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Siemer AB. What makes functional amyloids work? Crit Rev Biochem Mol Biol 2022; 57:399-411. [PMID: 35997712 PMCID: PMC9588633 DOI: 10.1080/10409238.2022.2113030] [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: 01/25/2022] [Revised: 06/29/2022] [Accepted: 08/10/2022] [Indexed: 01/27/2023]
Abstract
Although first described in the context of disease, cross-β (amyloid) fibrils have also been found as functional entities in all kingdoms of life. However, what are the specific properties of the cross-β fibril motif that convey biological function, make them especially suited for their particular purpose, and distinguish them from other fibrils found in biology? This review approaches these questions by arguing that cross-β fibrils are highly periodic, stable, and self-templating structures whose formation is accompanied by substantial conformational change that leads to a multimerization of their core and framing sequences. A discussion of each of these properties is followed by selected examples of functional cross-β fibrils that show how function is usually achieved by leveraging many of these properties.
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Affiliation(s)
- Ansgar B Siemer
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
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2
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Golan N, Schwartz-Perov S, Landau M, Lipke PN. Structure and Conservation of Amyloid Spines From the Candida albicans Als5 Adhesin. Front Mol Biosci 2022; 9:926959. [PMID: 35874616 PMCID: PMC9306254 DOI: 10.3389/fmolb.2022.926959] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2022] [Accepted: 06/09/2022] [Indexed: 12/30/2022] Open
Abstract
Candida Als family adhesins mediate adhesion to biological and abiotic substrates, as well as fungal cell aggregation, fungal-bacterial co-aggregation and biofilm formation. The activity of at least two family members, Als5 and Als1, is dependent on amyloid-like protein aggregation that is initiated by shear force. Each Als adhesin has a ∼300-residue N-terminal Ig-like/invasin region. The following 108-residue, low complexity, threonine-rich (T) domain unfolds under shear force to expose a critical amyloid-forming segment 322SNGIVIVATTRTV334 at the interface between the Ig-like/invasin domain 2 and the T domain of Candida albicans Als5. Amyloid prediction programs identified six potential amyloidogenic sequences in the Ig-like/invasin region and three others in the T domain of C. albicans Als5. Peptides derived from four of these sequences formed fibrils that bound thioflavin T, the amyloid indicator dye, and three of these revealed atomic-resolution structures of cross-β spines. These are the first atomic-level structures for fungal adhesins. One of these segments, from the T domain, revealed kinked β-sheets, similarly to LARKS (Low-complexity, Amyloid-like, Reversible, Kinked segments) found in human functional amyloids. Based on the cross-β structures in Als proteins, we use evolutionary arguments to identify functional amyloidogenic sequences in other fungal adhesins, including adhesins from Candida auris. Thus, cross-β structures are often involved in fungal pathogenesis and potentially in antifungal therapy.
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Affiliation(s)
- Nimrod Golan
- Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel
| | | | - Meytal Landau
- Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel
- European Molecular Biology Laboratory (EMBL) and Centre for Structural Systems Biology, Hamburg, Germany
- *Correspondence: Meytal Landau, ; Peter N. Lipke,
| | - Peter N. Lipke
- Biology Department, Brooklyn College of the City University of New York, Brooklyn, NY, United States
- *Correspondence: Meytal Landau, ; Peter N. Lipke,
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3
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Recombinant FimH Adhesin Demonstrates How the Allosteric Catch Bond Mechanism Can Support Fast and Strong Bacterial Attachment in the Absence of Shear. J Mol Biol 2022; 434:167681. [PMID: 35697293 DOI: 10.1016/j.jmb.2022.167681] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Revised: 06/07/2022] [Accepted: 06/07/2022] [Indexed: 11/23/2022]
Abstract
The FimH protein of Escherichia coli is a model two-domain adhesin that is able to mediate an allosteric catch bond mechanism of bacterial cell attachment, where the mannose-binding lectin domain switches from an 'inactive' conformation with fast binding to mannose to an 'active' conformation with slow detachment from mannose. Because mechanical tensile force favors separation of the domains and, thus, FimH activation, it has been thought that the catch bonds can only be manifested in a fluidic shear-dependent mode of adhesion. Here, we used recombinant FimH variants with a weakened inter-domain interaction and show that a fast and sustained allosteric activation of FimH can also occur under static, non-shear conditions. Moreover, it appears that lectin domain conformational activation happens intrinsically at a constant rate, independently from its ability to interact with the pilin domain or mannose. However, the latter two factors control the rate of FimH deactivation. Thus, the allosteric catch bond mechanism can be a much broader phenomenon involved in both fast and strong cell-pathogen attachments under a broad range of hydrodynamic conditions. This concept that allostery can enable more effective receptor-ligand interactions is fundamentally different from the conventional wisdom that allostery provides a mechanism to turn binding off under specific conditions.
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4
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FLO11, a Developmental Gene Conferring Impressive Adaptive Plasticity to the Yeast Saccharomyces cerevisiae. Pathogens 2021; 10:pathogens10111509. [PMID: 34832664 PMCID: PMC8617999 DOI: 10.3390/pathogens10111509] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Revised: 11/17/2021] [Accepted: 11/18/2021] [Indexed: 12/30/2022] Open
Abstract
The yeast Saccharomyces cerevisiae has a remarkable ability to adapt its lifestyle to fluctuating or hostile environmental conditions. This adaptation most often involves morphological changes such as pseudofilaments, biofilm formation, or cell aggregation in the form of flocs. A prerequisite for these phenotypic changes is the ability to self-adhere and to adhere to abiotic surfaces. This ability is conferred by specialized surface proteins called flocculins, which are encoded by the FLO genes family in this yeast species. This mini-review focuses on the flocculin encoded by FLO11, which differs significantly from other flocculins in domain sequence and mode of genetic and epigenetic regulation, giving it an impressive plasticity that enables yeast cells to swiftly adapt to hostile environments or into new ecological niches. Furthermore, the common features of Flo11p with those of adhesins from pathogenic yeasts make FLO11 a good model to study the molecular mechanism underlying cell adhesion and biofilm formation, which are part of the initial step leading to fungal infections.
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5
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Bouyx C, Schiavone M, Teste MA, Dague E, Sieczkowski N, Julien A, François JM. The dual role of amyloid-β-sheet sequences in the cell surface properties of FLO11-encoded flocculins in Saccharomyces cerevisiae. eLife 2021; 10:e68592. [PMID: 34467855 PMCID: PMC8457840 DOI: 10.7554/elife.68592] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Accepted: 08/29/2021] [Indexed: 11/21/2022] Open
Abstract
Fungal adhesins (Als) or flocculins are family of cell surface proteins that mediate adhesion to diverse biotic and abiotic surfaces. A striking characteristic of Als proteins originally identified in the pathogenic Candida albicans is to form functional amyloids that mediate cis-interaction leading to the formation of adhesin nanodomains and trans-interaction between amyloid sequences of opposing cells. In this report, we show that flocculins encoded by FLO11 in Saccharomyces cerevisiae behave like adhesins in C. albicans. To do so, we show that the formation of nanodomains under an external physical force requires a threshold number of amyloid-forming sequences in the Flo11 protein. Then, using a genome editing approach, we constructed strains expressing variants of the Flo11 protein under the endogenous FLO11 promoter, leading to the demonstration that the loss of amyloid-forming sequences strongly reduces cell-cell interaction but has no effect on either plastic adherence or invasive growth in agar, both phenotypes being dependent on the N- and C-terminal ends of Flo11p. Finally, we show that the location of Flo11 is not altered either by the absence of amyloid-forming sequences or by the removal of the N- or C-terminus of the protein.
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Affiliation(s)
- Clara Bouyx
- Toulouse Biotechnology Institute, INSAToulouseFrance
| | - Marion Schiavone
- Toulouse Biotechnology Institute, INSAToulouseFrance
- Lallemand, Lallemand SASBlagnacFrance
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6
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Kumar A. The Complex Genetic Basis and Multilayered Regulatory Control of Yeast Pseudohyphal Growth. Annu Rev Genet 2021; 55:1-21. [PMID: 34280314 DOI: 10.1146/annurev-genet-071719-020249] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Eukaryotic cells are exquisitely responsive to external and internal cues, achieving precise control of seemingly diverse growth processes through a complex interplay of regulatory mechanisms. The budding yeast Saccharomyces cerevisiae provides a fascinating model of cell growth in its stress-responsive transition from planktonic single cells to a filamentous pseudohyphal growth form. During pseudohyphal growth, yeast cells undergo changes in morphology, polarity, and adhesion to form extended and invasive multicellular filaments. This pseudohyphal transition has been studied extensively as a model of conserved signaling pathways regulating cell growth and for its relevance in understanding the pathogenicity of the related opportunistic fungus Candida albicans, wherein filamentous growth is required for virulence. This review highlights the broad gene set enabling yeast pseudohyphal growth, signaling pathways that regulate this process, the role and regulation of proteins conferring cell adhesion, and interesting regulatory mechanisms enabling the pseudohyphal transition. Expected final online publication date for the Annual Review of Genetics, Volume 55 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Anuj Kumar
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA;
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7
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Abstract
When protein/peptides aggregate, they usually form the amyloid state consisting of cross β-sheet structure built by repetitively stacked β-strands forming long fibrils. Amyloids are usually associated with disease including Alzheimer's. However, amyloid has many useful features. It efficiently transforms protein from the soluble to the insoluble state in an essentially two-state process, while its repetitive structure provides high stability and a robust prion-like replication mechanism. Accordingly, amyloid is used by nature in multifaceted and ingenious ways of life, ranging from bacteria and fungi to mammals. These include (1) Structure: Templating for small chemical molecules (Pmel17), biofilm formation in bacteria (curli), assisting aerial hyphae formation in streptomycetes (chaplins) or monolayer formation at a surface (hydrophobins). (2) Reservoirs: A storage state for peptide/proteins to protect them from their surroundings or vice versa (storage of peptide hormones in mammalian secretory granules or major basic protein in eosinophils). (3) Information carriers: The fungal immune system (HET-s prion in Podospora anserina, yeast prions) or long-term memory (e.g., mnemons in yeast, cytoplasmic polyadenylation element-binding protein in aplysia). Aggregation is also used to (4) "suppress" the function of the soluble protein (e.g., Cdc19 in yeast stress granules), or (5) "signaling" through formation of oligomers (e.g., HET-s prion, necroptosis-related proteins RIP1/RIP3). This review summarizes current knowledge on functional amyloids with a focus on the amyloid systems curli in bacteria, HET-s prion in P. anserina, and peptide hormone storage in mammals together with an attempt to highlight differences between functional and disease-associated amyloids.
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Affiliation(s)
- Daniel Otzen
- iNANO, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Roland Riek
- Laboratory of Physical Chemistry, Swiss Federal Institute of Technology, CH-8093 Zürich, Switzerland
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8
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Ho V, Herman-Bausier P, Shaw C, Conrad KA, Garcia-Sherman MC, Draghi J, Dufrene YF, Lipke PN, Rauceo JM. An Amyloid Core Sequence in the Major Candida albicans Adhesin Als1p Mediates Cell-Cell Adhesion. mBio 2019; 10:e01766-19. [PMID: 31594814 PMCID: PMC6786869 DOI: 10.1128/mbio.01766-19] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Accepted: 09/09/2019] [Indexed: 01/05/2023] Open
Abstract
The human fungal commensal Candida albicans can become a serious opportunistic pathogen in immunocompromised hosts. The C. albicans cell adhesion protein Als1p is a highly expressed member of a large family of paralogous adhesins. Als1p can mediate binding to epithelial and endothelial cells, is upregulated in infections, and is important for biofilm formation. Als1p includes an amyloid-forming sequence at amino acids 325 to 331, identical to the sequence in the paralogs Als5p and Als3p. Therefore, we mutated Val326 to test whether this sequence is important for activity. Wild-type Als1p (Als1pWT) and Als1p with the V326N mutation (Als1pV326N) were expressed at similar levels in a Saccharomyces cerevisiae surface display model. Als1pV326N cells adhered to bovine serum albumin (BSA)-coated beads similarly to Als1pWT cells. However, cells displaying Als1pV326N showed visibly smaller aggregates and did not fluoresce in the presence of the amyloid-binding dye Thioflavin-T. A new analysis tool for single-molecule force spectroscopy-derived surface mapping showed that statistically significant force-dependent Als1p clustering occurred in Als1pWT cells but was absent in Als1pV326N cells. In single-cell force spectroscopy experiments, strong cell-cell adhesion was dependent on an intact amyloid core sequence on both interacting cells. Thus, the major adhesin Als1p interacts through amyloid-like β-aggregation to cluster adhesin molecules in cis on the cell surface as well as in trans to form cell-cell bonds.IMPORTANCE Microbial cell surface adhesins control essential processes such as adhesion, colonization, and biofilm formation. In the opportunistic fungal pathogen Candida albicans, the agglutinin-like sequence (ALS) gene family encodes eight cell surface glycoproteins that mediate adherence to biotic and abiotic surfaces and cell-cell aggregation. Als proteins are critical for commensalism and virulence. Their activities include attachment and invasion of endothelial and epithelial cells, morphogenesis, and formation of biofilms on host tissue and indwelling medical catheters. At the molecular level, Als5p-mediated cell-cell aggregation is dependent on the formation of amyloid-like nanodomains between Als5p-expressing cells. A single-site mutation to valine 326 abolishes cellular aggregation and amyloid formation. Our results show that the binding characteristics of Als1p follow a mechanistic model similar to Als5p, despite its differential expression and biological roles.
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Affiliation(s)
- Vida Ho
- Department of Sciences, John Jay College of the City University of New York, New York, New York, USA
| | | | - Christopher Shaw
- Department of Sciences, John Jay College of the City University of New York, New York, New York, USA
| | - Karen A Conrad
- Department of Sciences, John Jay College of the City University of New York, New York, New York, USA
| | - Melissa C Garcia-Sherman
- Biology Department, Brooklyn College of the City University of New York, Brooklyn, New York, USA
| | - Jeremy Draghi
- Biology Department, Brooklyn College of the City University of New York, Brooklyn, New York, USA
| | - Yves F Dufrene
- Institute of Life Sciences, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
| | - Peter N Lipke
- Biology Department, Brooklyn College of the City University of New York, Brooklyn, New York, USA
| | - Jason M Rauceo
- Department of Sciences, John Jay College of the City University of New York, New York, New York, USA
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9
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Dehullu J, Valotteau C, Herman-Bausier P, Garcia-Sherman M, Mittelviefhaus M, Vorholt JA, Lipke PN, Dufrêne YF. Fluidic Force Microscopy Demonstrates That Homophilic Adhesion by Candida albicans Als Proteins Is Mediated by Amyloid Bonds between Cells. NANO LETTERS 2019; 19:3846-3853. [PMID: 31038969 PMCID: PMC6638552 DOI: 10.1021/acs.nanolett.9b01010] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The fungal pathogen Candida albicans frequently forms drug-resistant biofilms in hospital settings and in chronic disease patients. Cell adhesion and biofilm formation involve a family of cell surface Als (agglutinin-like sequence) proteins. It is now well documented that amyloid-like clusters of laterally arranged Als proteins activate cell-cell adhesion under mechanical stress, but whether amyloid-like bonds form between aggregating cells is not known. To address this issue, we measure the forces driving Als5-mediated intercellular adhesion using an innovative fluidic force microscopy platform. Strong cell-cell adhesion is dependent on expression of amyloid-forming Als5 at high cell surface density and is inhibited by a short antiamyloid peptide. Furthermore, there is greatly attenuated binding between cells expressing amyloid-forming Als5 and cells with a nonamyloid form of Als5. Thus, homophilic bonding between Als5 proteins on adhering cells is the major mode of fungal aggregation, rather than protein-ligand interactions. These results point to a model whereby amyloid-like β-sheet interactions play a dual role in cell-cell adhesion, that is, in formation of adhesin nanoclusters ( cis-interactions) and in homophilic bonding between amyloid sequences on opposing cells ( trans-interactions). Because potential amyloid-forming sequences are found in many microbial adhesins, we speculate that this novel mechanism of amyloid-based homophilic adhesion might be widespread and could represent an interesting target for treating biofilm-associated infections.
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Affiliation(s)
- Jérôme Dehullu
- Institute of Life Sciences, Université catholique de Louvain, Croix du Sud, 4-5, bte L7.07.06, B-1348 Louvain-la-Neuve, Belgium
| | - Claire Valotteau
- Institute of Life Sciences, Université catholique de Louvain, Croix du Sud, 4-5, bte L7.07.06, B-1348 Louvain-la-Neuve, Belgium
| | - Philippe Herman-Bausier
- Institute of Life Sciences, Université catholique de Louvain, Croix du Sud, 4-5, bte L7.07.06, B-1348 Louvain-la-Neuve, Belgium
| | - Melissa Garcia-Sherman
- Biology Department, City University of New York Brooklyn College, 2900 Bedford Avenue, Brooklyn, New York 11210 United States
| | | | - Julia A. Vorholt
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zurich, Switzerland
| | - Peter N. Lipke
- Biology Department, City University of New York Brooklyn College, 2900 Bedford Avenue, Brooklyn, New York 11210 United States
| | - Yves F. Dufrêne
- Institute of Life Sciences, Université catholique de Louvain, Croix du Sud, 4-5, bte L7.07.06, B-1348 Louvain-la-Neuve, Belgium
- Walloon Excellence in Life sciences and Biotechnology (WELBIO), 4000 Liege, Belgium
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10
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von Ranke NL, Bello ML, Cabral LM, Castro HC, Rodrigues CR. Molecular modeling and dynamic simulations of agglutinin-like family members from Candida albicans: New insights into potential targets for the treatment of candidiasis. J Biomol Struct Dyn 2018; 36:4352-4365. [DOI: 10.1080/07391102.2017.1417159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- Natalia L. von Ranke
- Instituto de Biologia, Universidade Federal Fluminense, 24210-130 Niterói, RJ, Brazil
- Faculdade de Farmácia, Universidade Federal do Rio de Janeiro, 21941-902 Rio de Janeiro, RJ, Brazil
| | - Murilo L. Bello
- Faculdade de Farmácia, Universidade Federal do Rio de Janeiro, 21941-902 Rio de Janeiro, RJ, Brazil
| | - Lucio M. Cabral
- Faculdade de Farmácia, Universidade Federal do Rio de Janeiro, 21941-902 Rio de Janeiro, RJ, Brazil
| | - Helena C. Castro
- Instituto de Biologia, Universidade Federal Fluminense, 24210-130 Niterói, RJ, Brazil
| | - Carlos R. Rodrigues
- Faculdade de Farmácia, Universidade Federal do Rio de Janeiro, 21941-902 Rio de Janeiro, RJ, Brazil
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11
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Impact of Fungal MAPK Pathway Targets on the Cell Wall. J Fungi (Basel) 2018; 4:jof4030093. [PMID: 30096860 PMCID: PMC6162559 DOI: 10.3390/jof4030093] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Revised: 07/31/2018] [Accepted: 08/02/2018] [Indexed: 12/14/2022] Open
Abstract
The fungal cell wall is an extracellular organelle that provides structure and protection to cells. The cell wall also influences the interactions of cells with each other and surfaces. The cell wall can be reorganized in response to changing environmental conditions and different types of stress. Signaling pathways control the remodeling of the cell wall through target proteins that are in many cases not well defined. The Mitogen Activated Protein Kinase pathway that controls filamentous growth in yeast (fMAPK) was required for normal growth in media containing the cell wall perturbing agent Calcofluor White (CFW). A mass spectrometry (MASS-SPEC) approach and analysis of expression profiling data identified cell wall proteins and modifying enzymes whose levels were influenced by the fMAPK pathway. These include Flo11p, Flo10p, Tip1p, Pry2p and the mannosyltransferase, Och1p. Cells lacking Flo11p or Och1p were sensitive to CFW. The identification of cell wall proteins controlled by a MAPK pathway may provide insights into how signaling pathways regulate the cell wall.
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12
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Lipke PN. What We Do Not Know about Fungal Cell Adhesion Molecules. J Fungi (Basel) 2018; 4:jof4020059. [PMID: 29772751 PMCID: PMC6023273 DOI: 10.3390/jof4020059] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2018] [Revised: 04/27/2018] [Accepted: 05/10/2018] [Indexed: 12/16/2022] Open
Abstract
There has been extensive research on structure and function of fungal cell adhesion molecules, but the most of the work has been about adhesins in Candida albicans and Saccharomyces cerevisiae. These yeasts are members of a single ascomycete order, and adhesion molecules from the six other fungal phyla are only sparsely described in the literature. In these other phyla, most of the research is at the cellular level, rather than at the molecular level, so there has been little characterization of the adhesion molecules themselves. A catalog of known adhesins shows some common features: high Ser/Thr content, tandem repeats, N- and O-glycosylations, GPI anchors, dibasic sequence motifs, and potential amyloid-forming sequences. However, none of these features is universal. Known ligands include proteins and glycans on homologous cells and host cells. Existing and novel tools can exploit the availability of genome sequences to identify and characterize new fungal adhesins. These include bioinformatics tools and well-established yeast surface display models, which could be coupled with an adhesion substrate array. Thus, new knowledge could be exploited to answer key questions in fungal ecology, animal and plant pathogenesis, and roles of biofilms in infection and biomass turnover.
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Affiliation(s)
- Peter N Lipke
- Biology Department, Brooklyn College, City University of New York, Brooklyn, NY 11210, USA.
- The Graduate Center, City University of New York, New York, NY 10016, USA.
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13
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Role of the Inducible Adhesin CpAls7 in Binding of Candida parapsilosis to the Extracellular Matrix under Fluid Shear. Infect Immun 2018; 86:IAI.00892-17. [PMID: 29378793 DOI: 10.1128/iai.00892-17] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2017] [Accepted: 01/20/2018] [Indexed: 12/12/2022] Open
Abstract
The yeast Candida parapsilosis is an increasingly common cause of systemic fungal infections among immunocompromised individuals, including premature infants. Adhesion to host surfaces is an important step in pathogenesis, but this process has not been extensively studied in this organism. A microfluidics assay was developed to test the ability of C. parapsilosis to adhere to immobilized host extracellular matrix proteins under physiological fluid shear conditions. Growth in mammalian tissue culture medium at 37°C for 3 to 6 h led to the induction of an adhesive phenotype at shear forces of 1 to 5 dynes/cm2 in some isolates of C. parapsilosis Glutamic acid, proline, and calcium appeared to be the minimally necessary requirements for increased adhesion in these assays. To determine whether genes homologous to the ALS gene family of C. albicans were important for the adhesive phenotype, the expression levels of 5 homologous C. parapsilosis genes were quantified by using quantitative PCR (qPCR) under conditions leading to increased adhesion. CPAR2_404800 (CpALS7) and CPAR2_404780 showed increased expression levels compared to those in control yeast. The extent of adhesion was variable among different isolates, and linear regression identified the expression of CpALS7 but not CPAR2_404780 as having a strong positive correlation with adhesion. A homozygous CpALS7 deletion strain was deficient in adhesion, whereas the expression of CpALS7 in Saccharomyces cerevisiae resulted in increased adhesion. Together, these data provide strong evidence that CpAls7 aids in the adherence of C. parapsilosis to the extracellular matrix under shear forces and support its previously reported role in virulence.
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14
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Amyloid-Like β-Aggregates as Force-Sensitive Switches in Fungal Biofilms and Infections. Microbiol Mol Biol Rev 2017; 82:82/1/e00035-17. [PMID: 29187516 DOI: 10.1128/mmbr.00035-17] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Cellular aggregation is an essential step in the formation of biofilms, which promote fungal survival and persistence in hosts. In many of the known yeast cell adhesion proteins, there are amino acid sequences predicted to form amyloid-like β-aggregates. These sequences mediate amyloid formation in vitro. In vivo, these sequences mediate a phase transition from a disordered state to a partially ordered state to create patches of adhesins on the cell surface. These β-aggregated protein patches are called adhesin nanodomains, and their presence greatly increases and strengthens cell-cell interactions in fungal cell aggregation. Nanodomain formation is slow (with molecular response in minutes and the consequences being evident for hours), and strong interactions lead to enhanced biofilm formation. Unique among functional amyloids, fungal adhesin β-aggregation can be triggered by the application of physical shear force, leading to cellular responses to flow-induced stress and the formation of robust biofilms that persist under flow. Bioinformatics analysis suggests that this phenomenon may be widespread. Analysis of fungal abscesses shows the presence of surface amyloids in situ, a finding which supports the idea that phase changes to an amyloid-like state occur in vivo. The amyloid-coated fungi bind the damage-associated molecular pattern receptor serum amyloid P component, and there may be a consequential modulation of innate immune responses to the fungi. Structural data now suggest mechanisms for the force-mediated induction of the phase change. We summarize and discuss evidence that the sequences function as triggers for protein aggregation and subsequent cellular aggregation, both in vitro and in vivo.
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15
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Abstract
We focus this article on turning a biofilm inside out. The "inside" of the biofilm comprises the individual biofilm-related phenotypes, their environmental drivers and genetic determinants, and the coordination of gene functions through transcriptional regulators. Investigators have viewed the inside of the biofilm through diverse approaches, and this article will attempt to capture the essence of many. The ultimate goal is to connect the inside to the "outside," which we view as biofilm structure, development, pharmacological attributes, and medical impact.
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16
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Abstract
We focus this article on turning a biofilm inside out. The "inside" of the biofilm comprises the individual biofilm-related phenotypes, their environmental drivers and genetic determinants, and the coordination of gene functions through transcriptional regulators. Investigators have viewed the inside of the biofilm through diverse approaches, and this article will attempt to capture the essence of many. The ultimate goal is to connect the inside to the "outside," which we view as biofilm structure, development, pharmacological attributes, and medical impact.
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Affiliation(s)
- Katherine Lagree
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Aaron P Mitchell
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213
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17
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Force Sensitivity in Saccharomyces cerevisiae Flocculins. mSphere 2016; 1:mSphere00128-16. [PMID: 27547825 PMCID: PMC4989244 DOI: 10.1128/msphere.00128-16] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 06/27/2016] [Indexed: 12/28/2022] Open
Abstract
The Saccharomyces cerevisiae flocculins mediate the formation of cellular aggregates and biofilm-like mats, useful in clearing yeast from fermentations. An important property of fungal adhesion proteins, including flocculins, is the ability to form catch bonds, i.e., bonds that strengthen under tension. This strengthening is based, at least in part, on increased avidity of binding due to clustering of adhesins in cell surface nanodomains. This clustering depends on amyloid-like β-aggregation of short amino acid sequences in the adhesins. In Candida albicans adhesin Als5, shear stress from vortex mixing can unfold part of the protein to expose aggregation-prone sequences, and then adhesins aggregate into nanodomains. We therefore tested whether shear stress from mixing can increase flocculation activity by potentiating similar protein remodeling and aggregation in the flocculins. The results demonstrate the applicability of the Als adhesin model and provide a rational framework for the enhancement or inhibition of flocculation in industrial applications. Many fungal adhesins have short, β-aggregation-prone sequences that play important functional roles, and in the Candida albicans adhesin Als5p, these sequences cluster the adhesins after exposure to shear force. Here, we report that Saccharomyces cerevisiae flocculins Flo11p and Flo1p have similar β-aggregation-prone sequences and are similarly stimulated by shear force, despite being nonhomologous. Shear from vortex mixing induced the formation of small flocs in cells expressing either adhesin. After the addition of Ca2+, yeast cells from vortex-sheared populations showed greatly enhanced flocculation and displayed more pronounced thioflavin-bright surface nanodomains. At high concentrations, amyloidophilic dyes inhibited Flo1p- and Flo11p-mediated agar invasion and the shear-induced increase in flocculation. Consistent with these results, atomic force microscopy of Flo11p showed successive force-distance peaks characteristic of sequentially unfolding tandem repeat domains, like Flo1p and Als5p. Flo11p-expressing cells bound together through homophilic interactions with adhesion forces of up to 700 pN and rupture lengths of up to 600 nm. These results are consistent with the potentiation of yeast flocculation by shear-induced formation of high-avidity domains of clustered adhesins at the cell surface, similar to the activation of Candida albicans adhesin Als5p. Thus, yeast adhesins from three independent gene families use similar force-dependent interactions to drive cell adhesion. IMPORTANCE The Saccharomyces cerevisiae flocculins mediate the formation of cellular aggregates and biofilm-like mats, useful in clearing yeast from fermentations. An important property of fungal adhesion proteins, including flocculins, is the ability to form catch bonds, i.e., bonds that strengthen under tension. This strengthening is based, at least in part, on increased avidity of binding due to clustering of adhesins in cell surface nanodomains. This clustering depends on amyloid-like β-aggregation of short amino acid sequences in the adhesins. In Candida albicans adhesin Als5, shear stress from vortex mixing can unfold part of the protein to expose aggregation-prone sequences, and then adhesins aggregate into nanodomains. We therefore tested whether shear stress from mixing can increase flocculation activity by potentiating similar protein remodeling and aggregation in the flocculins. The results demonstrate the applicability of the Als adhesin model and provide a rational framework for the enhancement or inhibition of flocculation in industrial applications.
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Lin J, Wester MJ, Graus MS, Lidke KA, Neumann AK. Nanoscopic cell-wall architecture of an immunogenic ligand in Candida albicans during antifungal drug treatment. Mol Biol Cell 2016; 27:1002-14. [PMID: 26792838 PMCID: PMC4791122 DOI: 10.1091/mbc.e15-06-0355] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Accepted: 01/12/2016] [Indexed: 12/25/2022] Open
Abstract
Candida albicans evades immunity by limiting cell-wall β-glucan exposure. dSTORM imaging reveals that “unmasking”of glucan by an antifungal drug occurs through nanoscale reorganization of glucan exposure geometry. Nanostructuring of glucan might play a role in innate immune activation and provides insights into the physical regulation of glucan exposure. The cell wall of Candida albicans is composed largely of polysaccharides. Here we focus on β-glucan, an immunogenic cell-wall polysaccharide whose surface exposure is often restricted, or “masked,” from immune recognition by Dectin-1 on dendritic cells (DCs) and other innate immune cells. Previous research suggested that the physical presentation geometry of β-glucan might determine whether it can be recognized by Dectin-1. We used direct stochastic optical reconstruction microscopy to explore the fine structure of β-glucan exposed on C. albicans cell walls before and after treatment with the antimycotic drug caspofungin, which alters glucan exposure. Most surface-accessible glucan on C. albicans yeast and hyphae is limited to isolated Dectin-1–binding sites. Caspofungin-induced unmasking caused approximately fourfold to sevenfold increase in total glucan exposure, accompanied by increased phagocytosis efficiency of DCs for unmasked yeasts. Nanoscopic imaging of caspofungin-unmasked C. albicans cell walls revealed that the increase in glucan exposure is due to increased density of glucan exposures and increased multiglucan exposure sizes. These findings reveal that glucan exhibits significant nanostructure, which is a previously unknown physical component of the host–Candida interaction that might change during antifungal chemotherapy and affect innate immune activation.
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Affiliation(s)
- Jia Lin
- Center for Spatiotemporal Modeling of Cell Signaling, University of New Mexico, Albuquerque, NM 87131 Department of Pathology, University of New Mexico, Albuquerque, NM 87131
| | - Michael J Wester
- Center for Spatiotemporal Modeling of Cell Signaling, University of New Mexico, Albuquerque, NM 87131 Department of Mathematics and Statistics, University of New Mexico, Albuquerque, NM 87131
| | - Matthew S Graus
- Center for Spatiotemporal Modeling of Cell Signaling, University of New Mexico, Albuquerque, NM 87131 Department of Pathology, University of New Mexico, Albuquerque, NM 87131
| | - Keith A Lidke
- Center for Spatiotemporal Modeling of Cell Signaling, University of New Mexico, Albuquerque, NM 87131 Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131
| | - Aaron K Neumann
- Center for Spatiotemporal Modeling of Cell Signaling, University of New Mexico, Albuquerque, NM 87131 Department of Pathology, University of New Mexico, Albuquerque, NM 87131
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The Human Disease-Associated Aβ Amyloid Core Sequence Forms Functional Amyloids in a Fungal Adhesin. mBio 2016; 7:e01815-15. [PMID: 26758179 PMCID: PMC4725003 DOI: 10.1128/mbio.01815-15] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
UNLABELLED There is increasing evidence that many amyloids in living cells have physiological functions. On the surfaces of fungal cells, amyloid core sequences in adhesins can aggregate into 100- to 1,000-nm-wide patches to form high-avidity adhesion nanodomains on the cell surface. The nanodomains form through interactions that have amyloid-like properties: binding of amyloid dyes, perturbation by antiamyloid agents, and interaction with homologous sequences. To test whether these functional interactions are mediated by typical amyloid interactions, we substituted an amyloid core sequence, LVFFA, from human Aβ protein for the native sequence IVIVA in the 1,419-residue Candida albicans adhesin Als5p. The chimeric protein formed cell surface nanodomains and mediated cellular aggregation. The native sequence and chimeric adhesins responded similarly to the amyloid dye thioflavin T and to amyloid perturbants. However, unlike the native protein, the nanodomains formed by the chimeric protein were not force activated and formed less-robust aggregates under flow. These results showed the similarity of amyloid interactions in the amyloid core sequences of native Als5p and Aβ, but they also highlighted emergent properties of the native sequence. Also, a peptide composed of the Aβ amyloid sequence flanked by amino acids from the adhesin formed two-dimensional sheets with sizes similar to the cell surface patches of the adhesins. These results inform an initial model for the structure of fungal cell surface amyloid nanodomains. IMPORTANCE Protein amyloid aggregates are markers of neurodegenerative diseases such as Alzheimer's and Parkinsonism. Nevertheless, there are also functional amyloids, including biofilm-associated amyloids in bacteria and fungi. In fungi, glycoprotein adhesins aggregate into cell surface patches through amyloid-like interactions, and the adhesin clustering strengthens cell-cell binding. These fungal surface amyloid nanodomains mediate biofilm persistence under flow, and they also moderate host inflammatory responses in fungal infections. To determine whether the amyloid-like properties of fungal surface nanodomains are sequence specific, we ask whether a disease-associated amyloid core sequence has properties equivalent to those of the native sequence in a fungal adhesin. A chimeric adhesin with an amyloid sequence from the Alzheimer's disease protein Aβ instead of its native sequence effectively clustered the adhesins on the cell surface, but it showed a different response to hydrodynamic shear. These results begin an analysis of the sequence dependence for newly discovered activities for fungal surface amyloid nanodomains.
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Rajendran A, Hu B. Mycoalgae biofilm: development of a novel platform technology using algae and fungal cultures. BIOTECHNOLOGY FOR BIOFUELS 2016; 9:112. [PMID: 27247623 PMCID: PMC4886447 DOI: 10.1186/s13068-016-0533-y] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 05/19/2016] [Indexed: 05/08/2023]
Abstract
BACKGROUND Microalgae is considered a promising source for biofuel and bioenergy production, bio-remediation and production of high-value bioactive compounds, but harvesting microalgae is a major bottleneck in the algae based processes. The objective of this research is to mimic the growth of natural lichen and develop a novel biofilm platform technology using filamentous fungi and microalgae to form a lichen type of biofilm "mycoalgae" in a supporting polymer matrix. RESULTS The possibility of co-existence of Chlorella vulgaris with various fungal cultures was tested to identify the best strain combination for high algae harvest efficiency. The effect of different matrices for cell attachment and biofilm formation, cell surface characterization of mycoalgae biofilm, kinetics of the process with respect to the algae-fungi cell distribution and total biomass production was studied. Mycoalgae biofilm with algae attachment efficiency of 99.0 % and above was achieved in a polymer-cotton composite matrix with glucose concentration of 2 g/L in the growth medium and agitation intensity of 150 rpm at 27 °C. The total biomass in the co-culture with the selected strain combination (Mucor sp. and Chlorella sp.) was higher than the axenic cultures of fungi and algae at the conditions tested. CONCLUSIONS The results show that algae can be grown with complete attachment to a bio-augmenting fungal surface and can be harvested readily as a biofilm for product extraction from biomass. Even though, interaction between heterotrophic fungi and phototrophic algae was investigated in solid media after prolonged contact in a report, this research is the first of its kind in developing an artificial lichen type biofilm called "mycoalgae" biofilm completely attached on a matrix in liquid cultures. The mycoalgae biofilm based processes, propounds the scope for exploring new avenues in the bio-production industry and bioremediation.
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Affiliation(s)
- Aravindan Rajendran
- />Department of Bioproducts and Biosystems Engineering, University of Minnesota, Room: 219, BioAgEng, 1390 Eckles Ave, St. Paul, MN 55108-6005 USA
| | - Bo Hu
- />Department of Bioproducts and Biosystems Engineering, University of Minnesota, Room: 315, 1390 Eckles Ave, Saint Paul, MN 55108-6005 USA
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21
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Chan CXJ, Joseph IG, Huang A, Jackson DN, Lipke PN. Quantitative Analyses of Force-Induced Amyloid Formation in Candida albicans Als5p: Activation by Standard Laboratory Procedures. PLoS One 2015; 10:e0129152. [PMID: 26047318 PMCID: PMC4457901 DOI: 10.1371/journal.pone.0129152] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Accepted: 05/05/2015] [Indexed: 11/18/2022] Open
Abstract
Candida albicans adhesins have amyloid-forming sequences. In Als5p, these amyloid sequences cluster cell surface adhesins to create high avidity surface adhesion nanodomains. Such nanodomains form after force is applied to the cell surface by atomic force microscopy or laminar flow. Here we report centrifuging and resuspending S. cerevisiae cells expressing Als5p led to 1.7-fold increase in initial rate of adhesion to ligand coated beads. Furthermore, mechanical stress from vortex-mixing of Als5p cells or C. albicans cells also induced additional formation of amyloid nanodomains and consequent activation of adhesion. Vortex-mixing for 60 seconds increased the initial rate of adhesion 1.6-fold. The effects of vortex-mixing were replicated in heat-killed cells as well. Activation was accompanied by increases in thioflavin T cell surface fluorescence measured by flow cytometry or by confocal microscopy. There was no adhesion activation in cells expressing amyloid-impaired Als5pV326N or in cells incubated with inhibitory concentrations of anti-amyloid dyes. Together these results demonstrated the activation of cell surface amyloid nanodomains in yeast expressing Als adhesins, and further delineate the forces that can activate adhesion in vivo. Consequently there is quantitative support for the hypothesis that amyloid forming adhesins act as both force sensors and effectors.
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Affiliation(s)
- Cho X. J. Chan
- Biology Department, Brooklyn College City University of New York, New York, New York, United States of America
- The Graduate Center, City University of New York, New York, New York, United States of America
- Haskins Laboratories and the Department of Chemistry and Physical Sciences, Pace University, New York, New York, United States of America
| | - Ivor G. Joseph
- Biology Department, Brooklyn College City University of New York, New York, New York, United States of America
| | - Andy Huang
- Biology Department, Brooklyn College City University of New York, New York, New York, United States of America
| | - Desmond N. Jackson
- Biology Department, Brooklyn College City University of New York, New York, New York, United States of America
| | - Peter N. Lipke
- Biology Department, Brooklyn College City University of New York, New York, New York, United States of America
- The Graduate Center, City University of New York, New York, New York, United States of America
- * E-mail:
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El-Kirat-Chatel S, Beaussart A, Vincent SP, Flos MA, Hols P, Lipke PN, Dufrêne YF. Forces in yeast flocculation. NANOSCALE 2015; 7:1760-1767. [PMID: 25515338 PMCID: PMC4304900 DOI: 10.1039/c4nr06315e] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
In the baker's yeast Saccharomyces cerevisiae, cell-cell adhesion ("flocculation") is conferred by a family of lectin-like proteins known as the flocculin (Flo) proteins. Knowledge of the adhesive and mechanical properties of flocculins is important for understanding the mechanisms of yeast adhesion, and may help controlling yeast behaviour in biotechnology. We use single-molecule and single-cell atomic force microscopy (AFM) to explore the nanoscale forces engaged in yeast flocculation, focusing on the role of Flo1 as a prototype of flocculins. Using AFM tips labelled with mannose, we detect single flocculins on Flo1-expressing cells, showing they are widely exposed on the cell surface. When subjected to force, individual Flo1 proteins display two distinct force responses, i.e. weak lectin binding forces and strong unfolding forces reflecting the force-induced extension of hydrophobic tandem repeats. We demonstrate that cell-cell adhesion bonds also involve multiple weak lectin interactions together with strong unfolding forces, both associated with Flo1 molecules. Single-molecule and single-cell data correlate with microscale cell adhesion behaviour, suggesting strongly that Flo1 mechanics is critical for yeast flocculation. These results favour a model in which not only weak lectin-sugar interactions are involved in yeast flocculation but also strong hydrophobic interactions resulting from protein unfolding.
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Affiliation(s)
- Sofiane El-Kirat-Chatel
- Université catholique de Louvain, Institute of Life Sciences, B-1348 Louvain-la-Neuve, Belgium
| | - Audrey Beaussart
- Université catholique de Louvain, Institute of Life Sciences, B-1348 Louvain-la-Neuve, Belgium
| | - Stéphane P. Vincent
- University of Namur, Department of Chemistry, Rue de Bruxelles 61, 5000 Namur, Belgium
| | - Marta Abellán Flos
- University of Namur, Department of Chemistry, Rue de Bruxelles 61, 5000 Namur, Belgium
| | - Pascal Hols
- Université catholique de Louvain, Institute of Life Sciences, B-1348 Louvain-la-Neuve, Belgium
| | - Peter N. Lipke
- Department of Biology, Brooklyn College of City University of New York, Brooklyn, New York 11210, USA
| | - Yves F. Dufrêne
- Université catholique de Louvain, Institute of Life Sciences, B-1348 Louvain-la-Neuve, Belgium
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Bamford CV, Nobbs AH, Barbour ME, Lamont RJ, Jenkinson HF. Functional regions of Candida albicans hyphal cell wall protein Als3 that determine interaction with the oral bacterium Streptococcus gordonii. MICROBIOLOGY-SGM 2014; 161:18-29. [PMID: 25332379 DOI: 10.1099/mic.0.083378-0] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The opportunistic pathogen Candida albicans colonizes the oral cavity and gastrointestinal tract. Adherence to host cells, extracellular matrix and salivary glycoproteins that coat oral surfaces, including prostheses, is an important prerequisite for colonization. In addition, interactions of C. albicans with commensal oral streptococci are suggested to promote retention and persistence of fungal cells in mixed-species communities. The hyphal filament specific cell wall protein Als3, a member of the Als protein family, is a major determinant in C. albicans adherence. Here, we utilized site-specific in-frame deletions within Als3 expressed on the surface of heterologous Saccharomyces cerevisiae to determine regions involved in interactions of Als3 with Streptococcus gordonii. N-terminal region amino acid residue deletions Δ166-225, Δ218-285, Δ270-305 and Δ277-286 were each effective in inhibiting binding of Strep. gordonii to Als3. In addition, these deletions differentially affected biofilm formation, hydrophobicity, and adherence to silicone and human tissue proteins. Deletion of the central repeat domain (Δ434-830) did not significantly affect interaction of Als3 with Strep. gordonii SspB protein, but affected other adherence properties and biofilm formation. Deletion of the amyloid-forming region (Δ325-331) did not affect interaction of Als3 with Strep. gordonii SspB adhesin, suggesting this interaction was amyloid-independent. These findings highlighted the essential function of the N-terminal domain of Als3 in mediating the interaction of C. albicans with S. gordonii, and suggested that amyloid formation is not essential for the inter-kingdom interaction.
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Affiliation(s)
- Caroline V Bamford
- School of Oral and Dental Sciences, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, UK
| | - Angela H Nobbs
- School of Oral and Dental Sciences, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, UK
| | - Michele E Barbour
- School of Oral and Dental Sciences, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, UK
| | - Richard J Lamont
- School of Dentistry, University of Louisville, Louisville, Kentucky, USA
| | - Howard F Jenkinson
- School of Oral and Dental Sciences, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, UK
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