Cryo-EM structures of type IV pili complexed with nanobodies reveal immune escape mechanisms.

Type IV pili (T4P) are prevalent, polymeric surface structures in pathogenic bacteria, making them ideal targets for effective vaccines. However, bacteria have evolved efficient strategies to evade type IV pili-directed antibody responses. Neisseria meningitidis are prototypical type IV pili-expressing Gram-negative bacteria responsible for life threatening sepsis and meningitis. This species has evolved several genetic strategies to modify the surface of its type IV pili, changing pilin subunit amino acid sequence, nature of glycosylation and phosphoforms, but how these modifications affect antibody binding at the structural level is still unknown. Here, to explore this question, we determine cryo-electron microscopy (cryo-EM) structures of pili of different sequence types with sufficiently high resolution to visualize posttranslational modifications. We then generate nanobodies directed against type IV pili which alter pilus function in vitro and in vivo. Cyro-EM in combination with molecular dynamics simulation of the nanobody-pilus complexes reveals how the different types of pili surface modifications alter nanobody binding. Our findings shed light on the impressive complementarity between the different strategies used by bacteria to avoid antibody binding. Importantly, we also show that structural information can be used to make informed modifications in nanobodies as countermeasures to these immune evasion mechanisms.

Structural and Biochemical Features of OXA-517: a Carbapenem and Expanded-Spectrum Cephalosporin Hydrolyzing OXA-48 Variant.

OXA-48-producing Enterobacterales have now widely disseminated throughout the world. Several variants have now been reported, differing by just a few amino-acid substitutions or deletions, mostly in the region of the loop ß5-ß6. As OXA-48 hydrolyzes carbapenems but lacks significant expanded-spectrum cephalosporin (ESC) hydrolytic activity, ESCs were suggested as a therapeutic option. Here, we have characterized OXA-517, a natural variant of OXA-48- with an Arg214Lys substitution and a deletion of Ile215 and Glu216 in the ß5-ß6 loop, capable of hydrolyzing at the same time ESC and carbapenems. MICs values of E. coli expressing blaOXA-517 gene revealed reduced susceptibility to carbapenems (similarly to OXA-48) and resistance to ESCs. Steady-state kinetic parameters revealed high catalytic efficiencies for ESCs and carbapenems. The blaOXA-517 gene was located on a ca. 31-kb plasmid identical to the prototypical IncL blaOXA-48-carrying plasmid except for an IS1R-mediated deletion of 30.7-kb in the tra operon. The crystal structure of OXA-517, determined to 1.86 Å resolution, revealed an expanded active site compared to that of OXA-48, which allows for accommodation of the bulky ceftazidime substrate. Our work illustrates the remarkable propensity of OXA-48-like carbapenemases to evolve through mutation/deletion in the ß5-ß6 loop to extend its hydrolysis profile to encompass most ß-lactam substrates.

Azetidinimines as a novel series of non-covalent broad-spectrum inhibitors of ß-lactamases with submicromolar activities against carbapenemases KPC-2 (class A), NDM-1 (class B) and OXA-48 (class D).

The occurrence of resistances in Gram negative bacteria is steadily increasing to reach extremely worrying levels and one of the main causes of resistance is the massive spread of very efficient ß-lactamases which render most ß-lactam antibiotics useless. Herein, we report the development of a series of imino-analogues of ß-lactams (namely azetidinimines) as efficient non-covalent inhibitors of ß-lactamases. Despite the structural and mechanistic differences between serine-ß-lactamases KPC-2 and OXA-48 and metallo-ß-lactamase NDM-1, all three enzymes can be inhibited at a submicromolar level by compound 7dfm, which can also repotentiate imipenem against a resistant strain of Escherichia coli expressing NDM-1. We show that 7dfm can efficiently inhibit not only the three main clinically-relevant carbapenemases of Ambler classes A (KPC-2), B (NDM-1) and D (OXA-48) with Ki's below 0.3 µM, but also the cephalosporinase CMY-2 (class C, 86% inhibition at 10 µM). Our results pave the way for the development of a new structurally original family of non-covalent broad-spectrum inhibitors of ß-lactamases.

Substrate Specificity of OXA-48 after ß5-ß6 Loop Replacement.

OXA-48 carbapenemase has rapidly spread in many countries worldwide with several OXA-48-variants being described, differing by a few amino acid (AA) substitutions or deletions, mostly in the ß5-ß6 loop. While single AA substitutions have only a minor impact on OXA-48 hydrolytic profiles, others with 4 AA deletions result in loss of carbapenem hydrolysis and gain of expanded-spectrum cephalosporin (ESC) hydrolysis. We have replaced the ß5-ß6 loop of OXA-48 with that of OXA-18, a clavulanic-acid inhibited oxacillinase capable of hydrolyzing ESCs but not carbapenems. The hybrid enzyme OXA-48Loop18 was able to hydrolyze ESCs and carbapenems (although with a lower kcat), even though the ß5-ß6 loop was longer and its sequence quite different from that of OXA-48. The kinetic parameters of OXA-48Loop18 were in agreement with the MIC values. X-ray crystallography and molecular modeling suggest that the conformation of the grafted loop allows the binding of bulkier substrates, unlike that of the native loop, expanding the hydrolytic profile. This seems to be due not only to differences in AA sequence, but also to the backbone conformation the loop can adopt. Finally, our results provide further experimental evidence for the role of the ß5-ß6 loop in substrate selectivity of OXA-48-like enzymes and additional details on the structure-function relationship of ß-lactamases, demonstrating how localized changes in these proteins can alter or expand their function, highlighting their plasticity.

Unravelling ceftazidime/avibactam resistance of KPC-28, a KPC-2 variant lacking carbapenemase activity.

BACKGROUND: KPC-like carbapenemases have spread worldwide with more than 30 variants identified that differ by single or double amino-acid substitutions. OBJECTIVES: To describe the steady-state kinetic parameters of KPC-28, which differs from KPC-2 by a H274Y substitution and the deletion of two amino acids (Δ242-GT-243). METHODS: The blaKPC-2, blaKPC-3, blaKPC-14 and blaKPC-28 genes were cloned into a pTOPO vector for susceptibility testing or into pET41b for overexpression, purification and subsequent kinetic parameter (Km, kcat) determination. Molecular docking experiments were performed to explore the role of the amino-acid changes in the carbapenemase activity. RESULTS: Susceptibility testing revealed that Escherichia coli producing KPC-28 displayed MICs that were lower for carbapenems and higher for ceftazidime and ceftazidime/avibactam as compared with KPC-2. The catalytic efficiencies of KPC-28 and KPC-14 for imipenem were 700-fold and 200-fold lower, respectively, than those of KPC-2, suggesting that Δ242-GT-243 in KPC-28 and KPC-14 is responsible for reduced carbapenem hydrolysis. Similarly, the H274Y substitution resulted in KPC-28 in a 50-fold increase in ceftazidime hydrolysis that was strongly reversed by clavulanate. CONCLUSIONS: We have shown that KPC-28 lacks carbapenemase activity, has increased ceftazidime hydrolytic activity and is strongly inhibited by clavulanate. KPC-28-producing E. coli isolates display an avibactam-resistant ESBL profile, which may be wrongly identified by molecular and immunochromatographic assays as the presence of a carbapenemase. Accordingly, confirmation of carbapenem hydrolysis will be mandatory with assays based solely on blaKPC gene or gene product detection.

Genetic, Biochemical, and Structural Characterization of CMY-136 ß-Lactamase, a Peculiar CMY-2 Variant.

With the widespread use and abuse of antibiotics for the past decades, antimicrobial resistance poses a serious threat to public health nowadays. ß-Lactams are the most used antibiotics, and ß-lactamases are the most widespread resistance mechanism. Class C ß-lactamases, also known as cephalosporinases, usually do not hydrolyze the latest and most potent ß-lactams, expanded spectrum cephalosporins and carbapenems. However, the recent emergence of extended-spectrum AmpC cephalosporinases, their resistance to inhibition by classic ß-lactamase inhibitors, and the fact that they can contribute to carbapenem resistance when paired with impermeability mechanisms, means that these enzymes may still prove worrisome in the future. Here we report and characterize the CMY-136 ß-lactamase, a Y221H point mutant derivative of CMY-2. CMY-136 confers an increased level of resistance to ticarcillin, cefuroxime, cefotaxime, and ceftolozane/tazobactam. It is also capable of hydrolyzing ticarcillin and cloxacillin, which act as inhibitors of CMY-2. X-ray crystallography and modeling experiments suggest that the hydrolytic profile alterations seem to be the result of an increased flexibility and altered conformation of the Ω-loop, caused by the Y221H mutation.

Genetic and Biochemical Characterization of OXA-519, a Novel OXA-48-Like ß-Lactamase.

A multidrug-resistant Klebsiella pneumoniae 1210 isolate with reduced carbapenem susceptibility revealed the presence of a novel plasmid-encoded blaOXA-48-like gene, named blaOXA-519 The 60.7-kb plasmid (pOXA-519) was similar to the IncL-OXA-48 prototypical plasmid except for a ca. 2-kb deletion due to an IS1R insertion. OXA-519 differed from OXA-48 by a Val120Leu substitution, which resulted in an overall reduced ß-lactam-hydrolysis profile, except those for ertapenem and meropenem, which were increased. Thus, detection of OXA-519 producers using biochemical tests that monitor imipenem hydrolysis will be difficult.

Blinded evaluation of farnesoid X receptor (FXR) ligands binding using molecular docking and free energy calculations.

Our participation to the D3R Grand Challenge 2 involved a protocol in two steps, with an initial analysis of the available structural data from the PDB allowing the selection of the most appropriate combination of docking software and scoring function. Subsequent docking calculations showed that the pose prediction can be carried out with a certain precision, but this is dependent on the specific nature of the ligands. The correct ranking of docking poses is still a problem and cannot be successful in the absence of good pose predictions. Our free energy calculations on two different subsets provided contrasted results, which might have the origin in non-optimal force field parameters associated with the sulfonamide chemical moiety.

A Modular Receptor Platform To Expand the Sensing Repertoire of Bacteria.

Engineered bacteria promise to revolutionize diagnostics and therapeutics, yet many applications are precluded by the limited number of detectable signals. Here we present a general framework to engineer synthetic receptors enabling bacterial cells to respond to novel ligands. These receptors are activated via ligand-induced dimerization of a single-domain antibody fused to monomeric DNA-binding domains (split-DBDs). Using E. coli as a model system, we engineer both transmembrane and cytosolic receptors using a VHH for ligand detection and demonstrate the scalability of our platform by using the DBDs of two different transcriptional regulators. We provide a method to optimize receptor behavior by finely tuning protein expression levels and optimizing interdomain linker regions. Finally, we show that these receptors can be connected to downstream synthetic gene circuits for further signal processing. The general nature of the split-DBD principle and the versatility of antibody-based detection should support the deployment of these receptors into various hosts to detect ligands for which no receptor is found in nature.

Beta-lactamase database (BLDB) - structure and function.

Beta-Lactamase Database (BLDB) is a comprehensive, manually curated public resource providing up-to-date structural and functional information focused on this superfamily of enzymes with a great impact on antibiotic resistance. All the enzymes reported and characterised in the literature are presented according to the class (A, B, C and D), family and subfamily to which they belong. All three-dimensional structures of ß-lactamases present in the Protein Data Bank are also shown. The characterisation of representative mutants and hydrolytic profiles (kinetics) completes the picture and altogether these four elements constitute the essential foundation for a better understanding of the structure-function relationship within this enzymes family. BLDB can be queried using different protein- and nucleotide-based BLAST searches, which represents a key feature of particular importance in the context of the surveillance of the evolution of the antibiotic resistance. BLDB is available online at http://bldb.eu without any registration and supports all modern browsers.

Screening assay for inhibitors of a recombinant Streptococcus pneumoniae UDP-glucose pyrophosphorylase.

The UDP-glucose pyrophosphorylase of Streptococcus pneumoniae (GalUSpn) is absolutely required for the biosynthesis of capsular polysaccharide, the sine qua non virulence factor of pneumococcus. Since the eukaryotic enzymes are completely unrelated to their prokaryotic counterparts, we propose that the GalU enzyme is a critical target to fight the pneumococcal disease. A recombinant GalUSpn was overexpressed and purified. An enzymatic assay that is rapid, sensitive and easy to perform was developed. This assay was appropriate for screening chemical libraries for searching GalU inhibitors. This work represents a fundamental step in the exploration of novel antipneumococcal drugs.

Heidegger in Nishida Philosophy / Heidegger na Filosofia nishidiana

Nishida Kitaro (1870-1945) was one of the introducers of phenomenology in Japan. However, for him, there were points of disagreement with the statements of philosophy. In his encounter with the writings of Heidegger, the author also presents points to itself unacceptable or, at least, unsatisfied. In this work, we chose some critical views of the philosophical stance of Heidegger, between 1925 and 1940. The presentation will focus the historicity of the existence, based on texts and how Nishida discusses Heidegger's position on this issue.

Nishida Kitaro (1870-1945) foi um dos introdutores da fenomenologia no ambiente acadêmico japonês. No entanto, a partir de seu próprio ponto de vista, foram encontrados pontos de discordância com as afirmações da filosofia. Em seu encontro com os textos de Heidegger, o autor também detecta pontos que ele são inaceitáveis ou que o deixam insatisfeito. Neste trabalho, escolhemos algumas das críticas de Nishida à postura filosófica de Heidegger, entre 1925 e 1940. A apresentação terá como ponto central a historicidade da existência, focalizada a partir de textos de Nishida e o modo como problematiza a posição de Heidegger sobre esse tema.

Heidegger in Nishida Philosophy / Heidegger na Filosofia nishidiana

Nishida Kitaro (1870-1945) was one of the introducers of phenomenology in Japan. However, for him, there were points of disagreement with the statements of philosophy. In his encounter with the writings of Heidegger, the author also presents points to itself unacceptable or, at least, unsatisfied. In this work, we chose some critical views of the philosophical stance of Heidegger, between 1925 and 1940. The presentation will focus the historicity of the existence, based on texts and how Nishida discusses Heidegger's position on this issue.(AU)

Nishida Kitaro (1870-1945) foi um dos introdutores da fenomenologia no ambiente acadêmico japonês. No entanto, a partir de seu próprio ponto de vista, foram encontrados pontos de discordância com as afirmações da filosofia. Em seu encontro com os textos de Heidegger, o autor também detecta pontos que ele são inaceitáveis ou que o deixam insatisfeito. Neste trabalho, escolhemos algumas das críticas de Nishida à postura filosófica de Heidegger, entre 1925 e 1940. A apresentação terá como ponto central a historicidade da existência, focalizada a partir de textos de Nishida e o modo como problematiza a posição de Heidegger sobre esse tema.(AU)