Biochemical and Structural studies of the type I tagatose bisphosphate aldolases
Freichels, Régine ; ; Delmarcelle, Michaël et al
Poster (2013, February 26)Detailed reference viewed: 25 (2 ULg)
Structure of the E. coli amidase AmiC and its activation by the LytM cofactor NlpD
Kerff, Frédéric ; Rocaboy, Mathieu ; Herman, Raphaël et al
Poster (2012, June 25)Detailed reference viewed: 18 (4 ULg)
Novel fragments of clavulanate observed in the structure of the class A b-lactamase from Bacillus licheniformis BS3
; Mercuri, Paola ; Herman, Raphaël et al
in Journal of Antimicrobial Chemotherapy (2012), 67(10), 2379-2387Detailed reference viewed: 12 (4 ULg)
Unexpected tricovalent binding mode of boronic acids within the active site of a penicillin binding protein.
Zervosen, Astrid ; Herman, Raphaël ; Kerff, Frédéric et al
in Journal of the American Chemical Society (2011)
Boronic acids bearing appropriate side chains are good inhibitors of serine amidohydrolases. The boron usually adopts a tetrahedral conformation, bound to the nucleophilic serine of the active site and ... [more ▼]
Boronic acids bearing appropriate side chains are good inhibitors of serine amidohydrolases. The boron usually adopts a tetrahedral conformation, bound to the nucleophilic serine of the active site and mimicking the transition state of the enzymatic reaction. We have solved the structures of complexes of a penicillin-binding protein, the DD-peptidase from Actinomadura sp. R39, with four amidomethylboronic acids (2,6 dimethoxybenzamidomethylboronic acid, phenylacetamidomethylboronic acid, 2-chlorobenzamidomethylboronic acid, and 2-nitrobenzamidomethylboronic acid) and the pinacol ester derived from phenylacetamidomethylboronic acid. We found that, in each case, the boron forms a tricovalent adduct with Ogamma of Ser49, Ser298, and the terminal amine group of Lys410, three key residues involved in the catalytic mechanism of penicillin-binding proteins. This represents the first tricovalent enzyme-inhibitor adducts observed by crystallography. In two of the five R39-boronate structures, the boronic acid is found as a tricovalent adduct in two monomers of the asymmetric unit and as a monocovalent adduct with the active serine in the two remaining monomers of the asymmetric unit. Formation of the tricovalent complex from a classical monocovalent complex may involve rotation around the Ser49 Calpha-Cbeta bond to place the boron in a position to interact with Ser298 and Lys410, and a twisting of the side chain amide such that its carbonyl oxygen is able to hydrogen bond to the oxyanion hole NH of Thr413. Biphasic kinetics were observed in three of the five cases and details of the reaction between R39 and 2,6-dimethoxybenzamidomethylboronic acid were studied. Observation of biphasic kinetics was not, however, thought to be correlated to formation of tricovalent complexes, assuming that the latter do form in solution. Based on the crystallographic and kinetic results, a reaction scheme for this unexpected inhibition by boronic acids is proposed. [less ▲]Detailed reference viewed: 37 (10 ULg)
Distant and new mutations in CTX-M-1 beta-lactamase affect cefotaxime hydrolysis.
; Kerff, Frédéric ; et al
in Antimicrobial Agents and Chemotherapy (2011), 55(9), 4361-8
The CTX-M beta-lactamases are an increasingly prevalent group of extended-spectrum beta-lactamases (ESBL). Point mutations in CTX-M beta-lactamases are considered critical for enhanced hydrolysis of ... [more ▼]
The CTX-M beta-lactamases are an increasingly prevalent group of extended-spectrum beta-lactamases (ESBL). Point mutations in CTX-M beta-lactamases are considered critical for enhanced hydrolysis of cefotaxime. In order to clarify the structural determinants of the activity against cefotaxime in CTX-M beta-lactamases, screening for random mutations was carried out to search for decreased activity against cefotaxime, with the CTX-M-1 gene as a model. Thirteen single mutants with a considerable reduction in cefotaxime MICs were selected for biochemical and stability studies. The 13 mutated genes of the CTX-M-1 beta-lactamase were expressed, and the proteins were purified for kinetic studies against cephalothin and cefotaxime (as the main antibiotics). Some of the positions, such as Val103Asp, Asn104Asp, Asn106Lys, and Pro107Ser, are located in the (103)VNYN(106) loop, which had been described as important in cefotaxime hydrolysis, although this has not been experimentally confirmed. There are four mutations located close to catalytic residues-Thr71Ile, Met135Ile, Arg164His, and Asn244Asp-that may affect the positioning of these residues. We show here that some distant mutations, such as Ala219Val, are critical for cefotaxime hydrolysis and highlight the role of this loop at the top of the active site. Other distant substitutions, such as Val80Ala, Arg191, Ala247Ser, and Val260Leu, are in hydrophobic cores and may affect the dynamics and flexibility of the enzyme. We describe here, in conclusion, new residues involved in cefotaxime hydrolysis in CTX-M beta-lactamases, five of which are in positions distant from the catalytic center. [less ▲]Detailed reference viewed: 22 (1 ULg)
Three factors that modulate the activity of class D β-lactamases and interfere with the post-translational carboxylation of Lys 70
Vercheval, Lionel ; Di Paolo, Alexandre ; et al
in Biochemical Journal (2010), 432(3), 495-504
Lys-70 carboxylation in the active site of class D β lactamases is essential for their activity. Structural, kinetic and affinity studies show that this post-translational modification can be affected by ... [more ▼]
Lys-70 carboxylation in the active site of class D β lactamases is essential for their activity. Structural, kinetic and affinity studies show that this post-translational modification can be affected by the presence of a poor substrate such as moxalactam but also by the V117T substitution. Val-117 is a strictly conserved hydrophobic residue located in the active site. In addition, inhibition of class D β lactamases by chloride ions is due to a competition between the side chain carboxylate of the modified Lys 70 and chloride ions. Determination of the individual kinetic constants shows that the deacylation of the acyl-enzyme is the rate limiting step for the wild type OXA 10 β lactamase. [less ▲]Detailed reference viewed: 73 (22 ULg)
A Tripeptide Deletion in the Class C beta-Lactamase FOX-4 Enzyme Impairs Cefoxitin Hydrolysis and Slightly Increases Susceptibility to beta-Lactamase Inhibitors
; ; Kerff, Frédéric et al
in Journal of Antimicrobial Chemotherapy (2010), 65(6), 1187-94
OBJECTIVES: A natural variant of the AmpC enzyme from Escherichia coli HKY28 with a tripeptide deletion (Gly-286/Ser-287/Asp-288) was recently described. The isolate produced an inhibitor-sensitive AmpC ... [more ▼]
OBJECTIVES: A natural variant of the AmpC enzyme from Escherichia coli HKY28 with a tripeptide deletion (Gly-286/Ser-287/Asp-288) was recently described. The isolate produced an inhibitor-sensitive AmpC beta-lactamase variant that also conferred higher than usual levels of resistance to ceftazidime in the E. coli host. To demonstrate whether this is true in other class C beta-lactamase enzymes, we deleted the equivalent tripeptide in the FOX-4 plasmid-mediated class C beta-lactamase. METHODS: By site-directed mutagenesis, we deleted the tripeptide Gly-306/Asn-307/Ser-308 of FOX-4, thus generating FOX-4(DeltaGNS). The enzymes (FOX-4 wild-type and DeltaGNS) were purified and kinetic parameters (kcat, Km, kcat/Km) as well as IC50 values of several beta-lactams were assessed. Modelling studies were also performed. RESULTS: FOX-4(DeltaGNS) did not increase the catalytic efficiency towards ceftazidime, although it conferred a slight increase in the susceptibility to beta-lactamase inhibitors. There was also a noteworthy decrease in the cefoxitin MIC with the FOX-4(DeltaGNS) mutant (from 512 to 16 mg/L) as well as a 10-fold decrease in kcat/Km towards imipenem, which revealed specific structural features. CONCLUSIONS: Although deletions in the R2-loop are able to extend the substrate spectrum of class C enzymes, the present results do not confirm this hypothesis in FOX-4. The FOX-4 R2 site would already be wide enough to accommodate antibiotic molecules, and thus any amino acid replacement or deletion at this location would not affect the hydrolytic efficiency towards beta-lactams and would have a less drastic effect on the susceptibility to beta-lactamase inhibitors. [less ▲]Detailed reference viewed: 48 (7 ULg)
Specific Structural Features of the N-Acetylmuramoyl-l-Alanine Amidase AmiD from Escherichia coli and Mechanistic Implications for Enzymes of This Family.
Kerff, Frédéric ; ; Mercier, Frédéric et al
in Journal of Molecular Biology (2010), 397
AmiD is the fifth identified N-acetylmuramoyl-l-alanine zinc amidase of Escherichia coli. This periplasmic lipoprotein is anchored in the outer membrane and has a broad specificity. AmiD is capable of ... [more ▼]
AmiD is the fifth identified N-acetylmuramoyl-l-alanine zinc amidase of Escherichia coli. This periplasmic lipoprotein is anchored in the outer membrane and has a broad specificity. AmiD is capable of cleaving the intact peptidoglycan (PG) as well as soluble fragments containing N-acetylmuramic acid regardless of the presence of an anhydro form or not, unlike the four other amidases, AmiA, AmiB, AmiC, and AmpD, which have some specificity. AmiD function is, however, not clearly established but it could be part of the enzymatic machinery involved in the PG turnover in E. coli. We solved three structures of the E. coli zinc amidase AmiD devoid of its lipidic anchorage: the holoenzyme, the apoenzyme in complex with the substrate anhydro-N-acetylmuramic-acid-l-Ala-gamma-d-Glu-l-Lys, and the holoenzyme in complex with the l-Ala-gamma-d-Glu-l-Lys peptide, the product of the hydrolysis of this substrate by AmiD. The AmiD structure shows a relatively flexible N-terminal extension that allows an easy reach of the PG by the enzyme inserted into the outer membrane. The C-terminal domain provides a potential extended geometrical complementarity to the substrate. AmiD shares a common fold with AmpD, the bacteriophage T7 lysozyme, and the PG recognition proteins, which are receptor proteins involved in the innate immune responses of a wide range of organisms. Analysis of the different structures reveals the similarity between the catalytic mechanism of zinc amidases of the AmiD family and the thermolysin-related zinc peptidases. [less ▲]Detailed reference viewed: 73 (16 ULg)
Simple di- and trivanillates exhibit cytostatic properties toward cancer cells resistant to pro-apoptotic stimuli.
; ; Kerff, Frédéric et al
in Bioorganic & Medicinal Chemistry (2010), 18(11), 3823-33
A series of 33 novel divanillates and trivanillates were synthesized and found to possess promising cytostatic rather than cytotoxic properties. Several compounds under study decreased by >50% the ... [more ▼]
A series of 33 novel divanillates and trivanillates were synthesized and found to possess promising cytostatic rather than cytotoxic properties. Several compounds under study decreased by >50% the activity of Aurora A, B, and C, and WEE1 kinase activity at concentrations <10% of their IC(50) growth inhibitory ones, accounting, at least partly, for their cytostatic effects in cancer cells and to a lesser extent in normal cells. Compounds 6b and 13c represent interesting starting points for the development of cytostatic agents to combat cancers, which are naturally resistant to pro-apoptotic stimuli, including metastatic malignancies. [less ▲]Detailed reference viewed: 60 (1 ULg)
Crystal structure of a complex between the Actinomadura R39 DD-peptidase and a peptidoglycan-mimetic boronate inhibitor: interpretation of a transition state analogue in terms of catalytic mechanism.
; Rocaboy, Mathieu ; Kerff, Frédéric et al
in Biochemistry (2010), 49(30), 6411-9
The Actinomadura R39 DD-peptidase is a bacterial low molecular weight class C penicillin-binding protein. It has previously been shown to catalyze hydrolysis and aminolysis of small D-alanyl-D-alanine ... [more ▼]
The Actinomadura R39 DD-peptidase is a bacterial low molecular weight class C penicillin-binding protein. It has previously been shown to catalyze hydrolysis and aminolysis of small D-alanyl-D-alanine terminating peptides, especially those with a side chain that mimics the amino terminus of the stem peptide precursor to the bacterial cell wall. This paper describes the synthesis of (D-alpha-aminopimelylamino)-D-1-ethylboronic acid, designed to be a peptidoglycan-mimetic transition state analogue inhibitor of the R39 DD-peptidase. The boronate was found to be a potent inhibitor of the peptidase with a K(i) value of 32 +/- 6 nM. Since it binds some 30 times more strongly than the analogous peptide substrate, the boronate may well be a transition state analogue. A crystal structure of the inhibitory complex shows the boronate covalently bound to the nucleophilic active site Ser 49. The aminopimelyl side chain is bound into the site previously identified as specific for this moiety. One boronate oxygen is held in the oxyanion hole; the other, occupying the leaving group site of acylation or the nucleophile site of deacylation, appears to be hydrogen-bonded to the hydroxyl group of Ser 298. The Ser 49 oxygen appears to be hydrogen bonded to Lys 52. If it is assumed that this structure does resemble a high-energy tetrahedral intermediate in catalysis, it seems likely that Ser 298 participates as part of a proton transfer chain initiated by Lys 52 or Lys 410 as the primary proton donor/acceptor. The structure, therefore, supports a particular class of mechanism that employs this proton transfer device. [less ▲]Detailed reference viewed: 24 (3 ULg)
Role of changes in the L3 loop of the active site in the evolution of enzymatic activity of VIM-type metallo-beta-lactamases.
; ; Kerff, Frédéric et al
in Journal of Antimicrobial Chemotherapy (2010), 65(9), 1950-4
OBJECTIVES: The new metallo-beta-lactamase VIM-13 has been recently characterized. In comparison with the VIM-1 enzyme, VIM-13 showed 19 amino acid differences, 2 of which were located in the active site ... [more ▼]
OBJECTIVES: The new metallo-beta-lactamase VIM-13 has been recently characterized. In comparison with the VIM-1 enzyme, VIM-13 showed 19 amino acid differences, 2 of which were located in the active site centre. The main objective of the present study was to assess whether differences between VIM-1 and VIM-13 beta-lactamases in the active site, at His224Leu and Ser228Arg, are necessary and sufficient to explain the microbiological and biochemical differences between the two enzymes. METHODS: Single mutants VIM-13 (Leu224His) and VIM-13 (Arg228Ser) and double mutant VIM-13 (Leu224His, Arg228Ser) were created by site-directed mutagenesis with the bla(VIM-13) gene as template. VIM-1, VIM-13 and VIM-13 (Leu224His, Arg228Ser) were purified by affinity chromatography, and kinetic parameters for these enzymes were obtained with ceftazidime, cefepime and ampicillin. RESULTS: Ceftazidime and cefepime MICs (mg/L) for Escherichia coli TG1 expressing VIM-1, VIM-13, VIM-13 (Leu224His), VIM-13 (Arg228Ser) and VIM-13 (Leu224His, Arg228Ser) were >256 and 64, 6 and 4, 8 and 1, >256 and 8, and >256 and 48, respectively. VIM-1, VIM-13 and VIM-13 (Leu224His, Arg228Ser) revealed k(cat)/K(m) values (M(-1)s(-1)) for ceftazidime of 3.7 E(4), 1.9 E(4) and 10 E(4), respectively, and revealed k(cat)/K(m) values for cefepime of 3.5 E(5), 3 E(4) and 1.5 E(5), respectively. CONCLUSIONS: Overall, the results showed that the two residues located in the L3 loop are sufficient to confer the substrate specificity of each enzyme, thus highlighting the importance of the L3 loop of the active site in the evolution of VIM-type metallo-beta-lactamases. [less ▲]Detailed reference viewed: 9 (1 ULg)
Critical role of tryptophan 154 for the activity and stability of class D beta-lactamases.
; Vercheval, Lionel ; Bouillenne, Fabrice et al
in Biochemistry (2009), 48(47), 11252-63
The catalytic efficiency of the class D beta-lactamase OXA-10 depends critically on an unusual carboxylated lysine as the general base residue for both the enzyme acylation and deacylation steps of ... [more ▼]
The catalytic efficiency of the class D beta-lactamase OXA-10 depends critically on an unusual carboxylated lysine as the general base residue for both the enzyme acylation and deacylation steps of catalysis. Evidence is presented that the interaction between the indole group of Trp154 and the carboxylated lysine is essential for the stability of the posttranslationally modified Lys70. Substitution of Trp154 by Gly, Ala, or Phe yielded noncarboxylated enzymes which displayed poor catalytic efficiencies and reduced stability when compared to the wild-type OXA-10. The W154H mutant was partially carboxylated. In addition, the maximum values of k(cat) and k(cat)/K(M) were shifted toward pH 7, indicating that the carboxylation state of Lys70 is dependent on the protonation level of the histidine. A comparison of the three-dimensional structures of the different proteins also indicated that the Trp154 mutations did not modify the overall structures of OXA-10 but induced an increased flexibility of the Omega-loop in the active site. Finally, the deacylation-impaired W154A mutant was used to determine the structure of the acyl-enzyme complex with benzylpenicillin. These results indicate a role of the Lys70 carboxylation during the deacylation step and emphasize the importance of Trp154 for the ideal positioning of active site residues leading to an optimum activity. [less ▲]Detailed reference viewed: 42 (10 ULg)
Structural basis of the inhibition of class A beta-lactamases and penicillin-binding proteins by 6-beta-iodopenicillanate
Sauvage, Eric ; Zervosen, Astrid ; Dive, Georges et al
in Journal of the American Chemical Society (2009), 131(42), 15262-15269
6-Beta-halogenopenicillanates are powerful, irreversible inhibitors of various beta-lactamases and penicillin-binding proteins. Upon acylation of these enzymes, the inhibitors are thought to undergo a ... [more ▼]
6-Beta-halogenopenicillanates are powerful, irreversible inhibitors of various beta-lactamases and penicillin-binding proteins. Upon acylation of these enzymes, the inhibitors are thought to undergo a structural rearrangement associated with the departure of the iodide and formation of a dihydrothiazine ring, but, to date, no structural evidence has proven this. 6-Beta-iodopenicillanic acid (BIP) is shown here to be an active antibiotic against various bacterial strains and an effective inhibitor of the class A beta-lactamase of Bacillus subtilis BS3 (BS3) and the D,D-peptidase of Actinomadura R39 (R39). Crystals of BS3 and of R39 were soaked with a solution of BIP and their structures solved at 1.65 and 2.2 A, respectively. The beta-lactam and the thiazolidine rings of BIP are indeed found to be fused into a dihydrothiazine ring that can adopt two stable conformations at these active sites. The rearranged BIP is observed in one conformation in the BS3 active site and in two monomers of the asymmetric unit of R39, and is observed in the other conformation in the other two monomers of the asymmetric unit of R39. The BS3 structure reveals a new mode of carboxylate interaction with a class A beta-lactamase active site that should be of interest in future inhibitor design. [less ▲]Detailed reference viewed: 67 (27 ULg)
Specific structural features of the N-acetylmuramyl-L-Alanine amidase AmiD from E.coli and general implication for the mechanism of action of this family of enzyme
Poster (2008, August)Detailed reference viewed: 3 (0 ULg)
The Penicillin-Binding Proteins: Structure and Role in Peptidoglycan Biosynthesis
Sauvage, Eric ; Kerff, Frédéric ; Terrak, Mohammed et al
in FEMS Microbiology Reviews (2008), 32(2), 234-58
Penicillin-binding proteins (PBPs) have been scrutinized for over 40 years. Recent structural information on PBPs together with the ongoing long-term biochemical experimental investigations, and results ... [more ▼]
Penicillin-binding proteins (PBPs) have been scrutinized for over 40 years. Recent structural information on PBPs together with the ongoing long-term biochemical experimental investigations, and results from more recent techniques such as protein localization by green fluorescent protein-fusion immunofluorescence or double-hybrid assay, have brought our understanding of the last stages of the peptidoglycan biosynthesis to an outstanding level that allows a broad outlook on the properties of these enzymes. Details are emerging regarding the interaction between the peptidoglycan-synthesizing PBPs and the peptidoglycan, their mesh net-like product that surrounds and protects bacteria. This review focuses on the detailed structure of PBPs and their implication in peptidoglycan synthesis, maturation and recycling. An overview of the content in PBPs of some bacteria is provided with an emphasis on comparing the biochemical properties of homologous PBPs (orthologues) belonging to different bacteria. [less ▲]Detailed reference viewed: 56 (17 ULg)
Crystal structure of a cold-adapted class C beta-lactamase.
; ; Kerff, Frédéric et al
in FEBS Journal (2008), 275(8), 1687-97
In this study, the crystal structure of a class C beta-lactamase from a psychrophilic organism, Pseudomonas fluorescens, has been refined to 2.2 A resolution. It is one of the few solved crystal ... [more ▼]
In this study, the crystal structure of a class C beta-lactamase from a psychrophilic organism, Pseudomonas fluorescens, has been refined to 2.2 A resolution. It is one of the few solved crystal structures of psychrophilic proteins. The structure was compared with those of homologous mesophilic enzymes and of another, modeled, psychrophilic protein. The elucidation of the 3D structure of this enzyme provides additional insights into the features involved in cold adaptation. Structure comparison of the psychrophilic and mesophilic beta-lactamases shows that electrostatics seems to play a major role in low-temperature adaptation, with a lower total number of ionic interactions for cold enzymes. The psychrophilic enzymes are also characterized by a decreased number of hydrogen bonds, a lower content of prolines, and a lower percentage of arginines in comparison with lysines. All these features make the structure more flexible so that the enzyme can behave as an efficient catalyst at low temperatures. [less ▲]Detailed reference viewed: 21 (1 ULg)
Crystal structure and activity of Bacillus subtilis YoaJ (EXLX1), a bacterial expansin that promotes root colonization.
Kerff, Frédéric ; Amoroso, Ana Maria ; Herman, Raphaël et al
in Proceedings of the National Academy of Sciences of the United States of America (2008), 105(44), 16876-81
We solved the crystal structure of a secreted protein, EXLX1, encoded by the yoaJ gene of Bacillus subtilis. Its structure is remarkably similar to that of plant beta-expansins (group 1 grass pollen ... [more ▼]
We solved the crystal structure of a secreted protein, EXLX1, encoded by the yoaJ gene of Bacillus subtilis. Its structure is remarkably similar to that of plant beta-expansins (group 1 grass pollen allergens), consisting of 2 tightly packed domains (D1, D2) with a potential polysaccharide-binding surface spanning the 2 domains. Domain D1 has a double-psi beta-barrel fold with partial conservation of the catalytic site found in family 45 glycosyl hydrolases and in the MltA family of lytic transglycosylases. Domain D2 has an Ig-like fold similar to group 2/3 grass pollen allergens, with structural features similar to a type A carbohydrate-binding domain. EXLX1 bound to plant cell walls, cellulose, and peptidoglycan, but it lacked lytic activity against a variety of plant cell wall polysaccharides and peptidoglycan. EXLX1 promoted plant cell wall extension similar to, but 10 times weaker than, plant beta-expansins, which synergistically enhanced EXLX1 activity. Deletion of the gene encoding EXLX1 did not affect growth or peptidoglycan composition of B. subtilis in liquid medium, but slowed lysis upon osmotic shock and greatly reduced the ability of the bacterium to colonize maize roots. The presence of EXLX1 homologs in a small but diverse set of plant pathogens further supports a role in plant-bacterial interactions. Because plant expansins have proved difficult to express in active form in heterologous systems, the discovery of a bacterial homolog opens the door for detailed structural studies of expansin function. [less ▲]Detailed reference viewed: 99 (7 ULg)
Mutational analysis of the zinc- and substrate-binding sites in the CphA metallo-beta-lactamase from Aeromonas hydrophila.
Bebrone, Carine ; ; Kerff, Frédéric et al
in Biochemical Journal (2008), 414(1), 151-9
The subclass B2 CphA (Carbapenemase hydrolysing Aeromonas) beta-lactamase from Aeromonas hydrophila is a Zn(2+)-containing enzyme that specifically hydrolyses carbapenems. In an effort to evaluate ... [more ▼]
The subclass B2 CphA (Carbapenemase hydrolysing Aeromonas) beta-lactamase from Aeromonas hydrophila is a Zn(2+)-containing enzyme that specifically hydrolyses carbapenems. In an effort to evaluate residues potentially involved in metal binding and/or catalysis (His(118), Asp(120), His(196) and His(263)) and in substrate specificity (Val(67), Thr(157), Lys(224) and Lys(226)), site-directed mutants of CphA were generated and characterized. Our results confirm that the first zinc ion is in interaction with Asp(120) and His(263), and thus is located in the 'cysteine' zinc-binding site. His(118) and His(196) residues seem to be interacting with the second zinc ion, as their replacement by alanine residues has a negative effect on the affinity for this second metal ion. Val(67) plays a significant role in the binding of biapenem and benzylpenicillin. The properties of a mutant with a five residue (LFKHV) insertion just after Val(67) also reveals the importance of this region for substrate binding. This latter mutant has a higher affinity for the second zinc ion than wild-type CphA. The T157A mutant exhibits a significantly modified activity spectrum. Analysis of the K224Q and N116H/N220G/K224Q mutants suggests a significant role for Lys(224) in the binding of substrate. Lys(226) is not essential for the binding and hydrolysis of substrates. Thus the present paper helps to elucidate the position of the second zinc ion, which was controversial, and to identify residues important for substrate binding. [less ▲]Detailed reference viewed: 32 (7 ULg)