Structure of MltG from Mycobacterium abscessus reveals structural plasticity between composed domains.

MltG, a membrane-bound lytic transglycosylase, has roles in terminating glycan polymerization in peptidoglycan and incorporating glycan chains into the cell wall, making it significant in bacterial cell-wall biosynthesis and remodeling. This study provides the first reported MltG structure from Mycobacterium abscessus (maMltG), a superbug that has high antibiotic resistance. Our structural and biochemical analyses revealed that MltG has a flexible peptidoglycan-binding domain and exists as a monomer in solution. Further, the putative active site of maMltG was disclosed using structural analysis and sequence comparison. Overall, this study contributes to our understanding of the transglycosylation reaction of the MltG family, aiding the design of next-generation antibiotics targeting M. abscessus.

Catalytic Activity of Incorporated Palladium Nanoparticles on Recycled Carbon Black from Scrap Tires.

A stable support substrate for catalytically active metal nanoparticles (NPs) plays an important role in various chemical transformation reactions. This study describes the effective integration of catalytically active palladium nanoparticles (PdNPs) into recycled carbon black (rCB) obtained from scrap tires. The loading efficiency and dispersion degree of PdNPs prepared via a deposition-precipitation method are thoroughly compared to those prepared with conventional Vulcan CB. As the rCB powder exhibits relatively larger surface areas and wider pore size distributions, slightly polydisperse and more PdNPs are integrated across rCB than those on CB. These composite materials are subsequently tested as catalysts in the Suzuki coupling and styrene hydrogenation reactions. For the Suzuki reaction using phenylboronic acid and bromobenzene, the PdNPs on rCB exhibit slightly higher reactivity than those on CB (TOF of ∼9/h vs ∼8/h), presumably due to the structural features of the integrated PdNPs and the relatively hydrophobic characteristics of the rCB substrate. For the hydrogenation reaction, both composite materials easily result in over 99% yield under ambient conditions with similar activation energies of ∼32 kcal/mol. These composite materials are also recyclable in both reactions without a detectable loss of the PdNP catalyst and its activity. Understanding the physicochemical properties of rCB and demonstrating their potential use as a catalyst support substrate evidently suggest the possibility of replacing conventional CB, which also provides an idea of upcycling waste tires in the development of practical and green reaction systems.

Structural basis of Cas3 activation in type I-C CRISPR-Cas system.

CRISPR-Cas systems function as adaptive immune mechanisms in bacteria and archaea and offer protection against phages and other mobile genetic elements. Among many types of CRISPR-Cas systems, Type I CRISPR-Cas systems are most abundant, with target interference depending on a multi-subunit, RNA-guided complex known as Cascade that recruits a transacting helicase nuclease, Cas3, to degrade the target. While structural studies on several other types of Cas3 have been conducted long ago, it was only recently that the structural study of Type I-C Cas3 in complex with Cascade was revealed, shedding light on how Cas3 achieve its activity in the Cascade complex. In the present study, we elucidated the first structure of standalone Type I-C Cas3 from Neisseria lactamica (NlaCas3). Structural analysis revealed that the histidine-aspartate (HD) nuclease active site of NlaCas3 was bound to two Fe2+ ions that inhibited its activity. Moreover, NlaCas3 could cleave both single-stranded and double-stranded DNA in the presence of Ni2+ or Co2+, showing the highest activity in the presence of both Ni2+ and Mg2+ ions. By comparing the structural studies of various Cas3 proteins, we determined that our NlaCas3 stays in an inactive conformation, allowing us to understand the structural changes associated with its activation and their implication.

Structural analysis of a bacterial ankyrin-like protein secreted by Acinetobacter baumannii.

In bacteria, the ankyrin-like protein AnkB helps overcome stress by regulating catalase activity when expressed under stressful conditions. As the structural properties of AnkB are largely unexplored, our understanding of various AnkB-mediated functions in bacteria remains limited. In the present study, we describe the structure of AnkB from Acinetobacter baumannii, hereafter referred to as "AbAnkB," which has a unique tertiary configuration compared with that of other ankyrin domain-containing proteins. Structural analysis revealed that AbAnkB has a relatively long loop between AKR3 and AKR4 and an oppositely positioned α8 helix. Based on amino acid conservation and protein surface analyses, we identified a hydrophobic patch that might be critical for the function of AbAnkB. To the best of our knowledge, our study is the first to report the structure of a bacterial AnkB protein; our findings will markedly enhance our understanding of its functions in bacteria.

Fully closed conformation of penicillin-binding protein revealed by structure of PBP2 from Acinetobacter baumannii.

Penicillin-binding protein 2 (PBP2), a vital protein involved in bacterial cell-wall synthesis, serves a target for ß-lactam antibiotics. Acinetobacter baumannii is a pathogen notorious for multidrug resistance; therefore, exploration of PBPs is pivotal in the development of new antimicrobial strategies. In this study, the tertiary structure of PBP2 from A. baumannii (abPBP2) was elucidated using X-ray crystallography. The structural analysis demonstrated notable movement in the head domain, potentially critical for its glycosyltransferase function, suggesting that abPBP2 assumes a fully closed conformation. Our findings offer valuable information for developing novel antimicrobial agents targeting abPBP2 that are applicable in combating multidrug-resistant infections.

Structure, dimeric conformation, and coenzyme versatility of p-hydroxybenzoate hydroxylase from Arthrobacter sp. PAMC25564.

p-Hydroxybenzoate hydroxylase (PHBH) catalyzes the ortho-hydroxylation of 4-hydroxybenzoate (4-HB) to protocatechuate (PCA). PHBHs are commonly known as homodimers, and the prediction of pyridine nucleotide binding and specificity remains an ongoing focus in this field. Therefore, our study aimed to determine the dimerization interface in AspPHBH from Arthrobacter sp. PAMC25564 and identify the canonical pyridine nucleotide-binding residues, along with coenzyme specificity, through site-directed mutagenesis. The results confirm a functional dimeric assembly from a tetramer that appeared in the crystallographic asymmetric unit identical to that established in previous studies. Furthermore, AspPHBH exhibits coenzyme versatility, utilizing both NADH and NADPH, with a preference for NADH. Rational engineering experiments demonstrated that targeted mutations in coenzyme surrounding residues profoundly impact NADPH binding, leading to nearly abrogated enzymatic activity compared to that of NADH. R50, R273, and S166 emerged as significant residues for NAD(P)H binding, having a near-fatal impact on NADPH binding compared to NADH. Likewise, the E44 residue plays a critical role in determining coenzyme specificity. Overall, our findings contribute to the fundamental understanding of the determinants of PHBH's active dimeric conformation, coenzyme binding and specificity holding promise for biotechnological advancements.

Interdomain flexibility and putative active site was revealed by crystal structure of MltG from Acinetobacter baumannii.

MltG, positioned within the inner membrane of bacteria, functions as a lytic transglycosylase (LT) essential for integrating into the cell wall by cleaving the newly synthesized glycan strand, emphasizing its critical involvement in bacterial cell wall biosynthesis and remodeling. Current study reported the first structure of MltG family of LT. We have elucidated the structure of MltG from Acinetobacter baumannii (abMltG), a formidable superbug renowned for its remarkable antibiotic resistance. Our structural and biochemical investigations unveiled the presence of a flexible peptidoglycan (PG)-binding domain (PGD) within MltG family, which exists as a monomer in solution. Furthermore, we delineated the putative active site of abMltG via a combination of structural analysis and sequence comparison. This discovery enhances our comprehension of the transglycosylation process mediated by the MltG family, offering insights that could inform the development of novel antibiotics tailored to combat A. baumannii.

Electromagnetic Interference Shielding Properties of Highly Flexible Poly(styrene-co-butyl acrylate)/PEDOT:PSS Films Fabricated by Latex Technology.

As the use of stretchable electronic devices increases, the importance of flexible electromagnetic interference (EMI) shielding films is emerging. In this study, a highly flexible shielding film was fabricated using poly(styrene-co-butyl acrylate) (p(St-co-BA)) latex as a matrix and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a conductive filler, and then the mechanical properties and EMI shielding performance of the film were examined. Styrene and butyl acrylate were copolymerized to lower the high glass transition temperature and increase the ductility of brittle polystyrene. The latex blending technique was used to produce a shielding film in which the aqueous filler dispersion was uniformly dispersed in the emulsion polymerized resin. To determine the phase change in the copolymer matrix with temperature, the storage modulus was measured, and a time-temperature superposition master curve was constructed. The drying temperature of water-based copolymer resin suitable for film fabrication was set based on this curve. The glass transition temperature and flexibility of the blends were determined by evaluating the thermomechanical analysis and tensile tests. The EMI shielding effectiveness (SE) of the films was analyzed at frequencies from 50 MHz to 1.5 GHz, covering the VHF and UHF ranges. As the filler content increased, the SE of the blend film increased, but the elongation increased until a certain content and then decreased. The optimal content of PEDOT:PSS that satisfied both the ductility and shielding performance of the film was found to be 10 wt%. In this case, the elongation at break reached 300%, and the SE of a 1.6 mm thick film was about 35 dB. The film developed in this study can be used as an EMI shielding material that requires high flexibility.

AcrIIA28 is a metalloprotein that specifically inhibits targeted-DNA loading to SpyCas9 by binding to the REC3 domain.

CRISPR-Cas systems serve as adaptive immune systems in bacteria and archaea, protecting against phages and other mobile genetic elements. However, phages and archaeal viruses have developed countermeasures, employing anti-CRISPR (Acr) proteins to counteract CRISPR-Cas systems. Despite the revolutionary impact of CRISPR-Cas systems on genome editing, concerns persist regarding potential off-target effects. Therefore, understanding the structural and molecular intricacies of diverse Acrs is crucial for elucidating the fundamental mechanisms governing CRISPR-Cas regulation. In this study, we present the structure of AcrIIA28 from Streptococcus phage Javan 128 and analyze its structural and functional features to comprehend the mechanisms involved in its inhibition of Cas9. Our current study reveals that AcrIIA28 is a metalloprotein that contains Zn2+ and abolishes the cleavage activity of Cas9 only from Streptococcus pyrogen (SpyCas9) by directly interacting with the REC3 domain of SpyCas9. Furthermore, we demonstrate that the AcrIIA28 interaction prevents the target DNA from being loaded onto Cas9. These findings indicate the molecular mechanisms underlying AcrIIA28-mediated Cas9 inhibition and provide valuable insights into the ongoing evolutionary battle between bacteria and phages.

Novel structure of the anti-CRISPR protein AcrIE3 and its implication on the CRISPR-Cas inhibition.

As a response to viral infections, bacteria have evolved the CRISPR-Cas system as an adaptive immune mechanism, enabling them to target and eliminate viral genetic material introduced during infection. However, viruses have also evolved mechanisms to counteract this bacterial defense, including anti-CRISPR proteins, which can inactivate the CRISPR-Cas adaptive immune system, thus aiding the viruses in their survival and replication within bacterial hosts. In this study, we establish the high-resolution crystal structure of the Type IE anti-CRISPR protein, AcrIE3. Our structural examination showed that AcrIE3 adopts a helical bundle fold comprising four α-helices, with a notably extended loop at the N-terminus. Additionally, surface analysis of AcrIE3 revealed the presence of three acidic regions, which potentially play a crucial role in the inhibitory function of this protein. The structural information we have elucidated for AcrIE3 will provide crucial insights into fully understanding its inhibitory mechanism. Furthermore, this information is anticipated to be important for the application of the AcrIE family in genetic editing, paving the way for advancements in gene editing technologies.

Novel structure of secreted small molecular weight antigen Mtb12 from Mycobacterium tuberculosis.

Mtb12, a small protein secreted by Mycobacterium tuberculosis, is known to elicit immune responses in individuals infected with the pathogen. It serves as an antigen recognized by the host's immune system. Due to its immunogenic properties and pivotal role in tuberculosis (TB) pathogenesis, Mtb12 is considered a promising candidate for TB diagnosis and vaccine development. However, the structural and functional properties of Mtb12 are largely unexplored, representing a significant gap in our understanding of M. tuberculosis biology. In this study, we present the first structure of Mtb12, which features a unique tertiary configuration consisting of four beta strands and four alpha helices. Structural analysis reveals that Mtb12 has a surface adorned with a negatively charged pocket adjacent to a central cavity. The features of these structural elements and their potential effects on the function of Mtb12 warrant further exploration. These findings offer valuable insights for vaccine design and the development of diagnostic tools.

TRAF1 from a Structural Perspective.

Tumor necrosis factor receptor-associated factor (TRAF) proteins play pivotal roles in a multitude of cellular signaling pathways, encompassing immune response, cell fate determination, development, and thrombosis. Their involvement in these processes hinges largely on their ability to interact directly with diverse receptors via the TRAF domain. Given the limited binding interface, understanding how specific TRAF domains engage with various receptors and how structurally similar binding interfaces of TRAF family members adapt their distinct binding partners has been the subject of extensive structural investigations over several decades. This review presents an in-depth exploration of the current insights into the structural and molecular diversity exhibited by the TRAF domain and TRAF-binding motifs across a range of receptors, with a specific focus on TRAF1.

The structure of MucD from Pseudomonas syringae revealed N-terminal loop-mediated trimerization of HtrA-like serine protease.

Protein quality control mechanisms are essential for maintaining cellular integrity, and the HtrA family of serine proteases plays a crucial role in handling folding stress in prokaryotic periplasm. Escherichia coli harbors three HtrA members, namely, DegS, DegP, and DegQ, which share a common domain structure. MucD, a putative HtrA family member that resembles DegP, is involved in alginate biosynthesis regulation and the stress response. Pseudomonas syringae causes plant diseases and opportunistic infections in humans. This study presents the high-resolution structure of MucD from Pseudomonas syringae (psMucD), revealing its composition as a typical HtrA family serine protease with protease and PDZ domains. Its findings suggest that psMucD containing one PDZ domain is a trimer in solution, and psMucD trimerization is mediated by its N-terminal loop. Sequence and structural analyses revealed similarities and differences with other HtrA family members. Additionally, this study provides a model of psMucD's catalytic process, comparing it with other members of the HtrA family of serine proteases.

Cyclosporin A inhibits prostate cancer growth through suppression of E2F8 transcription factor in a MELK­dependent manner.

The treatment of advanced prostate cancer remains a formidable challenge due to the limited availability of effective treatment options. Therefore, it is imperative to identify promising druggable targets that provide substantial clinical benefits and to develop effective treatment strategies to overcome therapeutic resistance. Cyclosporin A (CsA) showed an anticancer effect on prostate cancer in cultured cell and xenograft models. E2F8 was identified as a master transcription factor that regulated a clinically significant CsA specific gene signature. The expression of E2F8 increased during prostate cancer progression and high levels of E2F8 expression are associated with a poor prognosis in patients with prostate cancer. MELK was identified as a crucial upstream regulator of E2F8 expression through the transcriptional regulatory network and Bayesian network analyses. Knockdown of E2F8 or MELK inhibited cell growth and colony formation in prostate cancer cells. High expression levels of E2F8 and androgen receptor (AR) are associated with a worse prognosis in patients with prostate cancer compared with low levels of both genes. The inhibition of E2F8 improved the response to AR blockade therapy. These results suggested that CsA has potential as an effective anticancer treatment for prostate cancer, while also revealing the oncogenic role of E2F8 and its association with clinical outcomes in prostate cancer. These results provided valuable insight into the development of therapeutic and diagnostic approaches for prostate cancer.

Structural basis of IRGB10 oligomerization by GTP hydrolysis.

Immunity-related GTPase B10 (IRGB10) is a crucial member of the interferon (IFN)-inducible GTPases and plays a vital role in host defense mechanisms. Following infection, IRGB10 is induced by IFNs and functions by liberating pathogenic ligands to activate the inflammasome through direct disruption of the pathogen membrane. Despite extensive investigation into the significance of the cell-autonomous immune response, the precise molecular mechanism underlying IRGB10-mediated microbial membrane disruption remains elusive. Herein, we present two structures of different forms of IRGB10, the nucleotide-free and GppNHp-bound forms. Based on these structures, we identified that IRGB10 exists as a monomer in nucleotide-free and GTP binding states. Additionally, we identified that GTP hydrolysis is critical for dimer formation and further oligomerization of IRGB10. Building upon these observations, we propose a mechanistic model to elucidate the working mechanism of IRGB10 during pathogen membrane disruption.

The structure of AcrIC9 revealing the putative inhibitory mechanism of AcrIC9 against the type IC CRISPR-Cas system.

CRISPR-Cas systems are known to be part of the bacterial adaptive immune system that provides resistance against intruders such as viruses, phages and other mobile genetic elements. To combat this bacterial defense mechanism, phages encode inhibitors called Acrs (anti-CRISPR proteins) that can suppress them. AcrIC9 is the most recently identified member of the AcrIC family that inhibits the type IC CRISPR-Cas system. Here, the crystal structure of AcrIC9 from Rhodobacter capsulatus is reported, which comprises a novel fold made of three central antiparallel ß-strands surrounded by three α-helixes, a structure that has not been detected before. It is also shown that AcrIC9 can form a dimer via disulfide bonds generated by the Cys69 residue. Finally, it is revealed that AcrIC9 directly binds to the type IC cascade. Analysis and comparison of its structure with structural homologs indicate that AcrIC9 belongs to DNA-mimic Acrs that directly bind to the cascade complex and hinder the target DNA from binding to the cascade.

Structure of YdjH from Acinetobacter baumannii revealed an active site of YdjH family sugar kinase.

Bacterial sugar kinase is a central enzyme for proper sugar degradation in bacteria, essential for survival and growth. Therefore, this enzyme family is a primary target for antibacterial drug development, with YdjH most preferring to phosphorylate higher-order monosaccharides with a carboxylate terminus. Sugar kinases express diverse specificity and functions, making specificity determination of this family a prominent issue. This study examines the YdjH crystal structure from Acinetobacter baumannii (abYdjH), which has an exceptionally high antibiotic resistance and is considered a superbug. Our structural and biochemical study revealed that abYdjH has a widely open lid domain and is a solution dimer. In addition, the putative active site of abYdjH was determined based on structural analysis, sequence comparison, and in silico docking. Finally, we proposed the active site-forming residues that determine various sugar specificities from abYdjH. This study contributes towards a deeper understanding of the phosphorylation process and bacterial sugar metabolism of YdjH family to design the next-generation antibiotics for targeting A. baumannii.

Comparison of the structure and activity of thioredoxin 2 and thioredoxin 1 from Acinetobacter baumannii.

Thioredoxin (Trx) is essential in a redox-control system, with many bacteria containing two Trxs: Trx1 and Trx2. Due to a Trx system's critical function, Trxs are targets for novel antibiotics. Here, a 1.20 Šhigh-resolution structure of Trx2 from Acinetobacter baumannii (abTrx2), an antibiotic resistant pathogenic superbug, is elucidated. By comparing Trx1 and Trx2, it is revealed that the two Trxs possess similar activity, although Trx2 contains an additional N-terminal zinc-finger domain and exhibits more flexible properties in solution. Finally, it is shown that the Trx2 zinc-finger domain might be rotatable and that proper zinc coordination at the zinc-finger domain is critical to abTrx2 activity. This study enhances understanding of the Trx system and will facilitate the design of novel antibiotics.

Molecular basis of neurodevelopmental disorders caused by pathogenic variants of PIDD.

PIDDosome formation followed by caspase-2 activation is critical for genotoxic stress-induced apoptotic cell death. Failure of proper caspase-2 activation causes a neurodevelopmental disorder and intellectual disability. R815W, R862W, and Q863stop mutations in p53-induced protein with a death domain (PIDD), a component of the PIDDosome, also lead to this disorder. However, the molecular mechanisms underlying this pathogenesis remain elusive. In this study, we analyzed the molecular mechanisms underlying the pathogenesis of the PIDD DD pathogenic variants R815W, R862W, and Q863stop. We determined that these mutations prevented the interaction between PIDD and RIP-associated Ich-1/Ced-3 homologous protein with a death domain (RAIDD), a molecule that mediates PIDDosome formation. The disruption of this interaction affects PIDDosome formation and caspase-2 activation.