Cys219 enzyme allowed its complete reaction with an SH-blocking reagent, 4-chloromercuriphenylsulfonic acid. The modified enzyme with the bulkier residue showed a 45% higher cefuroxime-hydrolytic activity than the untreated enzyme. These results suggested that extension of the substrate spectrum may be attributed to alteration in the configuration of the enzyme around position 219.