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Tamura K, Foley MH, Gardill BR, Dejean G, Schnizlein M, Bahr CME, Louise Creagh A, van Petegem F, Koropatkin NM, Brumer H. Surface glycan-binding proteins are essential for cereal beta-glucan utilization by the human gut symbiont Bacteroides ovatus. Cell Mol Life Sci 2019; 76:4319-4340. [PMID: 31062073 PMCID: PMC6810844 DOI: 10.1007/s00018-019-03115-3] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Revised: 04/03/2019] [Accepted: 04/23/2019] [Indexed: 02/07/2023]
Abstract
The human gut microbiota, which underpins nutrition and systemic health, is compositionally sensitive to the availability of complex carbohydrates in the diet. The Bacteroidetes comprise a dominant phylum in the human gut microbiota whose members thrive on dietary and endogenous glycans by employing a diversity of highly specific, multi-gene polysaccharide utilization loci (PUL), which encode a variety of carbohydrases, transporters, and sensor/regulators. PULs invariably also encode surface glycan-binding proteins (SGBPs) that play a central role in saccharide capture at the outer membrane. Here, we present combined biophysical, structural, and in vivo characterization of the two SGBPs encoded by the Bacteroides ovatus mixed-linkage β-glucan utilization locus (MLGUL), thereby elucidating their key roles in the metabolism of this ubiquitous dietary cereal polysaccharide. In particular, molecular insight gained through several crystallographic complexes of SGBP-A and SGBP-B with oligosaccharides reveals that unique shape complementarity of binding platforms underpins specificity for the kinked MLG backbone vis-à-vis linear β-glucans. Reverse-genetic analysis revealed that both the presence and binding ability of the SusD homolog BoSGBPMLG-A are essential for growth on MLG, whereas the divergent, multi-domain BoSGBPMLG-B is dispensable but may assist in oligosaccharide scavenging from the environment. The synthesis of these data illuminates the critical role SGBPs play in concert with other MLGUL components, reveals new structure-function relationships among SGBPs, and provides fundamental knowledge to inform future (meta)genomic, biochemical, and microbiological analyses of the human gut microbiota.
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Affiliation(s)
- Kazune Tamura
- Michael Smith Laboratories, University of British Columbia, 2185 East Mall, Vancouver, BC, V6T 1Z4, Canada
- Department of Biochemistry and Molecular Biology, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
| | - Matthew H Foley
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, 48109, USA
| | - Bernd R Gardill
- Department of Biochemistry and Molecular Biology, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
| | - Guillaume Dejean
- Michael Smith Laboratories, University of British Columbia, 2185 East Mall, Vancouver, BC, V6T 1Z4, Canada
| | - Matthew Schnizlein
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, 48109, USA
| | - Constance M E Bahr
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, 48109, USA
| | - A Louise Creagh
- Michael Smith Laboratories, University of British Columbia, 2185 East Mall, Vancouver, BC, V6T 1Z4, Canada
- Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, BC, V6T 1Z3, Canada
| | - Filip van Petegem
- Department of Biochemistry and Molecular Biology, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
| | - Nicole M Koropatkin
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, 48109, USA.
| | - Harry Brumer
- Michael Smith Laboratories, University of British Columbia, 2185 East Mall, Vancouver, BC, V6T 1Z4, Canada.
- Department of Biochemistry and Molecular Biology, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada.
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T 1Z1, Canada.
- Department of Botany, University of British Columbia, 3200 University Boulevard, Vancouver, BC, V6T 1Z4, Canada.
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Guerra AJ, Zhang O, Bahr CME, Huynh MH, DelProposto J, Brown WC, Wawrzak Z, Koropatkin NM, Carruthers VB. Structural basis of Toxoplasma gondii perforin-like protein 1 membrane interaction and activity during egress. PLoS Pathog 2018; 14:e1007476. [PMID: 30513119 PMCID: PMC6294395 DOI: 10.1371/journal.ppat.1007476] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Revised: 12/14/2018] [Accepted: 11/19/2018] [Indexed: 11/19/2022] Open
Abstract
Intracellular pathogens must egress from the host cell to continue their infectious cycle. Apicomplexans are a phylum of intracellular protozoans that have evolved members of the membrane attack complex and perforin (MACPF) family of pore forming proteins to disrupt cellular membranes for traversing cells during tissue migration or egress from a replicative vacuole following intracellular reproduction. Previous work showed that the apicomplexan Toxoplasma gondii secretes a perforin-like protein (TgPLP1) that contains a C-terminal Domain (CTD) which is necessary for efficient parasite egress. However, the structural basis for CTD membrane binding and egress competency remained unknown. Here, we present evidence that TgPLP1 CTD prefers binding lipids that are abundant in the inner leaflet of the lipid bilayer. Additionally, solving the high-resolution crystal structure of the TgPLP1 APCβ domain within the CTD reveals an unusual double-layered β-prism fold that resembles only one other protein of known structure. Three direct repeat sequences comprise subdomains, with each constituting a wall of the β-prism fold. One subdomain features a protruding hydrophobic loop with an exposed tryptophan at its tip. Spectrophotometric measurements of intrinsic tryptophan fluorescence are consistent with insertion of the hydrophobic loop into a target membrane. Using CRISPR/Cas9 gene editing we show that parasite strains bearing mutations in the hydrophobic loop, including alanine substitution of the tip tryptophan, are equally deficient in egress as a strain lacking TgPLP1 altogether. Taken together our findings suggest a crucial role for the hydrophobic loop in anchoring TgPLP1 to the membrane to support its cytolytic activity and egress function. The intracellular parasite Toxoplasma gondii infects many hosts including humans. Infected people with a weak immune system can suffer severe disease when the parasite replicates uncontrolled via repeated cycles of cell invasion, intracellular growth, and exit, resulting in cell death. Previous studies showed that T. gondii encodes a pore-forming protein, TgPLP1, which contains an unusual domain that is crucial for efficient exit from both the parasite containing vacuole and the host cell. However, how TgPLP1 recognizes and binds to the appropriate membrane is unclear. Here we use a combination of biochemistry, structural biology, and parasitology to identify a preference of TgPLP1 for specific lipids and show that a loop within the structure of the membrane-binding domain inserts into the target membrane and is necessary for exit from the parasite containing vacuole. Our study sheds light into the determinants of membrane binding in TgPLP1 and may inform the overall mechanism of pore formation in similar systems.
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Affiliation(s)
- Alfredo J. Guerra
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI, United States of America
- * E-mail:
| | - Ou Zhang
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI, United States of America
| | - Constance M. E. Bahr
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI, United States of America
| | - My-Hang Huynh
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI, United States of America
| | - James DelProposto
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, United States of America
| | - William C. Brown
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, United States of America
| | - Zdzislaw Wawrzak
- Northwestern Synchrotron Research Center–LS-CAT, Northwestern University, Argonne, IL, United States of America
| | - Nicole M. Koropatkin
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI, United States of America
| | - Vern B. Carruthers
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI, United States of America
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