RESUMEN
Protein stability is an essential property for biological function. In contrast to the vast knowledge on protein stability in vitro, little is known about the factors governing in-cell stability. Here we show that the metallo-ß-lactamase (MBL) New Delhi MBL-1 (NDM-1) is a kinetically unstable protein on metal restriction that has evolved by acquiring different biochemical traits that optimize its in-cell stability. The nonmetalated (apo) NDM-1 is degraded by the periplasmic protease Prc that recognizes its partially unstructured C-terminal domain. Zn(II) binding renders the protein refractory to degradation by quenching the flexibility of this region. Membrane anchoring makes apo-NDM-1 less accessible to Prc and protects it from DegP, a cellular protease degrading misfolded, nonmetalated NDM-1 precursors. NDM variants accumulate substitutions at the C terminus that quench its flexibility, enhancing their kinetic stability and bypassing proteolysis. These observations link MBL-mediated resistance with the essential periplasmic metabolism, highlighting the importance of the cellular protein homeostasis.
Asunto(s)
Péptido Hidrolasas , beta-Lactamasas , beta-Lactamasas/genética , beta-Lactamasas/metabolismo , Estabilidad Proteica , Proteolisis , Péptido Hidrolasas/metabolismo , Antibacterianos , Pruebas de Sensibilidad MicrobianaRESUMEN
L1 is a dizinc subclass B3 metallo-ß-lactamase (MBL) that hydrolyzes most ß-lactam antibiotics and is a key resistance determinant in the Gram-negative pathogen Stenotrophomonas maltophilia, an important cause of nosocomial infections in immunocompromised patients. L1 is not usefully inhibited by MBL inhibitors in clinical trials, underlying the need for further studies on L1 structure and mechanism. We describe kinetic studies and crystal structures of L1 in complex with hydrolyzed ß-lactams from the penam (mecillinam), cephem (cefoxitin/cefmetazole), and carbapenem (tebipenem, doripenem, and panipenem) classes. Despite differences in their structures, all the ß-lactam-derived products hydrogen bond to Tyr33, Ser221, and Ser225 and are stabilized by interactions with a conserved hydrophobic pocket. The carbapenem products were modeled as Δ1-imines, with (2S)-stereochemistry. Their binding mode is determined by the presence of a 1ß-methyl substituent: the Zn-bridging hydroxide either interacts with the C-6 hydroxyethyl group (1ß-hydrogen-containing carbapenems) or is displaced by the C-6 carboxylate (1ß-methyl-containing carbapenems). Unexpectedly, the mecillinam product is a rearranged N-formyl amide rather than penicilloic acid, with the N-formyl oxygen interacting with the Zn-bridging hydroxide. NMR studies imply mecillinam rearrangement can occur nonenzymatically in solution. Cephem-derived imine products are bound with (3R)-stereochemistry and retain their 3' leaving groups, likely representing stable endpoints, rather than intermediates, in MBL-catalyzed hydrolysis. Our structures show preferential complex formation by carbapenem- and cephem-derived species protonated on the equivalent (ß) faces and so identify interactions that stabilize diverse hydrolyzed antibiotics. These results may be exploited in developing antibiotics, and ß-lactamase inhibitors, that form long-lasting complexes with dizinc MBLs.
Asunto(s)
Antibacterianos , Inhibidores de beta-Lactamasas , beta-Lactamas , Humanos , Antibacterianos/farmacología , Inhibidores de beta-Lactamasas/farmacología , beta-Lactamasas/química , beta-Lactamas/química , beta-Lactamas/metabolismo , beta-Lactamas/farmacología , Carbapenémicos/metabolismo , Cristalografía , Cinética , Stenotrophomonas maltophilia/efectos de los fármacos , Infecciones por Bacterias Gramnegativas/tratamiento farmacológicoRESUMEN
Taniborbactam (TAN) is a novel broad-spectrum ß-lactamase inhibitor with significant activity against subclass B1 metallo-ß-lactamases (MBLs). Here, we showed that TAN exhibited an overall excellent activity against B1 MBLs including most NDM- and VIM-like as well as SPM-1, GIM-1, and DIM-1 enzymes, but not against SIM-1. Noteworthy, VIM-1-like enzymes (particularly VIM-83) were less inhibited by TAN than VIM-2-like. Like NDM-9, NDM-30 (also differing from NDM-1 by a single amino acid substitution) was resistant to TAN.
Asunto(s)
Ácidos Borínicos , beta-Lactamasas , beta-Lactamasas/química , Inhibidores de beta-Lactamasas/farmacología , Ácidos Borínicos/farmacología , Ácidos Carboxílicos/farmacología , Antibacterianos/farmacología , Pruebas de Sensibilidad MicrobianaRESUMEN
The design of inhibitors against metallo-ß-lactamases (MBLs), the largest family of carbapenemases, has been a strategic goal in designing novel antimicrobial therapies. In this regard, the development of bicyclic boronates, such as taniborbactam (TAN) and xeruborbactam, is a major achievement that may help in overcoming the threat of MBL-producing and carbapenem-resistant Gram-negative pathogens. Of concern, a recent report has shown that New Delhi MBL-9 (NDM-9) escapes the inhibitory action of TAN by a single amino acid substitution with respect to New Delhi MBL-1 (NDM-1), the most widely disseminated MBL. Here, we report a docking and computational analysis that identifies that "escape variants" against TAN can arise by disruption of the electrostatic interaction of negative charges in the active site loops of MBLs with the N-(2-aminoethyl)cyclohexylamine side chain of TAN. These changes result in non-productive binding modes of TAN that preclude reaction with the MBLs, a phenomenon that is not restricted to NDM-9. This analysis demonstrates that single amino acid substitutions in non-essential residues in MBL loops can unexpectedly elicit resistance to TAN.
Asunto(s)
Antibacterianos , Ácidos Borínicos , Ácidos Carboxílicos , Antibacterianos/farmacología , Inhibidores de beta-Lactamasas/farmacología , beta-Lactamasas/metabolismo , Ácidos Borínicos/farmacología , Resistencia betalactámica , Pruebas de Sensibilidad MicrobianaRESUMEN
Imipenemase (IMP) metallo-ß-lactamases (MBLs) hydrolyze almost all available ß-lactams including carbapenems and are not inhibited by any commercially available ß-lactamase inhibitor. Tebipenem (TP) pivoxil is the first orally available carbapenem and possesses a unique bicyclic azetidine thiazole moiety located at the R2 position. TP has potent in vitro activity against Enterobacterales producing extended-spectrum and/or AmpC ß-lactamases. Thus far, the activity of TP against IMP-producing strains is understudied. To address this knowledge gap, we explored the structure activity relationships of IMP MBLs by investigating whether IMP-6, IMP-10, IMP-25, and IMP-78 [MBLs with expanded hydrolytic activity against meropenem (MEM)] would demonstrate enhanced activity against TP. Most of the Escherichia coli DH10B strains expressing IMP-1 variants displayed a ≥twofold MIC difference between TP and MEM, while those expressing VIM or NDM variants demonstrated comparable MICs. Catalytic efficiency (kcat/KM) values for the TP hydrolysis by IMP-1, IMP-6, IMP-10, IMP-25, and IMP-78 were significantly lower than those obtained for MEM. Molecular dynamic simulations reveal that V67F and S262G substitutions (found in IMP-78) reposition active site loop 3, ASL-3, to better accommodate the bicyclic azetidine thiazole side chain, allowing microbiological/catalytic activity to approach that of comparison MBLs used in this study. These findings suggest that modifying the R2 side chain of carbapenems can significantly impact hydrolytic stability. Furthermore, changes in conformational dynamics due to single amino acid substitutions should be used to inform drug design of novel carbapenems.
Asunto(s)
Antibacterianos , Azetidinas , Carbapenémicos , Dominio Catalítico , Escherichia coli , Pruebas de Sensibilidad Microbiana , Tiazoles , beta-Lactamasas , beta-Lactamasas/genética , beta-Lactamasas/metabolismo , Carbapenémicos/farmacología , Antibacterianos/farmacología , Tiazoles/farmacología , Tiazoles/química , Azetidinas/farmacología , Azetidinas/química , Escherichia coli/efectos de los fármacos , Escherichia coli/genética , Simulación de Dinámica Molecular , Meropenem/farmacología , Meropenem/química , Relación Estructura-ActividadRESUMEN
Taniborbactam (TAN; VNRX-5133) is a novel bicyclic boronic acid ß-lactamase inhibitor (BLI) being developed in combination with cefepime (FEP). TAN inhibits both serine and some metallo-ß-lactamases. Previously, the substitution R228L in VIM-24 was shown to increase activity against oxyimino-cephalosporins like FEP and ceftazidime (CAZ). We hypothesized that substitutions at K224, the homologous position in NDM-1, could impact FEP/TAN resistance. To evaluate this, a library of codon-optimized NDM K224X clones for minimum inhibitory concentration (MIC) measurements was constructed; steady-state kinetics and molecular docking simulations were next performed. Surprisingly, our investigation revealed that the addition of TAN restored FEP susceptibility only for NDM-1, as the MICs for the other 19 K224X variants remained comparable to those of FEP alone. Moreover, compared to NDM-1, all K224X variants displayed significantly lower MICs for imipenem, tebipenem, and cefiderocol (32-, 133-, and 33-fold lower, respectively). In contrast, susceptibility to CAZ was mostly unaffected. Kinetic assays with the K224I variant, the only variant with hydrolytic activity to FEP comparable to NDM-1, confirmed that the inhibitory capacity of TAN was modestly compromised (IC50 0.01 µM vs 0.14 µM for NDM-1). Lastly, structural modeling and docking simulations of TAN in NDM-1 and in the K224I variant revealed that the hydrogen bond between TAN's carboxylate with K224 is essential for the productive binding of TAN to the NDM-1 active site. In addition to the report of NDM-9 (E149K) as FEP/TAN resistant, this study demonstrates the fundamental role of single amino acid substitutions in the inhibition of NDM-1 by TAN.
Asunto(s)
Antibacterianos , Ácidos Borínicos , Antibacterianos/farmacología , Simulación del Acoplamiento Molecular , Ácidos Carboxílicos/farmacología , Ácidos Borínicos/farmacología , Ceftazidima , Inhibidores de beta-Lactamasas/farmacología , beta-Lactamasas/metabolismo , Pruebas de Sensibilidad MicrobianaRESUMEN
Understanding the evolution of metallo-ß-lactamases (MBLs) is fundamental to deciphering the mechanistic basis of resistance to carbapenems in pathogenic and opportunistic bacteria. Presently, these MBL-producing pathogens are linked to high rates of morbidity and mortality worldwide. However, the study of the biochemical and biophysical features of MBLs in vitro provides an incomplete picture of their evolutionary potential, since this limited and artificial environment disregards the physiological context where evolution and selection take place. Herein, we describe recent efforts aimed to address the evolutionary traits acquired by different clinical variants of MBLs in conditions mimicking their native environment (the bacterial periplasm) and considering whether they are soluble or membrane-bound proteins. This includes addressing the metal content of MBLs within the cell under zinc starvation conditions and the context provided by different bacterial hosts that result in particular resistance phenotypes. Our analysis highlights recent progress bridging the gap between in vitro and in-cell studies.
Asunto(s)
Bacterias , Periplasma , beta-Lactamasas , Antibacterianos/química , Bacterias/enzimología , Bacterias/metabolismo , Carbapenémicos , Periplasma/enzimología , Periplasma/metabolismo , beta-Lactamasas/químicaRESUMEN
Protein evolution depends on the adaptation of these molecules to different functional challenges. This occurs by tuning their biochemical, biophysical, and structural traits through the accumulation of mutations. While the role of protein dynamics in biochemistry is well recognized, there are limited examples providing experimental evidence of the optimization of protein dynamics during evolution. Here we report an NMR study of four variants of the CTX-M ß-lactamases, in which the interplay of two mutations outside the active site enhances the activity against a cephalosporin substrate, ceftazidime. The crystal structures of these enzymes do not account for this activity enhancement. By using NMR, here we show that the combination of these two mutations increases the backbone dynamics in a slow timescale and the exposure to the solvent of an otherwise buried ß-sheet. The two mutations located in this ß-sheet trigger conformational changes in loops located at the opposite side of the active site. We postulate that the most active variant explores alternative conformations that enable binding of the more challenging substrate ceftazidime. The impact of the mutations in the dynamics is context-dependent, in line with the epistatic effect observed in the catalytic activity of the different variants. These results reveal the existence of a dynamic network in CTX-M ß-lactamases that has been exploited in evolution to provide a net gain-of-function, highlighting the role of alternative conformations in protein evolution.
Asunto(s)
Ceftazidima , Escherichia coli , Antibacterianos/farmacología , Ceftazidima/química , Ceftazidima/farmacología , Cefalosporinas/farmacología , Escherichia coli/genética , Solventes/farmacología , beta-Lactamasas/metabolismoRESUMEN
Antimicrobial resistance is one of the major problems in current practical medicine. The spread of genes coding for resistance determinants among bacteria challenges the use of approved antibiotics, narrowing the options for treatment. Resistance to carbapenems, last resort antibiotics, is a major concern. Metallo-ß-lactamases (MBLs) hydrolyze carbapenems, penicillins, and cephalosporins, becoming central to this problem. These enzymes diverge with respect to serine-ß-lactamases by exhibiting a different fold, active site, and catalytic features. Elucidating their catalytic mechanism has been a big challenge in the field that has limited the development of useful inhibitors. This review covers exhaustively the details of the active-site chemistries, the diversity of MBL alleles, the catalytic mechanism against different substrates, and how this information has helped developing inhibitors. We also discuss here different aspects critical to understand the success of MBLs in conferring resistance: the molecular determinants of their dissemination, their cell physiology, from the biogenesis to the processing involved in the transit to the periplasm, and the uptake of the Zn(II) ions upon metal starvation conditions, such as those encountered during an infection. In this regard, the chemical, biochemical and microbiological aspects provide an integrative view of the current knowledge of MBLs.
Asunto(s)
Resistencia a Múltiples Medicamentos , Evolución Molecular , Inhibidores de beta-Lactamasas/química , Inhibidores de beta-Lactamasas/farmacología , beta-Lactamasas/química , beta-Lactamasas/metabolismo , Animales , Humanos , Inhibidores de beta-Lactamasas/síntesis química , beta-Lactamasas/genéticaRESUMEN
We present herein the "vermellogens", a new class of pH-responsive viologen analogues, which replace the direct linking between para-substituted pyridinium moieties within those by a hydrazone functional group. A series of such compounds have been efficiently synthesized in aqueous media by hydrazone exchange reactions, displaying a marked pH-responsivity. Furthermore, the parent N,N'-dimethylated "vermellogen": the "red thread", an analogue of the herbicide paraquat and used herein as a representative model of the series, showed anion-recognition abilities, non-reversible electrochemical behavior, and non-toxicity of the modified bis-pyridinium core. The host-guest chemistry for the "red thread" with the CB[7,8] macrocyclic receptors has been extensively studied experimentally and by dispersion corrected density functional theory methods, showing a parallel behavior to that previously described for the herbicide but, crucially, swapping the well-known redox reactive capabilities of the viologen-based inclusion complexes by acid-base supramolecular responsiveness.
Asunto(s)
Herbicidas , Viológenos , Paraquat/toxicidad , Aniones , Concentración de Iones de Hidrógeno , HidrazonasRESUMEN
Outer membrane vesicles (OMVs) act as carriers of bacterial products such as plasmids and resistance determinants, including metallo-ß-lactamases. The lipidated, membrane-anchored metallo-ß-lactamase NDM-1 can be detected in Gram-negative OMVs. The soluble domain of NDM-1 also forms electrostatic interactions with the membrane. Here, we show that these interactions promote its packaging into OMVs produced by Escherichia coli. We report that favorable electrostatic protein-membrane interactions are also at work in the soluble enzyme IMP-1 while being absent in VIM-2. These interactions correlate with an enhanced incorporation of IMP-1 compared to VIM-2 into OMVs. Disruption of these interactions in NDM-1 and IMP-1 impairs their inclusion into vesicles, confirming their role in defining the protein cargo in OMVs. These results also indicate that packaging of metallo-ß-lactamases into vesicles in their active form is a common phenomenon that involves cargo selection based on specific molecular interactions.
Asunto(s)
Escherichia coli , beta-Lactamasas , Escherichia coli/genética , Plásmidos/genética , beta-Lactamasas/genéticaRESUMEN
Mitochondrial cytochrome c oxidase (COX) is the primary site of cellular oxygen consumption and is essential for aerobic energy generation in the form of ATP. Human COX is a copper-heme A hetero-multimeric complex formed by 3 catalytic core subunits encoded in the mitochondrial DNA and 11 subunits encoded in the nuclear genome. Investigations over the last 50 years have progressively shed light into the sophistication surrounding COX biogenesis and the regulation of this process, disclosing multiple assembly factors, several redox-regulated processes leading to metal co-factor insertion, regulatory mechanisms to couple synthesis of COX subunits to COX assembly, and the incorporation of COX into respiratory supercomplexes. Here, we will critically summarize recent progress and controversies in several key aspects of COX biogenesis: linear versus modular assembly, the coupling of mitochondrial translation to COX assembly and COX assembly into respiratory supercomplexes.
Asunto(s)
Complejo IV de Transporte de Electrones/metabolismo , Mitocondrias/metabolismo , Biogénesis de Organelos , HumanosRESUMEN
A 4-year surveillance of carbapenem-resistant Acinetobacter spp. isolates in Argentina identified 40 strains carrying blaNDM-1 Genome sequencing revealed that most were Acinetobacter baumannii, whereas seven represented other Acinetobacter spp. The A. baumannii genomes were closely related, suggesting recent spread. blaNDM-1 was located in the chromosome of A. baumannii strains and on a plasmid in non-A. baumannii strains. A resistance gene island carrying blaPER-7 and other resistance determinants was found on a plasmid in some A. baumannii strains.
Asunto(s)
Acinetobacter baumannii/efectos de los fármacos , Acinetobacter baumannii/genética , Antibacterianos/farmacología , Carbapenémicos/farmacología , beta-Lactamasas/genética , Infecciones por Acinetobacter/tratamiento farmacológico , Infecciones por Acinetobacter/microbiología , Acinetobacter baumannii/aislamiento & purificación , Argentina , Genoma Bacteriano/genética , Humanos , Pruebas de Sensibilidad Microbiana , Plásmidos/genéticaRESUMEN
Unlike for classes A and B, a standardized amino acid numbering scheme has not been proposed for the class C (AmpC) ß-lactamases, which complicates communication in the field. Here, we propose a scheme developed through a collaborative approach that considers both sequence and structure, preserves traditional numbering of catalytically important residues (Ser64, Lys67, Tyr150, and Lys315), is adaptable to new variants or enzymes yet to be discovered and includes a variation for genetic and epidemiological applications.
Asunto(s)
Proteínas Bacterianas/clasificación , Bacterias Gramnegativas/genética , Bacterias Grampositivas/genética , Mutación , Terminología como Asunto , Resistencia betalactámica/genética , beta-Lactamasas/clasificación , Secuencia de Aminoácidos , Antibacterianos/química , Antibacterianos/farmacología , Proteínas Bacterianas/antagonistas & inhibidores , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Expresión Génica , Bacterias Gramnegativas/efectos de los fármacos , Bacterias Gramnegativas/enzimología , Bacterias Grampositivas/efectos de los fármacos , Bacterias Grampositivas/enzimología , Cooperación Internacional , Estructura Secundaria de Proteína , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Inhibidores de beta-Lactamasas/química , Inhibidores de beta-Lactamasas/farmacología , beta-Lactamasas/genética , beta-Lactamasas/metabolismo , beta-Lactamas/química , beta-Lactamas/farmacologíaRESUMEN
CuA is a binuclear copper site acting as electron entry port in terminal heme-copper oxidases. In the oxidized form, CuA is a mixed valence pair whose electronic structure can be described using a potential energy surface with two minima, σu* and πu, that are variably populated at room temperature. We report that mutations in the first and second coordination spheres of the binuclear metallocofactor can be combined in an additive manner to tune the energy gap and, thus, the relative populations of the two lowest-lying states. A series of designed mutants span σu*/πu energy gaps ranging from 900 to 13 cm-1. The smallest gap corresponds to a variant with an effectively degenerate ground state. All engineered sites preserve the mixed-valence character of this metal center and the electron transfer functionality. An increase of the Cu-Cu distance less than 0.06 Å modifies the σu*/πu energy gap by almost 2 orders of magnitude, with longer distances eliciting a larger population of the πu state. This scenario offers a stark contrast to synthetic systems, as model compounds require a lengthening of 0.5 Å in the Cu-Cu distance to stabilize the πu state. These findings show that the tight control of the protein environment allows drastic perturbations in the electronic structure of CuA sites with minor geometric changes.
Asunto(s)
Proteínas Bacterianas/química , Complejos de Coordinación/química , Cobre/química , Grupo Citocromo b/química , Complejo IV de Transporte de Electrones/química , Secuencia de Aminoácidos , Sustitución de Aminoácidos , Proteínas Bacterianas/genética , Grupo Citocromo b/genética , Complejo IV de Transporte de Electrones/genética , Electrones , Estructura Molecular , Ingeniería de Proteínas , Subunidades de Proteína/química , Alineación de Secuencia , Termodinámica , Thermus thermophilus/enzimologíaRESUMEN
PmoD, a recently discovered protein from methane-oxidizing bacteria, forms a homodimer with a dicopper CuA center at the dimer interface. Although the optical and electron paramagnetic resonance (EPR) spectroscopic signatures of the PmoD CuA bear similarities to those of canonical CuA sites, there are also some puzzling differences. Here we have characterized the rapid formation (seconds) and slow decay (hours) of this homodimeric CuA site to two mononuclear Cu2+ sites, as well as its electronic and geometric structure, using stopped-flow optical and advanced paramagnetic resonance spectroscopies. PmoD CuA formation occurs rapidly and involves a short-lived intermediate with a λmax of 360 nm. Unlike other CuA sites, the PmoD CuA is unstable, decaying to two type 2 Cu2+ centers. Surprisingly, NMR data indicate that the PmoD CuA has a pure σu* ground state rather than the typical equilibrium between σu* and πu of all other CuA proteins. EPR, ENDOR, ESEEM, and HYSCORE data indicate the presence of two histidine and two cysteine ligands coordinating the CuA core in a highly symmetrical fashion. This report significantly expands the diversity and understanding of known CuA sites.
Asunto(s)
Proteínas Bacterianas/química , Cobre , Electrones , Multimerización de Proteína , Proteínas Bacterianas/metabolismo , Modelos Moleculares , Estructura Cuaternaria de ProteínaRESUMEN
Carbapenems are "last resort" ß-lactam antibiotics used to treat serious and life-threatening health care-associated infections caused by multidrug-resistant Gram-negative bacteria. Unfortunately, the worldwide spread of genes coding for carbapenemases among these bacteria is threatening these life-saving drugs. Metallo-ß-lactamases (MßLs) are the largest family of carbapenemases. These are Zn(II)-dependent hydrolases that are active against almost all ß-lactam antibiotics. Their catalytic mechanism and the features driving substrate specificity have been matter of intense debate. The active sites of MßLs are flanked by two loops, one of which, loop L3, was shown to adopt different conformations upon substrate or inhibitor binding, and thus are expected to play a role in substrate recognition. However, the sequence heterogeneity observed in this loop in different MßLs has limited the generalizations about its role. Here, we report the engineering of different loops within the scaffold of the clinically relevant carbapenemase NDM-1. We found that the loop sequence dictates its conformation in the unbound form of the enzyme, eliciting different degrees of active-site exposure. However, these structural changes have a minor impact on the substrate profile. Instead, we report that the loop conformation determines the protonation rate of key reaction intermediates accumulated during the hydrolysis of different ß-lactams in all MßLs. This study demonstrates the existence of a direct link between the conformation of this loop and the mechanistic features of the enzyme, bringing to light an unexplored function of active-site loops on MßLs.
Asunto(s)
Antibacterianos/química , Ceftazidima/química , Imipenem/química , Meropenem/química , Zinc/química , beta-Lactamasas/química , Secuencia de Aminoácidos , Antibacterianos/metabolismo , Dominio Catalítico , Cefepima/química , Cefepima/metabolismo , Cefotaxima/química , Cefotaxima/metabolismo , Ceftazidima/metabolismo , Clonación Molecular , Cristalografía por Rayos X , Escherichia coli/genética , Escherichia coli/metabolismo , Expresión Génica , Vectores Genéticos/química , Vectores Genéticos/metabolismo , Imipenem/metabolismo , Cinética , Meropenem/metabolismo , Modelos Moleculares , Piperacilina/química , Piperacilina/metabolismo , Unión Proteica , Conformación Proteica en Hélice alfa , Conformación Proteica en Lámina beta , Ingeniería de Proteínas , Dominios y Motivos de Interacción de Proteínas , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Especificidad por Sustrato , Zinc/metabolismo , Resistencia betalactámica , beta-Lactamasas/genética , beta-Lactamasas/metabolismoRESUMEN
Here we report the spectroscopic and electrochemical characterization of three novel chimeric CuA proteins in which either one or the three loops surrounding the metal ions in the Thermus thermophilus protein have been replaced by homologous human and plant sequences while preserving the set of coordinating amino acids. These conservative modifications mimic basic differences between CuA sites from different organisms and allow for fine tuning the energy gap between alternative electronic ground states of CuA.. This results in a systematic modulation of thermodynamic and kinetic electron transfer (ET) parameters and in the selection of one of two possible redox-active molecular orbitals, which differ in the ET reorganization energy by a factor of 2. Moreover, the ET mechanism is found to be frictionally controlled, and the modifications introduced into the different chimeras do not affect the frictional activation parameter.
Asunto(s)
Cobre/metabolismo , Complejo IV de Transporte de Electrones/metabolismo , Thermus thermophilus/metabolismo , Cobre/química , Cristalografía por Rayos X , Técnicas Electroquímicas , Transporte de Electrón , Complejo IV de Transporte de Electrones/química , Cinética , Modelos Moleculares , Termodinámica , Thermus thermophilus/químicaRESUMEN
CuA centers perform efficient long-range electron transfer. The electronic structure of native CuA sites can be described by a double-potential well with a dominant σu* ground state in fast equilibrium with a less populated πu ground state. Here, we report a CuA mutant in which a lysine was introduced in the axial position. This results in a highly unstable protein with a pH-dependent population of the two ground states. Deep analysis of the high-pH form of this variant shows the stabilization of the πu ground state due to direct binding of the Lys residue to the copper center that we attribute to deprotonation of this residue.