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Smith CA, Sonneson GJ, Hoey RJ, Hinerman JM, Sheehy K, Walter R, Herr AB, Horn JR. Molecular recognition requires dimerization of a VHH antibody. MAbs 2023; 15:2215363. [PMID: 37243579 PMCID: PMC10228392 DOI: 10.1080/19420862.2023.2215363] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Revised: 05/02/2023] [Accepted: 05/15/2023] [Indexed: 05/29/2023] Open
Abstract
Camelid heavy-chain-only antibodies are a unique class of antibody that possesses only a single variable domain (termed VHH) for antigen recognition. Despite their apparent canonical mechanism of target recognition, where a single VHH domain binds a single target, an anti-caffeine VHH has been observed to possess 2:1 stoichiometry. Here, the structure of the anti-caffeine VHH/caffeine complex enabled the generation and biophysical analysis of variants that were used to better understand the role of VHH homodimerization in caffeine recognition. VHH interface mutants and caffeine analogs, which were examined to probe the mechanism of caffeine binding, suggested caffeine recognition is only possible with the VHH dimer species. Correspondingly, in the absence of caffeine, the anti-caffeine VHH was found to form a dimer with a dimerization constant comparable to that observed with VH:VL domains in conventional antibody systems, which was most stable near physiological temperature. While the VHH:VHH dimer structure (at 1.13 Å resolution) is reminiscent of conventional VH:VL heterodimers, the homodimeric VHH possesses a smaller angle of domain interaction, as well as a larger amount of apolar surface area burial. To test the general hypothesis that the short complementarity-determining region-3 (CDR3) may help drive VHH:VHH homodimerization, an anti-picloram VHH domain containing a short CDR3 was generated and characterized, which revealed it also existed as dimer species in solution. These results suggest homodimer-driven recognition may represent a more common method of VHH ligand recognition, opening opportunities for novel VHH homodimer affinity reagents and helping to guide their use in chemically induced dimerization applications.
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Affiliation(s)
- Christopher A. Smith
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, USA
| | - Gregory J. Sonneson
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, USA
| | - Robert J. Hoey
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, USA
| | - Jennifer M. Hinerman
- Division of Immunobiology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH USA
| | - Kimberly Sheehy
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, USA
| | - Richard Walter
- Shamrock Structures, LLC, Woodridge, IL, USA
- Joliet XTALPAC LLC, USA
| | - Andrew B. Herr
- Division of Immunobiology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH USA
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH USA
| | - James R. Horn
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, USA
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Yarawsky AE, Hopkins JB, Chatzimagas L, Hub JS, Herr AB. Solution Structural Studies of Pre-amyloid Oligomer States of the Biofilm Protein Aap. J Mol Biol 2022; 434:167708. [PMID: 35777467 PMCID: PMC9615840 DOI: 10.1016/j.jmb.2022.167708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Revised: 06/20/2022] [Accepted: 06/25/2022] [Indexed: 11/16/2022]
Abstract
Staphylococcus epidermidis is a commensal bacterium on human skin that is also the leading cause of medical device-related infections. The accumulation-associated protein (Aap) from S. epidermidis is a critical factor for infection via its ability to mediate biofilm formation. The B-repeat superdomain of Aap is composed of 5 to 17 Zn2+-binding B-repeats, which undergo rapid, reversible assembly to form dimer and tetramer species. The tetramer can then undergo a conformational change and nucleate highly stable functional amyloid fibrils. In this study, multiple techniques including analytical ultracentrifugation (AUC) and small-angle X-ray scattering (SAXS) are used to probe a panel of B-repeat mutant constructs that assemble to distinct oligomeric states to define the structural characteristics of B-repeat dimer and tetramer species. The B-repeat region from Aap forms an extremely elongated conformation that presents several challenges for standard SAXS analyses. Specialized approaches, such as cross-sectional analyses, allowed for in-depth interpretation of data, while explicit-solvent calculations via WAXSiS allowed for accurate evaluation of atomistic models. The resulting models suggest mechanisms by which Aap functional amyloid fibrils form, illuminating an important contributing factor to recurrent staphylococcal infections.
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Affiliation(s)
- Alexander E Yarawsky
- Division of Immunobiology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Jesse B Hopkins
- The Biophysics Collaborative Access Team (BioCAT), Department of Biological Sciences, Illinois Institute of Technology, Chicago, IL, USA
| | - Leonie Chatzimagas
- Theoretical Physics and Center for Biophysics, Saarland University, Saarbrücken, Germany
| | - Jochen S Hub
- Theoretical Physics and Center for Biophysics, Saarland University, Saarbrücken, Germany
| | - Andrew B Herr
- Division of Immunobiology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA; Division of Infectious Diseases, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA; Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA.
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Yarawsky AE, Herr AB. The staphylococcal biofilm protein Aap forms a tetrameric species as a necessary intermediate before amyloidogenesis. J Biol Chem 2020; 295:12840-12850. [PMID: 32665400 DOI: 10.1074/jbc.ra120.013936] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Revised: 06/29/2020] [Indexed: 11/06/2022] Open
Abstract
The accumulation-associated protein (Aap) from Staphylococcus epidermidis is a biofilm-related protein that was found to be a critical factor for infection using a rat catheter model. The B-repeat superdomain of Aap, composed of 5-17 B-repeats, each containing a Zn2+-binding G5 and a spacer subdomain, is responsible for Zn2+-dependent assembly leading to accumulation of bacteria during biofilm formation. We previously demonstrated that a minimal B-repeat construct (Brpt1.5) forms an antiparallel dimer in the presence of 2-3 Zn2+ ions. More recently, we have reported the presence of functional amyloid-like fibrils composed of Aap within S. epidermidis biofilms and demonstrated that a biologically relevant construct containing five and a half B-repeats (Brpt5.5) forms amyloid-like fibrils similar to those observed in the biofilm. In this study, we analyze the initial assembly events of the Brpt5.5 construct. Analytical ultracentrifugation was utilized to determine hydrodynamic parameters of reversibly associating species and to perform linked equilibrium studies. Linkage studies indicated a mechanism of Zn2+-induced dimerization similar to smaller constructs; however, Brpt5.5 dimers could then undergo further Zn2+-induced assembly into a previously uncharacterized tetramer. This led us to search for potential Zn2+-binding sites outside of the dimer interface. We developed a Brpt5.5 mutant that was unable to form the tetramer and was concordantly incapable of amyloidogenesis. CD and dynamic light scattering indicate that a conformational transition in the tetramer species is a critical step preceding amyloidogenesis. This mechanistic model for B-repeat assembly and amyloidogenesis provides new avenues for potential therapeutic targeting of staphylococcal biofilms.
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Affiliation(s)
- Alexander E Yarawsky
- Graduate Program in Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA; Division of Immunobiology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA
| | - Andrew B Herr
- Division of Immunobiology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA; Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA; Division of Infectious Diseases, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA.
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Yarawsky AE, Johns SL, Schuck P, Herr AB. The biofilm adhesion protein Aap from Staphylococcus epidermidis forms zinc-dependent amyloid fibers. J Biol Chem 2020; 295:4411-4427. [PMID: 32102851 DOI: 10.1074/jbc.ra119.010874] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Revised: 02/23/2020] [Indexed: 12/17/2022] Open
Abstract
The skin-colonizing commensal bacterium Staphylococcus epidermidis is a leading cause of hospital-acquired and device-related infections. Its pathogenicity in humans is largely due to its propensity to form biofilms, surface-adherent bacterial accumulations that are remarkably resistant to chemical and physical stresses. Accumulation-associated protein (Aap) from S. epidermidis has been shown to be necessary and sufficient for mature biofilm formation and catheter infection. Aap contains up to 17 tandem B-repeat domains, capable of zinc-dependent assembly into twisted, rope-like intercellular filaments in the biofilm. Using microscopic and biophysical techniques, we show here that Aap B-repeat constructs assemble further into zinc-dependent functional amyloid fibers. We observed such amyloid fibers by confocal microscopy during both early and late stages of S. epidermidis biofilm formation, and we confirmed that extracellular fibrils from these biofilms contain Aap. Unlike what has been observed for amyloidogenic biofilm proteins from other bacteria, which typically use chaperones or initiator proteins to initiate amyloid assembly, our findings indicate that Aap from S. epidermidis requires Zn2+ as a catalyst that drives amyloid fiber formation, similar to many mammalian amyloid-forming proteins that require metals for assembly. This work provides detailed insights into S. epidermidis biofilm formation and architecture that improve our understanding of persistent staphylococcal infections.
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Affiliation(s)
- Alexander E Yarawsky
- Graduate Program in Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267.,Division of Immunobiology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229
| | - Stefanie L Johns
- Graduate Program in Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267
| | - Peter Schuck
- Dynamics of Macromolecular Assembly Section, Laboratory of Cellular Imaging and Bioengineering, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, Maryland 20814
| | - Andrew B Herr
- Division of Immunobiology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229 .,Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, Ohio 45229.,Division of Infectious Diseases, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229
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Abstract
PURPOSE OF REVIEW Atopic dermatitis (AD) is a chronic, relapsing inflammatory skin disorder that is a major public health burden worldwide. AD lesions are often colonized by Staphylococcus aureus and Staphylococcus epidermidis. An important aspect of Staphylococcus spp. is their propensity to form biofilms, adhesive surface-attached colonies that become highly resistant to antibiotics and immune responses, and recent studies have found that clinical isolates colonizing AD skin are often biofilm-positive. Biofilm formation results in complex bacterial communities that have unique effects on keratinocytes and host immunity. This review will summarize recent studies exploring the role of staphyloccocal biofilms in atopic dermatitis and the implications for treatment. RECENT FINDINGS Recent studies suggest an important role for biofilms in the pathogenesis of numerous dermatologic diseases including AD. S. aureus biofilms have been found to colonize the eccrine ducts of AD skin, and these biofilms influence secretion of keratinocyte cytokines and trigger differentiation and apoptosis of keratinocytes. These activities may act to disrupt barrier function and promote disease pathogenesis as well as allergen sensitization. Formation of biofilm is a successful strategy that protects the bacteria from environmental danger, antibiotics, and phagocytosis, enabling chronic persistence in the host. An increasing number of S. aureus skin isolates are resistant to conventional antibiotics, and staphylococcal biofilm communities are prevalent on the skin of individuals with AD. Staphylococcal colonization of the skin impacts skin barrier function and plays multiple important roles in AD pathogenesis.
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Chaton CT, Herr AB. Defining the metal specificity of a multifunctional biofilm adhesion protein. Protein Sci 2017; 26:1964-1973. [PMID: 28707417 DOI: 10.1002/pro.3232] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Revised: 07/05/2017] [Accepted: 07/07/2017] [Indexed: 12/12/2022]
Abstract
The accumulation associated protein (Aap) of Staphylococcus epidermidis mediates intercellular adhesion events necessary for biofilm growth. This process depends upon Zn2+ -induced self-assembly of G5 domains within the B-repeat region of the protein, forming anti-parallel, intertwined protein "ropes" between cells. Pleomorphism in the Zn2+ -coordinating residues was observed in previously solved crystal structures, suggesting that the metal binding site might accommodate other transition metals and thereby support dimerization. By use of carefully selected buffer systems and a specialized approach to analyze sedimentation velocity analytical ultracentrifugation data, we were able to analyze low-affinity metal binding events in solution. Our data show that both Zn2+ and Cu2+ support B-repeat assembly, whereas Mn2+ , Co2+ , and Ni2+ bind to Aap but do not support self-association. As the number of G5 domains are increased in longer B-repeat constructs, the total concentration of metal required for dimerization decreases and the transition between monomer and dimer becomes more abrupt. These characteristics allow Aap to function as an environmental sensor that regulates biofilm formation in response to local concentrations of Zn2+ and Cu2+ , both of which are implicated in immune cell activity.
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Affiliation(s)
- Catherine T Chaton
- Graduate Program in Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio.,Division of Immunobiology and Center for Systems Immunology, Division of Infectious Diseases, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, 45229
| | - Andrew B Herr
- Division of Immunobiology and Center for Systems Immunology, Division of Infectious Diseases, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, 45229
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