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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Evaluation of two inoculation routes of an adenovirus-mediated viral protein inhibitor in a Crimean-Congo hemorrhagic fever mouse model

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne nairovirus with a wide geographic spread that can cause severe and lethal disease. No specific medical countermeasures are approved to combat this illness. The CCHFV L protein contains an ovarian tumor (OTU) domain with a cysteine protease thought to modulate cellular immune responses by removing ubiquitin and ISG15 post-translational modifications from host and viral proteins. Viral deubiquitinases like CCHFV OTU are attractive drug targets, as blocking their activity may enhance cellular immune responses to infection, and potentially inhibit viral replication itself. We previously demonstrated that the engineered ubiquitin variant CC4 is a potent inhibitor of CCHFV replication in vitro. A major challenge of the therapeutic use of small protein inhibitors such as CC4 is their requirement for intracellular delivery, e.g., by viral vectors. In this study, we examined the feasibility of in vivo CC4 delivery by a replication-deficient recombinant adenovirus (Ad-CC4) in a lethal CCHFV mouse model. Since the liver is a primary target of CCHFV infection, we aimed to optimize delivery to this organ by comparing intravenous (tail vein) and intraperitoneal injection of Ad-CC4. While tail vein injection is a traditional route for adenovirus delivery, in our hands intraperitoneal injection resulted in higher and more widespread levels of adenovirus genome in tissues, including, as intended, the liver. However, despite promising in vitro results, neither route of in vivo CC4 treatment resulted in protection from a lethal CCHFV infection.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Continuous NF-κB pathway inhibition promotes expansion of human phenotypical hematopoietic stem/progenitor cells through metabolism regulation

Highlights: • Small molecular inhibition of NF-κB pathway efficiently expands human HSPCs. • NF-κB inhibition with TPCA-1 improves the self-renewal potential and biological function maintenance of expanded CD34{sup +} cells. • NF-κB pathway inhibition reprograms metabolism and enhances glycolysis. • Continuous NF-κB inhibition is required in the culture process to facilitate primitive HSC maintenance. Hematopoietic stem/progenitor cells (HSPCs) ex vivo expansion is critical in facilitating their widespread clinical application. NF-κB pathway is implicated in the energy homeostasis and metabolic adaptation. To explore the effect of NF-κB pathway on the ex vivo HSPC expansion and metabolism, the 50 nM–1 μM inhibitor of NF-κB pathway TPCA-1 was used to expand cord blood derived CD34{sup +} cells in serum-free culture. The expansion folds, function, mitochondrial profile and metabolism of HSPCs were determined. After 10 days of culture with 100 nM TPCA-1, the expansion of total cells CD34{sup +}CD38{sup −} cells and CD34{sup +}CD38{sup −}CD45RA{sup −}CD90{sup +}CD49f{sup +} cells were significantly increased compared to the cytokine priming alone. Notably, TPCA-1 treatment generated ~ 2-fold greater percentage of CD34{sup +}EPCR{sup +} and CD34{sup +}CD38{sup −}CD45RA{sup −}CD90{sup +}CD49f{sup +} cells compared to cytokine only conditions. Moreover, TPCA-1 expanded CD34{sup +} cells displayed enhanced serial colonies forming potential and secondary expansion capability. NF-κB inhibition increased the expression of self-renewal related genes, while downregulated the expression of mitochondrial biogenesis regulator (Pgc1α) and mitochondrial chaperones and proteases (ClpP, Hsp10, Hsp60). Mitochondrial mass and membrane potential were markedly decreased with TPCA-1 treatment, leading to the reduced mitochondrial reactive oxygen species (ROS) level in HSPCs. NF-κB inhibition displayed augmented glycolysis rate with compromising mitochondrial metabolism. This study demonstrated that NF-κB pathway inhibition improved glycolysis and limited ROS production that promoted the ex vivo expansion and maintenance of functional HSPCs.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Deubiquitinating enzyme USP46 suppresses the progression of hepatocellular carcinoma by stabilizing MST1

Highlights: • Low USP46 level is correlated with poor prognosis in HCC. • USP46 suppresses the proliferation and metastasis of HCC. • USP46 suppress the progression of HCC by inhibiting the expression of YAP1. • MST1 mediates the regulation of USP46 on YAP1. • USP46 stabilized MST1 protein through inhibiting its ubiquitination and degradation. The deubiquitinating enzyme USP46 (ubiquitin-specific protease 46) is implicated in various cancers. However, its role and regulatory mechanism in HCC (hepatocellular carcinoma) are still unknown. In this study, we showed that USP46 is downregulated in HCC tissues and that low USP46 levels are associated with poor prognosis in HCC patients. In functional experiments, overexpression of USP46 impaired proliferation and metastasis of HCC cells, whereas knockdown of USP46 enhanced cell proliferation and invasiveness in vitro and in vivo. Furthermore, we found that USP46 suppresses HCC cell proliferation and metastasis by inhibiting YAP1. Ectopic expression of YAP1 rescued the inhibition of cell proliferation and metastasis caused by USP46 overexpression. Mechanistically, USP46 promotes the degradation of YAP1 by increasing expression of MST1, and the increase in MST1 protein antagonizes YAP1 to suppress HCC progression. Finally, we demonstrated that USP46 stabilizes the MST1 protein by directly binding to it and decreasing its ubiquitination. Taken together, our results demonstrated that USP46 may be a novel tumor suppressor in HCC. Moreover, USP46 acts as a deubiquitinating enzyme of MST1 to potentiate MST1 kinase activity to suppress tumor growth and metastasis, indicating that USP46 activation may represent a potential treatment strategy for HCC.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

De-ubiquitination of p300 by USP12 Critically Enhances METTL3 Expression and Ang II-induced cardiac hypertrophy

Highlights: • The expression of USP12 is increased in Ang II-induced cardiac hypertrophy in vitro and in vivo. • USP12 aggravates Ang II-induced cardiomyocyte hypertrophy via upregulating METTL3. • USP12 promoted METTL3 expression via modulating p300. • USP12 suppresses the ubiquitination of p300 to block its degradation. Stresses, such as neurohumoral activation, induced pathological cardiac hypertrophy is the main risk factor for heart failure. The ubiquitin-proteasome system (UPS) plays a key role in maintaining protein homeostasis and cardiac function. However, research on the role and mechanism of deubiquitinating enzymes (DUBs) in cardiac hypertrophy is limited. Here, we observe that the deubiquitinating enzyme ubiquitin-specific protease 12(USP12) is upregulated in Ang II-induced hypertrophic hearts and primary neonatal rat cardiomyocytes (NRCMs). Inhibition of USP12 ameliorate Ang II-induced myocardial hypertrophy, while overexpression of USP12 have the opposite effect. USP12 deficiency also significantly attenuate the phenotype of Ang II-induced cardiac hypertrophy in vivo. Moreover, we demonstrate that USP12 aggravate Ang II-induced cardiac hypertrophy by enhancing METTL3, a methyltransferase which catalyze N{sup 6}-methyladenosine (m{sup 6}A) modification on messenger RNA and acts as a harmful factor in pathological cardiac hypertrophy. Upregulation of METTL3 reverse the reduction of myocardial hypertrophy induced by USP12 silencing in NRCMs. In contrast, knockdown of METTL3 attenuate the aggravation of myocardial hypertrophy in USP12-overexpressing NRCMs. Furthermore, we discover that USP12 promote the expression of METTL3 via upregulating p300. Mechanistically, USP12 binds and stabilizes p300, thereby activating the transcription of its downstream gene METTL3. Finally, our data show that USP12 is partially dependent on the stabilization of p300 to activate METTL3 expression and promote myocardial hypertrophy. Taken together, our results demonstrate that USP12 acts as a pro-hypertrophic deubiquitinating enzyme via enhancing p300/METTL3 axis, indicating that targeting USP12 could be a potential treatment strategy for pathological cardiac hypertrophy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

USP18 promotes tumor metastasis in esophageal squamous cell carcinomas via deubiquitinating ZEB1

Highlights: • High USP18 expression is positively correlated with the malignant phenotype and poor survival in ESCC patients. • Knockdown of USP18 suppressed the metastasis ability of ESCC cells in vitro and in vivo. • USP18 contributes to ESCC cell metastasis by inducing ZEB1 mediated EMT process. • USP18 acts as a deubiquitinase, and stabilises ZEB1 by reducing its poly-ubiquitination. The dysregulation of deubiquitinating enzymes (DUBs), which regulate the stability of most cellular proteins, have been implicated in many human diseases, including cancers. Ubiquitin-specific protease 18 (USP18), a member of the DUBs family, functions as a potential tumour promoter in various cancers. However, the biological function and clinical significance of USP18 in esophageal squamous cell carcinomas (ESCC) are still unclear. Here, we found that ESCC tumors had higher USP18 expression compared with that of normal esophageal epithelial tissues, and high USP18 level was significantly correlated with malignant phenotype and shorter survival in patients with ESCC. In functional experiments, USP18 knockdown significantly inhibited ESCC invasion and metastasis in vitro. Consistently, a xenograft assay showed that knockdown of USP18 in ESCC cell suppressed their dissemination to lung tissue in vivo. Furthermore, we showed that USP18 promoted ESCC cell metastasis by inducing ZEB1 mediated epithelial-mesenchymal transition (EMT). Importantly, our results demonstrated that the oncogenic effect of USP18 in ESCC is partially dependent on ZEB1 enhancement. Mechanistic investigations revealed that USP18 directly bound ZEB1 and decreased its ubiquitination to enhance the protein stability of ZEB1 in ESCC cells. Overall, our data highlighted an essential role of USP18 in ESCC metastasis, suggesting that it could be a potential diagnostic and therapeutic target for ESCC.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Ice Recrystallization Inhibition Activity of Soy Protein Hydrolysates

Identifying and developing ice recrystallization inhibitors from sustainable food proteins such as soy protein isolate (SPI) can lead to practical applications in both pharmaceutical and food industries. Here, the objective of this study was to investigate the ice recrystallization inhibition (IRI) activity of SPI hydrolysates, and this was achieved by using an IRI activity-guided fractionation approach and relating IRI activity to interfacial molecular activity measured by vibrational sum frequency generation (VSFG). In addition, the impact of molecular weight (MW) and enzyme specificity was analyzed using three different proteases (Alcalase, trypsin, and pancreatin) and varying hydrolysis times. Using preparative chromatography, hydrolysates from each enzyme treatment were fractionated into five different MW fractions (F1–F5), which were then characterized by high-performance liquid chromatography (HPLC). All SPI hydrolysates had IRI activity, resulting in a 57–29% ice crystal diameter reduction when compared to native SPI. The F1 fraction (of 4–14 kDa) was most effective among all tested hydrolysates, while the lower MW peptide fractions lacked activity. One sample (SPI-ALC 20-F1) had a 52% reduction of ice crystal size at a lower concentration of 2% compared to the typical 4% used. SFG showed a difference in H-bonding and hydrophobic interactions of the molecules on the water/air interface, which may be linked to IRI activity. This study demonstrates for the first time the ability of SPI hydrolysates to inhibit ice crystal growth and the potential application of SFG to study molecular interaction at the interface that may help illustrate the mechanism of action.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

tinyIFD: A High-Throughput Binding Pose Refinement Workflow Through Induced-Fit Ligand Docking

A critical step in structure-based drug discovery is predicting whether and how a candidate molecule binds to a model of a therapeutic target. However, substantial protein side chain movements prevent current screening methods, such as docking, from accurately predicting the ligand conformations and require expensive refinements to produce viable candidates. Here, we present the development of a high-throughput and flexible ligand pose refinement workflow, called “tinyIFD”. The main features of the workflow include the use of specialized high-throughput, small-system MD simulation code mdgx.cuda and an actively learning model zoo approach. We show the application of this workflow on a large test set of diverse protein targets, achieving 66% and 76% success rates for finding a crystal-like pose within the top-2 and top-5 poses, respectively. We also applied this workflow to the SARS-CoV-2 main protease (M pro ) inhibitors, where we demonstrate the benefit of the active learning aspect in this workflow.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

3D-Scaffold: A Deep Learning Framework to Generate 3D Coordinates of Drug-like Molecules with Desired Scaffolds

The prerequisite of therapeutic drug design is to identify novel molecules with desired biophysical and biochemical properties. Deep generative models have demonstrated their ability to find such molecules by exploring a huge chemical space efficiently. An effective way to obtain molecules with desired target properties is the preservation of critical scaffolds in the generation process. To this end, we propose a domain aware generative framework called 3D-Scaffold that takes 3D coordinates of a desired scaffold as an input and generates 3D coordinates of novel therapeutic candidates as an output while always preserving the desired scaffolds in generated structures. We show that our framework generates predominantly valid, unique, novel, and experimentally synthesizable molecules that have drug-like properties similar to the molecules in the training set. Using domain specific datasets, we generate covalent and non-covalent antiviral inhibitors. Therefore, to measure the success of our framework in generating therapeutic candidates, generated structures were subjected to high throughput virtual screening via docking simulations, which shows favorable interaction against SARS-CoV-2 main protease and non-structural protein endoribonuclease (NSP15) targets. Most importantly, our model performs well with relatively small volumes of training data and generalizes to new scaffolds, making it applicable to other domain.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

DNA-PAINT Imaging with Hydrogel Imprinting and Clearing

Hydrogel-embedding is a versatile technique in fluorescence microscopy, offering stabilization, optical clearing, and the physical expansion of biological specimens. DNA-PAINT is a super-resolution microscopy approach based on the diffusion and transient binding of fluorescently labeled oligos, but its feasibility in hydrogels has not yet been explored. In this study, we demonstrate that polyacrylamide hydrogels support sufficient diffusion for effective DNA-PAINT imaging. Using acrydite-anchored oligonucleotides imprinted from patterned DNA origami nanostructures and microtubule filaments in fixed cells, we find that hydrogel embedding preserves docking strand positioning at the nanoscale. Sample clearing via protease treatment had minor structural effects on the microtubule structure and enhanced diffusion and accessibility to hydrogel-imprinted docking strands. Our work demonstrates promising potential for diffusion and binding-based fluorescence imaging applications in hydrogel-embedded samples.

DNA origami↗
DOE OSTI2020

Structural plasticity of SARS-CoV-2 3CL Mpro active site cavity revealed by room temperature X-ray crystallography

The COVID-19 disease caused by the SARS-CoV-2 coronavirus has become a pandemic health crisis. An attractive target for antiviral inhibitors is the main protease 3CL Mpro due to its essential role in processing the polyproteins translated from viral RNA. Here we report the room temperature X-ray structure of unliganded SARS-CoV-2 3CL Mpro, revealing the ligand-free structure of the active site and the conformation of the catalytic site cavity at near-physiological temperature. Comparison with previously reported low-temperature ligand-free and inhibitor-bound structures suggest that the room temperature structure may provide more relevant information at physiological temperatures for aiding in molecular docking studies.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Self-assembly and regulation of protein cages from pre-organised coiled-coil modules

Coiled-coil protein origami (CCPO) is a modular strategy for the de novo design of polypeptide nanostructures. CCPO folds are defined by the sequential order of concatenated orthogonal coiled-coil (CC) dimer-forming peptides, where a single-chain protein is programmed to fold into a polyhedral cage. Self-assembly of CC-based nanostructures from several chains, similarly as in DNA nanotechnology, could facilitate the design of more complex assemblies and the introduction of functionalities. Here, we show the design of a de novo triangular bipyramid fold comprising 18 CC-forming segments and define the strategy for the two-chain self-assembly of the bipyramidal cage from asymmetric and pseudo-symmetric pre-organised structural modules. In addition, by introducing a protease cleavage site and masking the interfacial CC-forming segments in the two-chain bipyramidal cage, we devise a proteolysis-mediated conformational switch. This strategy could be extended to other modular protein folds, facilitating the construction of dynamic multi-chain CC-based complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Tunable, biodegradable grafting-from glycopolypeptide bottlebrush polymers

The cellular glycocalyx and extracellular matrix are rich in glycoproteins and proteoglycans that play essential physical and biochemical roles in all life. Synthetic mimics of these natural bottlebrush polymers have wide applications in biomedicine, yet preparation has been challenged by their high grafting and glycosylation densities. Using one-pot dual-catalysis polymerization of glycan-bearing α-amino acid N-carboxyanhydrides, we report grafting-from glycopolypeptide brushes. The materials are chemically and conformationally tunable where backbone and sidechain lengths were precisely altered, grafting density modulated up to 100%, and glycan density and identity tuned by monomer feed ratios. The glycobrushes are composed entirely of sugars and amino acids, are non-toxic to cells, and are degradable by natural proteases. Inspired by native lipid-anchored proteoglycans, cholesterol-modified glycobrushes were displayed on the surface of live human cells. Our materials overcome long-standing challenges in glycobrush polymer synthesis and offer new opportunities to examine glycan presentation and multivalency from chemically defined scaffolds.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Structural and functional characterization of NEMO cleavage by SARS-CoV-2 3CLpro

Abstract In addition to its essential role in viral polyprotein processing, the SARS-CoV-2 3C-like protease (3CLpro) can cleave human immune signaling proteins, like NF-κB Essential Modulator (NEMO) and deregulate the host immune response. Here, in vitro assays show that SARS-CoV-2 3CLpro cleaves NEMO with fine-tuned efficiency. Analysis of the 2.50 Å resolution crystal structure of 3CLpro C145S bound to NEMO 226–234 reveals subsites that tolerate a range of viral and host substrates through main chain hydrogen bonds while also enforcing specificity using side chain hydrogen bonds and hydrophobic contacts. Machine learning- and physics-based computational methods predict that variation in key binding residues of 3CLpro-NEMO helps explain the high fitness of SARS-CoV-2 in humans. We posit that cleavage of NEMO is an important piece of information to be accounted for, in the pathology of COVID-19.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

Structural determinants for pH-dependent activation of a plant metacaspase

Arabidopsis thaliana metacaspase 9 (AtMC9) plays roles in clearing dead cells, forming xylem vessels, and regulating immunity and programmed cell death in plants. The protease's activation is controlled by pH levels, but the exact structural mechanism behind this has not been elucidated. In this work, high-resolution crystal structures for AtMC9 at active (pH 5.5 and pH 4.2) and inactive (pH 7.5) conditions are reported. The three structures are similar except for local conformations where their hydrogen bonding interactions with solvents are mediated through the protonation of specific titratable amino acid residues' side chains. By combining structural analysis, molecular dynamics simulations under constant pHs, and biochemical assays coupled with site-directed mutagenesis, we show that the regulation of AtMC9 activation involves multiple titratable glutamate and histidine residues across the three domains of p20, linker, and p10. Specifically, deprotonated Glu112, His193, and His208 can suppress AtMC9 proteolytic activity, while protonation of Glu255 and His307 at acidic pH may promote it. This study provides valuable insights into the pH-dependent activation of AtMC9 and could potentially lead to improving crops with enhanced immunity and controlled cell death, ultimately increasing agricultural productivity.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Transforming an ATP-dependent enzyme into a dissipative, self-assembling system

Nucleoside triphosphate (NTP)-dependent protein assemblies such as microtubules and actin filaments have inspired the development of diverse chemically fueled molecular machines and active materials but their functional sophistication has yet to be matched by design. Given this challenge, we asked whether it is possible to transform a natural adenosine 5'-triphosphate (ATP)-dependent enzyme into a dissipative self-assembling system, thereby altering the structural and functional mode in which chemical energy is used. Furthermore we report that FtsH (filamentous temperature-sensitive protease H), a hexameric ATPase involved in membrane protein degradation, can be readily engineered to form one-dimensional helical nanotubes. FtsH nanotubes require constant energy input to maintain their integrity and degrade over time with the concomitant hydrolysis of ATP, analogous to natural NTP-dependent cytoskeletal assemblies. Yet, in contrast to natural dissipative systems, ATP hydrolysis is catalyzed by free FtsH protomers and FtsH nanotubes serve to conserve ATP, leading to transient assemblies whose lifetimes can be tuned from days to minutes through the inclusion of external ATPases in solution.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Enhanced purification coupled with biophysical analyses shows cross-β structure as a core building block for Streptococcus mutans functional amyloids

Streptococcus mutans is an etiologic agent of human dental caries that forms dental plaque biofilms containing functional amyloids. Three amyloidogenic proteins, P1, WapA, and Smu_63c were previously identified. C123 and AgA are naturally occurring amyloid-forming fragments of P1 and WapA, respectively. We determined that four amyloidophilic dyes, ThT, CDy11, BD-oligo, and MK-H4, differentiate C123, AgA, and Smu_63c amyloid from monomers, but non-specific binding to bacterial cells in the absence of amyloid precludes their utility for identifying amyloid in biofilms. Congo redinduced birefringence is a more specific indicator of amyloid formation and differentiates biofilms formed by wild-type S. mutans from a triple ΔP1/WapA/Smu_63c mutant with reduced bioiflm forming capabilities. Amyloid accumulation is a late event, appearing in older S. mutans biofilms after 60hours of growth. Amyloid derived from pure preparations of all three proteins is visualized by electron microscopy as mat-like structures. Typical amyloid fibers become evident following protease digestion to eliminate non-specific aggregates and monomers. Amyloid mats, similar in appearance to those reported in S. mutans biofilm extracellular matrices, are reconstituted by co-incubation of monomers and amyloid fibers. X-ray fiber diffraction of amyloid mats and fibers from all three proteins demonstrate patterns reflective of a cross-β amyloid structure.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

An alternative domain-swapped structure of the Pyrococcus horikoshii PolII mini-intein

Protein splicing is a post-translational process by which an intein catalyzes its own excision from flanking polypeptides, or exteins, concomitant with extein ligation. Many inteins have nested homing endonuclease domains that facilitate their propagation into intein-less alleles, whereas other inteins lack the homing endonuclease (HEN) and are called mini-inteins. The mini-intein that interrupts the DNA PolII of Pyrococcus horikoshii has a linker region in place of the HEN domain that is shorter than the linker in a closely related intein from Pyrococcus abyssi. The P. horikoshii PolII intein requires a higher temperature for catalytic activity and is more stable to digestion by the thermostable protease thermolysin, suggesting that it is more rigid than the P. abyssi intein. We solved a crystal structure of the intein precursor that revealed a domain-swapped dimer. Inteins found as domain swapped dimers have been shown to promote intein-mediated protein alternative splicing, but the solved P. horikoshii PolII intein structure has an active site unlikely to be catalytically competent.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

A substrate-induced gating mechanism is conserved among Gram-positive IgA1 metalloproteases

The mucosal adaptive immune response is dependent on the production of IgA antibodies and particularly IgA1, yet opportunistic bacteria have evolved mechanisms to specifically block this response by producing IgA1 proteases (IgA1Ps). Our lab was the first to describe the structures of a metal-dependent IgA1P (metallo-IgA1P) produced from Gram-positive Streptococcus pneumoniae both in the absence and presence of its IgA1 substrate through cryo-EM single particle reconstructions. This prior study revealed an active-site gating mechanism reliant on substrate-induced conformational changes to the enzyme that begged the question of whether such a mechanism is conserved among the wider Gram-positive metallo-IgA1P subfamily of virulence factors. Here, we used cryo-EM to characterize the metallo-IgA1P of a more distantly related family member from Gemella haemolysans, an emerging opportunistic pathogen implicated in meningitis, endocarditis, and more recently bacteremia in the elderly. While the substrate-free structures of these two metallo-IgA1Ps exhibit differences in the relative starting positions of the domain responsible for gating substrate, the enzymes have similar domain orientations when bound to IgA1. Together with biochemical studies that indicate these metallo-IgA1Ps have similar binding affinities and activities, these data indicate that metallo-IgA1P binding requires the specific IgA1 substrate to open the enzymes for access to their active site and thus, largely conform to an “induced fit” model.

59 BASIC BIOLOGICAL SCIENCES↗