Biology subjects

Joachimiak, A.

Publications and source records attributed to Joachimiak, A..

16 recordsLinked to original sources

bioRxiv2026

Cryo-EM structure of detergent-bound Vibrio cholerae MakA captures a candidate intermediate between the soluble form and mature assembly of an α-pore-forming toxin

The tripartite toxin MakA/MakB/MakE from Vibrio cholerae belongs to a family of -pore-forming toxins that undergo extensive conformational rearrangements upon interacting with membrane. While soluble structures of MakA, MakB and MakE have been determined, the structural basis of membrane association and pore assembly remains poorly understood. Here, we report a cryo-electron microscopy structure of a detergent-associated form of MakA at a global resolution of 3.13 Angstrom, with focused refinement of a flexible region improving the local resolution to 2.68 Angstrom. This structure consists of a trimer of MakA asymmetric homodimers, in which each subunit adopts a transmembrane -helical conformation distinct from the previously reported soluble structure. The asymmetric homodimer closely resembles the building block observed in the previously reported helical MakA assembly and is structurally similar to the homodimeric building blocks of the Aeromonas hydrophila AhlB and Serratia marcescens SmhA pores, and the heterodimeric building blocks of the Xenorhabdus nematophila XaxAB and Yersinia enterocolitica YaxAB pores, suggesting a conserved assembly principle among distantly related -pore-forming toxins. Complementary hydropathy analysis, AlphaFold2 modeling, and liposome-based assays reveal distinct roles for the three components, with MakA acting as the primary membrane-inserting subunit, MakE exhibiting low but consistent membrane-association, and MakB alone remaining largely soluble. Together, these results support a model in which the MakA asymmetric homodimer represents a plausible early membrane-insertion unit and building block for pore assembly, while the trimer of dimers represents an early assembly intermediate.

microbiology↗

bioRxiv2026

Phylogenetic Analysis and Structural Evaluation of Staphylococcus aureus Serine-Aspartate Repeat-Containing Protein D with a Focus on Periprosthetic Joint Infection

Serine-aspartate repeat-containing protein D (SdrD) is a Staphylococcus aureus cell wall-anchored, calcium-binding adhesin member of the MSCRAMM Sdr subfamily that may contribute to bacterial adhesion and virulence. S. aureus is the most common cause of periprosthetic joint infection (PJI). Population-level distribution and sequence diversity of SdrD among clinical PJI isolates have not been systematically characterized, and the SdrD binding mechanism is still not well understood. To address these gaps, sdrD alleles were queried across 156 newly sequenced PJI isolates and compared to publicly available S. aureus genomes, and nucleotide- and protein-level phylogenies of the sdrCDE locus constructed. The SdrD crystal structure from S. aureus JH1 was determined, with solution small-angle X-ray scattering (SAXS) and molecular dynamics (MD) simulations, and assessment of conformational changes with calcium depletion. Three dominant sdrD subtypes were defined, associating with USA300, JH1, and TCH60; the JH1 sdrD subtype was predominant among PJI isolates. Structural studies showed that the conformation of individual domains and interdomain organization of the multidomain SdrD have limited flexibility in solution, and that the calcium-binding B domain retains its core fold under conditions of calcium depletion. Together, the findings presented support functional diversification among Sdr family members in mediating host attachment and inform a re-evaluation of the ligand-binding mechanism previously proposed for SdrD. AUTHOR SUMMARYStaphylococcus aureus is the leading cause of infections that develop around joint implants (periprosthetic joint infection, PJI). This bacterium has a large arsenal of surface proteins that allow it to stick to human tissues and implanted devices. This work focused on one such protein, SdrD, which has been linked to implant-associated infections but the structure and diversity of which among patients with PJI had not been well characterized. The genetic sequences of SdrD were analyzed across thousands of bacterial genomes, including those from patients with PJI. Distinct genetic variants of the protein were found, one of which was particularly common with PJI. The three-dimensional structure of SdrD was determined at atomic resolution and solution small-angle X-ray scattering (SAXS) and molecular dynamics used to study how it moves and responds to changes in its environment. Contrary to what was previously described, SdrD was shown to be relatively rigid. These findings change how SdrDs mechanism of action should be considered, potentially informing design strategies to block bacterial attachment before infection takes hold.

biophysics↗

bioRxiv2025

PANCS-spec-Binders: A system for rapidly discovering isoform- or epitope-specific binders

Proteins that bind to a target protein of interest, termed "binders," are essential components of biological research reagents and therapeutics. Target proteins present multiple binding surfaces with varying interaction potential. High-potential surfaces, or "hot spots," are experimentally identified as the most probable binding sites in de novo discovery campaigns. However, hot spots and their default binding modes do not always confer the desired specificity. Related proteins or isoforms often share similar hot spots, resulting in promiscuous binding. Interaction with a hot spot may also fail to elicit the intended biological outcome. Consequently, methods that direct de novo binder discovery toward targets with defined specificity are critically needed. We recently developed phage-assisted non-continuous selection of binders (PANCS-Binders), a selection platform with unparalleled speed and sequence-function fidelity that enables routine de novo binder discovery within days. However, because PANCS-Binder selections enrich variants based primarily on affinity, secondary screening is unlikely to identify binders to lesser hot spots because of the high likelihood of convergence. These alternative binding surfaces with weaker inherent interactions may possess desirable specificity profiles. Here, we develop PANCS-spec-Binders, which incorporates simultaneous selection and counterselection to control the specificity of enriched binders. We demonstrate PANCS-spec-Binders in two proof- of-concept applications: (1) discovery of isoform-selective binders that bind HRAS with >100-fold higher affinity than the highly related KRAS isoform, and (2) discovery of epitope-specific binders that either target or avoid the LIR interaction region of LC3B. PANCS-spec-Binders enables rapid identification of binders with defined specificity within days. SIGNIFICANCEAffinity reagents, termed "binders", are essential tools in research and therapeutic development. Binders generally require high specificity either at the selectivity level (binding only the target protein, but not related proteins) or at the epitope level (binding only at a specific surface on the target rather than another). While methods to discover binders in general have progressed, identifying binders with defined specificity features often requires extensive secondary screening and frequently results in failure. Here, we adapt our recently developed binder discovery platform to solve these two selectivity problems. By rapidly screening billions of variants, we can direct specificity between highly related proteins, direct binding to a specific epitope, and, because of the fidelity of our selections, identify binders that specifically avoid a defined epitope.

synthetic biology↗

bioRxiv2025

A funnel approach to enable analyses of epitope-specific human CD4 T cells specific for influenza and SARS-CoV-2.

Protection from pathogenic organisms relies heavily on the adaptive immune response, for which key regulators are CD4 T cells. CD4 T cells, notable in the complexity of their repertoire and functional potential, can most easily be dissected with the ability to identify, quantify, characterize and isolate epitope-specific cells. In the study reported here, we present a systematic and unbiassed strategy that has enabled identification of highly immunogenic peptide epitopes derived from influenza virus and SARS-CoV-2, presented by human HLA-DR proteins. Coupling the use of HLA-DR transgenic mice with infection and vaccination with highly sensitive epitope specific cytokine ELISpot assays, we have narrowed the potential epitopes from 450-600 peptides to 5-15 peptides, by an iterative process of elimination and selection which we have termed a funnel approach. These epitopes have been validated in HLA-DR typed human CD4 T cells directly ex vivo and enabled derivation and implementation of HLA-DR peptide tetramers. Tetramer staining of human PBMCs enriched CD4 T memory populations from healthy adult subjects highlighting this approach as a sensitive and specific method of identifying novel epitopes and subsequent CD4 T cell responses to human viral infections. ImportanceTracking single epitope-specific CD4 T cells enables sophisticated analyses of the human response to infectious pathogens, vaccines and probing the human CD4 T cell immune memory compartment. The studies presented here provide a unbiased strategy for accomplishing this goal and provide a verified compilation of candidate HLA-DR restricted CD4 T cell peptide epitopes for future studies by researchers in the field of human immunology.

immunology↗

bioRxiv2023

Molecular basis for dual functions in pilus assembly modulated by the lid of a pilus-specific sortase

The biphasic assembly of Gram-positive pili begins with the covalent polymerization of distinct pilins catalyzed by a pilus-specific sortase, followed by the cell wall anchoring of the resulting polymers mediated by the housekeeping sortase. In Actinomyces oris, the pilus-specific sortase SrtC2 not only polymerizes FimA pilins to assemble type 2 fimbriae with CafA at the tip, but it can also act as the anchoring sortase, linking both FimA polymers and SrtC1-catalyzed FimP polymers (type 1 fimbriae) to peptidoglycan when the housekeeping sortase SrtA is inactive. To date, the structure-function determinants governing the unique substrate specificity and dual enzymatic activity of SrtC2 have not been illuminated. Here, we present the crystal structure of SrtC2 solved to 2.10-[A] resolution. SrtC2 harbors a canonical sortase fold and a lid typical for class C sortases and additional features specific to SrtC2. Structural, biochemical, and mutational analyses of SrtC2 reveal that the extended lid of SrtC2 modulates its dual activity. Specifically, we demonstrate that the polymerizing activity of SrtC2 is still maintained by alanine-substitution, partial deletion, and replacement of the SrtC2 lid with the SrtC1 lid. Strikingly, pilus incorporation of CafA is significantly reduced by these mutations, leading to compromised polymicrobial interactions mediated by CafA. In a srtA mutant, the partial deletion of the SrtC2 lid reduces surface anchoring of FimP polymers, and the lid-swapping mutation enhances this process, while both mutations diminish surface anchoring of FimA pili. Evidently, the extended lid of SrtC2 enables the enzyme the cell wall-anchoring activity in a substrate-selective fashion.

microbiology↗

bioRxiv2022

New system for serial crystallography data collection at SBC APS

Serial synchrotron crystallography enables studies of protein structures under physiological temperature and reduced radiation damage by collection of data from thousands of crystals. The Structural Biology Center at Sector 19 of the Advanced Photon Source has implemented a fixed-target approach with a new 3D printed mesh-holder optimized for sample handling. The holder immobilizes a crystal suspension or droplet emulsion on a nylon mesh, trapping and sealing a near-monolayer of crystals in its mother liquor between two thin mylar films. Data can be rapidly collected in scan mode and analyzed in near real-time using piezoelectric linear stages assembled in an XYZ arrangement, controlled with a graphical user interface and analyzed by using a high-performance computing pipeline. Here, the system was applied to two {beta}-lactamases: a class D serine {beta}-lactamase from Chitinophaga pinensis DSM 2588 and L1 metallo-{beta} -lactamase from Stenotrophomonas maltophilia K279a.

molecular biology↗

bioRxiv2021

Dual domain recognition determines SARS-CoV-2 PLpro selectivity for human ISG15 and K48-linked di-ubiquitin

The Papain-like protease (PLpro) is a domain of a multi-functional, non-structural protein 3 of coronaviruses. PLpro cleaves viral polyproteins and posttranslational conjugates with poly-ubiquitin and protective ISG15, composed of two ubiquitin-like (UBL) domains. Across coronaviruses, PLpro showed divergent selectivity for recognition and cleavage of posttranslational conjugates despite sequence conservation. We show that SARS-CoV-2 PLpro binds human ISG15 and K48-linked di-ubiquitin (K48-Ub2) with nanomolar affinity and detect alternate weaker-binding modes. Crystal structures of untethered PLpro complexes with ISG15 and K48-Ub2 combined with solution NMR and cross-linking mass spectrometry revealed how the two domains of ISG15 or K48-Ub2 are differently utilized in interactions with PLpro. Analysis of protein interface energetics predicted differential binding stabilities of the two UBL/Ub domains that were validated experimentally. We emphasize how substrate recognition can be tuned to cleave specifically ISG15 or K48-Ub2 modifications while retaining capacity to cleave mono-Ub conjugates. These results highlight alternative druggable surfaces that would inhibit PLpro function.

biophysics↗

bioRxiv2020

SARS-CoV-2 infection severity is linked to superior humoral immunity against the spike

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is currently causing a global pandemic. The antigen specificity and kinetics of the antibody response mounted against this novel virus are not understood in detail. Here, we report that subjects with a more severe SARS-CoV-2 infection exhibit a larger antibody response against the spike and nucleocapsid protein and epitope spreading to subdominant viral antigens, such as open reading frame 8 and non-structural proteins. Subjects with a greater antibody response mounted a larger memory B cell response against the spike, but not the nucleocapsid protein. Additionally, we revealed that antibodies against the spike are still capable of binding the D614G spike mutant and cross-react with the SARS-CoV-1 receptor binding domain. Together, this study reveals that subjects with a more severe SARS-CoV-2 infection exhibit a greater overall antibody response to the spike and nucleocapsid protein and a larger memory B cell response against the spike.

immunology↗

bioRxiv2020

Methylation of RNA Cap in SARS-CoV-2 captured by serial crystallography

The genome of the SARS-CoV-2 coronavirus contains 29 proteins, of which 15 are nonstructural. Nsp10 and Nsp16 form a complex responsible for the capping of mRNA at the 5' terminus. In the methylation reaction the S-adenosyl-L-methionine serves as the donor of the methyl group that is transferred to Cap-0 at the first transcribed nucleotide to create Cap-1. The presence of Cap-1 makes viral RNAs mimic the host transcripts and prevents their degradation. To investigate the 2'-O methyltransferase activity of SARS-CoV-2 Nsp10/16, we applied fixed-target serial synchrotron crystallography (SSX) which allows for physiological temperature data collection from thousands of crystals, significantly reducing the x-ray dose while maintaining a biologically relevant temperature. We determined crystal structures of Nsp10/16 that revealed the states before and after the methylation reaction, for the first time illustrating coronavirus Nsp10/16 complexes with the m7GpppAm2'-O Cap-1, where 2'OH of ribose is methylated. We compare these structures with structures of Nsp10/16 at 297 K and 100 K collected from a single crystal. This data provide important mechanistic insight and can be used to design small molecules that inhibit viral RNA maturation making SARS-CoV-2 sensitive to host innate response.

molecular biology↗

bioRxiv2020

Structure of papain-like protease from SARS-CoV-2 and its complexes with non-covalent inhibitors

The number of new cases world-wide for the COVID-19 disease is increasing dramatically, while efforts to contain Severe Acute Respiratory Syndrome Coronavirus 2 is producing varied results in different countries. There are three key SARS-CoV-2 enzymes potentially targetable with antivirals: papain-like protease (PLpro), main protease (Mpro), and RNA-dependent RNA polymerase. Of these, PLpro is an especially attractive target because it plays an essential role in several viral replication processes, including cleavage and maturation of viral polyproteins, assembly of the replicase-transcriptase complex (RTC), and disruption of host viral response machinery to facilitate viral proliferation and replication. Moreover, this enzyme is conserved across different coronaviruses and promising inhibitors have already been discovered for its SARS-CoV variant. Here we report a substantive body of structural, biochemical, and virus replication studies that identify several inhibitors of the enzyme from SARS-CoV-2 in both wild-type and mutant forms. These efforts include the first structures of wild-type PLpro, the active site C111S mutant, and their complexes with inhibitors, determined at 1.60-2.70 Angstroms. This collection of structures provides fundamental molecular and mechanistic insight to PLpro, and critically, illustrates details for inhibitors recognition and interactions. All presented compounds inhibit the peptidase activity of PLpro in vitro, and some molecules block SARS-CoV-2 replication in cell culture assays. These collated findings will accelerate further structure-based drug design efforts targeting PLpro, with the ultimate goal of identifying high-affinity inhibitors of clinical value for SARS-CoV-2.

molecular biology↗

bioRxiv2020

Tipiracil binds to uridine site and inhibits Nsp15 endoribonuclease NendoU from SARS-CoV-2

ABSTRACTSARS-CoV-2 Nsp15 is a uridylate-specific endoribonuclease with C-terminal catalytic domain belonging to the EndoU family. It degrades the polyuridine extensions in (-) sense strand of viral RNA and some non-translated RNA on (+) sense strand. This activity seems to be responsible for the interference with the innate immune response and evasion of host pattern recognition. Nsp15 is highly conserved in coronaviruses suggesting that its activity is important for virus replication. Here we report first structures with bound nucleotides and show that SARS-CoV-2 Nsp15 specifically recognizes U in a pattern previously predicted for EndoU. In the presence of manganese ions, the enzyme cleaves unpaired RNAs. Inhibitors of Nsp15 have been reported but not actively pursued into therapeutics. The current COVID-19 pandemic brought to attention the repurposing of existing drugs and the rapid identification of new antiviral compounds. Tipiracil is an FDA approved drug that is used with trifluridine in the treatment of colorectal cancer. Here, we combine crystallography, biochemical and whole cell assays, and show that this compound inhibits SARS-CoV-2 Nsp15 and interacts with the uridine binding pocket of the enzyme’s active site, providing basis for the uracil scaffold-based drug development.Competing Interest StatementThe authors have declared no competing interest.View Full Text

molecular biology↗

bioRxiv2020

Crystal structures of SARS-CoV-2 ADP-ribose phosphatase (ADRP): from the apo form to ligand complexes

Among 15 nonstructural proteins (Nsps), the newly emerging SARS-CoV-2 encodes a large, multidomain Nsp3. One of its units is ADP-ribose phosphatase domain (ADRP, also known as macrodomain) which is believed to interfere with the host immune response. Such a function appears to be linked to the proteins ability to remove ADP-ribose from ADP-ribosylated proteins and RNA, yet the precise role and molecular targets of the enzyme remains unknown. Here, we have determined five, high resolution (1.07 - 2.01 [A]) crystal structures corresponding to the apo form of the protein and complexes with 2-(N-morpholino)ethanesulfonic acid (MES), AMP and ADPr. We show that the protein undergoes conformational changes to adapt to the ligand in a manner previously observed before for in close homologs from other viruses. We also identify a conserved water molecule that may participate in hydrolysis. This work builds foundations for future structure-based research of the ADRP, including search for potential antiviral therapeutics.

molecular biology↗

bioRxiv2020

The crystal structure of nsp10-nsp16 heterodimer from SARS CoV-2in complex with S-adenosylmethionine

SARS-CoV-2 is a member of the coronaviridae family and is the etiological agent of the respiratory Coronavirus Disease 2019. The virus has spread rapidly around the world resulting in over two million cases and nearly 150,000 deaths as of April 17, 2020. Since no treatments or vaccines are available to treat COVID-19 and SARS-CoV-2, respiratory complications derived from the infections have overwhelmed healthcare systems around the world. This virus is related to SARS-CoV-1, the virus that caused the 2002-2004 outbreak of Severe Acute Respiratory Syndrome. In January 2020, the Center for Structural Genomics of Infectious Diseases implemented a structural genomics pipeline to solve the structures of proteins essential for coronavirus replication-transcription. Here we show the first structure of the SARS-CoV-2 nsp10-nsp16 2-O-methyltransferase complex with S-adenosylmethionine at a resolution of 1.80 [A]. This heterodimer complex is essential for capping viral mRNA transcripts for efficient translation and to evade immune surveillance.

biochemistry↗

bioRxiv2020

Therapeutic genetic variation revealed in diverse Hsp104 homologs

The AAA+ protein disaggregase, Hsp104, increases fitness under stress by reversing stress-induced protein aggregation. We have engineered potentiated Hsp104 variants to antagonize proteotoxic misfolding linked to human neurodegenerative diseases. However, these Hsp104 variants can exhibit off-target toxicity, which may limit their therapeutic utility. Hsp104 is conserved among all nonmetazoan eukaryotes, which raises the possibility that natural variants might exist with enhanced, selective activity against neurodegenerative disease substrates. To assess this possibility, we screened a cross-kingdom collection of Hsp104 homologs in several yeast proteotoxicity models. We uncovered therapeutic genetic variation among several Hsp104 homologs that specifically antagonize TDP-43 or -synuclein condensate formation and toxicity in yeast, human cells, and C. elegans. Surprisingly, this variation manifested as increased passive chaperone activity, distinct from disaggregase activity, which neutralizes proteotoxicity of specific substrates. Thus, by exploring natural tuning of passive chaperone activity we elucidated enhanced, substrate-specific agents to counter proteotoxicity underlying neurodegenerative disease.

biochemistry↗

bioRxiv2020

Crystal structure of Nsp15 endoribonuclease NendoU from SARS-CoV-2

Severe Acute Respiratory Syndrome Coronavirus 2 is rapidly spreading around the world. There is no existing vaccine or proven drug to prevent infections and stop virus proliferation. Although this virus is similar to human and animal SARS- and MERS-CoVs the detailed information about SARS-CoV-2 proteins structures and functions is urgently needed to rapidly develop effective vaccines, antibodies and antivirals. We applied high-throughput protein production and structure determination pipeline at the Center for Structural Genomics of Infectious Diseases to produce SARS-CoV-2 proteins and structures. Here we report the high-resolution crystal structure of endoribonuclease Nsp15/NendoU from SARS-CoV-2 - a virus causing current world-wide epidemics. We compare this structure with previously reported models of Nsp15 from SARS and MERS coronaviruses.

molecular biology↗

bioRxiv2019

A 2.08 A resolution structure of HLB5, a novel cellulase from the anaerobic gut bacterium Parabacteroides johnsonii DSM 18315.

Cellulases play a significant role in the degradation of complex carbohydrates. In the human gut anaerobic bacteria are essential to the well-being of the host by producing these essential enzymes that convert plant polymers into simple sugars that can then be further metabolized by the host. Here we report the 2.08 [A] resolution structure of HLB5, a chemically verified cellulase that was identified previously from an anaerobic gut bacterium and that has no structural cellulase homologues in PDB nor possesses any conserved region typical for enzymes that degrade carbohydrates. We anticipate that the information presented here will facilitate the identification of additional cellulases for which no homologues have been identified until to date and in enhancing our understanding how these novel cellulases bind and hydrolyze their substrates.

systems biology↗