Publications
16 results found
Morrison A, 2024, Development of Improved Cultivation Methods for Environmental Microorganisms
Cultivation of bacteria remains an essential prerequisite for numerous research and biotechnological applications. Despite their ubiquity, only a minority of environmental bacteria are cultivable using standard techniques. Therefore, a vast microbial ‘dark matter’ awaits exploration for valuable therapeutics or research potential. Despite innovations in enhanced cultivation techniques, limitations remain including throughput, dependencies on environmental factors or abrupt transitions of microorganisms from native to laboratory conditions. This thesis addresses these challenges with the development, optimisation, and experimental assessment of two novel cultivation methodologies. The first methodology allows for the gradual transition and acclimatisation of microorganisms from native environments to culture media using the novel Enhanced Domestication (EDEN) device. Compared to the instantaneous transition, acclimatisation of pond water bacteria to R2A culture media significantly enhanced cultivation diversity, colony yield and greater taxonomic range of isolates including those previously reported to be recalcitrant to cultivation. Moreover, likely novel taxa cultivated with EDEN exhibited antimicrobial activity against methicillin-resistant Staphylococcus aureus. The second methodology involves the development of a cell encapsulation apparatus, termed Bacterial Encapsulation and Containment (BEAD), enabling microinjection and cultivation of bacteria within alginate hydrogel beads using an automated pneumatic pump system. The performance of in situ cultivation with BEAD-encapsulated bacteria were assessed using the newly developed cultivation cassettes growth chambers. The findings propose enhanced cultivation strategies to unlock the biosynthetic potential of uncultured environmental bacteria.
Schlösser L, Sachse C, Low HH, et al., 2023, Conserved structures of ESCRT-III superfamily members across domains of life., Trends Biochem Sci, Vol: 48, Pages: 993-1004, ISSN: 0968-0004
Structural and evolutionary studies of cyanobacterial phage shock protein A (PspA) and inner membrane-associated protein of 30 kDa (IM30) have revealed that these proteins belong to the endosomal sorting complex required for transport-III (ESCRT-III) superfamily, which is conserved across all three domains of life. PspA and IM30 share secondary and tertiary structures with eukaryotic ESCRT-III proteins, whilst also oligomerizing via conserved interactions. Here, we examine the structures of bacterial ESCRT-III-like proteins and compare the monomeric and oligomerized forms with their eukaryotic counterparts. We discuss conserved interactions used for self-assembly and highlight key hinge regions that mediate oligomer ultrastructure versatility. Finally, we address the differences in nomenclature assigned to equivalent structural motifs in both the bacterial and eukaryotic fields and suggest a common nomenclature applicable across the ESCRT-III superfamily.
Low H, Tassinari M, Filloux A, et al., 2023, Assembly mechanism of a Tad secretion system secretin-pilotin complex, Nature Communications, Vol: 14, ISSN: 2041-1723
The bacterial Tight adherence Secretion System (TadSS) assembles surface pili that drive cell adherence, biofilm formation and bacterial predation. The structure and mechanism of the TadSS is mostly unknown. This includes characterisation of the outer membrane secretin through which the pilus is channelled and recruitment of its pilotin. Here we investigate RcpA and TadD lipoprotein from Pseudomonas aeruginosa. Light microscopy reveals RcpA colocalising with TadD in P. aeruginosa and when heterologously expressed in Escherichia coli. We use cryogenic electron microscopy to determine how RcpA and TadD assemble a secretin channel with C13 and C14 symmetries. Despite low sequence homology, we show that TadD shares a similar fold to the type 4 pilus system pilotin PilF. We establish that the C-terminal four residues of RcpA bind TadD - an interaction essential for secretin formation. The binding mechanism between RcpA and TadD appears distinct from known secretin-pilotin pairings in other secretion systems.
Liu J, Tassinari M, Naskar S, et al., 2021, Bacterial Vipp1 and PspA are members of the ancient ESCRT-III membrane-remodelling superfamily, Cell, Vol: 184, Pages: 3660-3673.e18, ISSN: 0092-8674
Membrane remodeling and repair are essential for all cells. Proteins that perform these functions include Vipp1/IM30 in photosynthetic plastids, PspA in bacteria, and ESCRT-III in eukaryotes. Here, using a combination of evolutionary and structural analyses, we show that these protein families are homologous and share a common ancient evolutionary origin that likely predates the last universal common ancestor. This homology is evident in cryo-electron microscopy structures of Vipp1 rings from the cyanobacterium Nostoc punctiforme presented over a range of symmetries. Each ring is assembled from rungs that stack and progressively tilt to form dome-shaped curvature. Assembly is facilitated by hinges in the Vipp1 monomer, similar to those in ESCRT-III proteins, which allow the formation of flexible polymers. Rings have an inner lumen that is able to bind and deform membranes. Collectively, these data suggest conserved mechanistic principles that underlie Vipp1, PspA, and ESCRT-III-dependent membrane remodeling across all domains of life.
Naskar S, Hohl M, Tassinari M, et al., 2020, The structure and mechanism of the bacterial type II secretion system, Molecular Microbiology, Vol: 115, Pages: 412-424, ISSN: 0950-382X
The type II secretion system (T2SS) is a multi-protein complex used by many bacteria to move substrates across their cell membrane. Substrates released into the environment serve as local and long-range effectors that promote nutrient acquisition, biofilm formation, and pathogenicity. In both animals and plants, the T2SS is increasingly recognized as a key driver of virulence. The T2SS spans the bacterial cell envelope and extrudes substrates through an outer membrane secretin channel using a pseudopilus. An inner membrane assembly platform and a cytoplasmic motor controls pseudopilus assembly. This microreview focuses on the structure and mechanism of the T2SS. Advances in cryo-electron microscopy are enabling increasingly elaborate sub-complexes to be resolved. However, key questions remain regarding the mechanism of pseudopilus extension and retraction, and how this is coupled with the choreography of the substrate moving through the secretion system. The T2SS is part of an ancient type IV filament superfamily that may have been present within the last universal common ancestor (LUCA). Overall, mechanistic principles that underlie T2SS function have implication for other closely related systems such as the type IV and tight adherence pilus systems.
Chernyatina A, Low H, 2019, Core architecture of a bacterial type II secretion system, Nature Communications, Vol: 10, ISSN: 2041-1723
Bacterial type II secretion systems (T2SSs) translocate virulence factors, toxins and enzymes across the cell outer membrane. Here we use negative stain and cryo-electron microscopy to reveal the core architecture of an assembled T2SS from the pathogen Klebsiella pneumoniae. We show that 7 proteins form a ~2.4 MDa complex that spans the cell envelope. The outer membrane complex includes the secretin PulD, with all domains modelled, and the pilotin PulS. The inner membrane assembly platform components PulC, PulE, PulL, PulM and PulN have a relative stoichiometric ratio of 2:1:1:1:1. The PulE ATPase, PulL and PulM combine to form a flexible hexameric hub. Symmetry mismatch between the outer membrane complex and assembly platform is overcome by PulC linkers spanning the periplasm, with PulC HR domains binding independently at the secretin base. Our results show that the T2SS has a highly dynamic modular architecture, with implication for pseudo-pilus assembly and substrate loading.
Liu J, Noel J, Low HH, 2018, Structural basis for membrane tethering by a bacterial dynamin-like pair, Nature Communications, Vol: 9, Pages: 1-12, ISSN: 2041-1723
Dynamin-like proteins (DLPs) are large GTPases that restructure membrane. DLPs such as the mitofusins form heterotypic oligomers between isoform pairs that bridge and fuse opposing membranes. In bacteria, heterotypic oligomerisation may also be important for membrane remodelling as most DLP genes are paired within operons. How DLPs tether opposing membranes is unknown. Here we show the crystal structure of a DLP heterotypic pair from the pathogen Campylobacter jejuni. A 2:2 stoichiometric tetramer is observed where heterodimers, conjoined by a random coil linker, assemble back-to-back to form a tripartite DLP chain with extreme flexibility. In vitro, tetramerisation triggers GTPase activity and induces lipid binding. Liposomes are readily tethered and form tubes at high tetramer concentration. Our results provide a direct mechanism for the long-range binding and bridging of opposing membranes by a bacterial DLP pair. They also provide broad mechanistic and structural insights that are relevant to other heterotypic DLP complexes.
Bohuszewicz O, Low HH, 2018, Structure of a mitochondrial fission dynamin in the closed conformation, Nature Structural and Molecular Biology, Vol: 25, Pages: 722-731, ISSN: 1545-9985
Dynamin 1-like proteins (DNM1-L) are mechanochemical GTPases that induce membrane fission in mitochondria and peroxisomes. Their mechanism depends on conformational changes driven by nucleotide and lipid cycling. Here we show the crystal structure of a mitochondrial fission dynamin (CmDnm1) from the algae Cyanidioschyzon merolae. Unlike other eukaryotic dynamin structures, CmDnm1 is in a hinge 1 closed conformation, with the GTPase domain compacted against the stalk. Within the crystal, CmDnm1 packs as a diamond-shaped tetramer that is consistent with an inactive off-membrane state. Crosslinking, photoinduced electron transfer assays, and electron microscopy verify these structures. In vitro, CmDnm1 forms concentration-dependent rings and protein–lipid tubes reminiscent of DNM1-L and classical dynamin with hinge 1 open. Our data provides a mechanism for filament collapse and membrane release that may extend to other dynamin family members. Additionally, hinge 1 closing may represent a key conformational change that contributes to membrane fission.
Antonny B, Burd C, De Camilli P, et al., 2016, Membrane fission by dynamin: what we know and what we need to know, EMBO Journal, Vol: 35, Pages: 1957-2060, ISSN: 0261-4189
The large GTPase dynamin is the first protein shown to catalyze membrane fission. Dynamin and its related proteins are essential to many cell functions, from endocytosis to organelle division and fusion, and it plays a critical role in many physiological functions such as synaptic transmission and muscle contraction. Research of the past three decades has focused on understanding how dynamin works. In this review, we present the basis for an emerging consensus on how dynamin functions. Three properties of dynamin are strongly supported by experimental data: first, dynamin oligomerizes into a helical polymer; second, dynamin oligomer constricts in the presence of GTP; and third, dynamin catalyzes membrane fission upon GTP hydrolysis. We present the two current models for fission, essentially diverging in how GTP energy is spent. We further discuss how future research might solve the remaining open questions presently under discussion.
Bohuszewicz O, Liu J, Low HH, 2016, Membrane remodelling in bacteria, Journal of Structural Biology, Vol: 196, Pages: 3-14, ISSN: 1095-8657
In bacteria the ability to remodel membrane underpins basic cell processes such as growth, and more sophisticated adaptations like inter-cell crosstalk, organelle specialisation, and pathogenesis. Here, selected examples of membrane remodelling in bacteria are presented and the diverse mechanisms for inducing membrane fission, fusion, and curvature discussed. Compared to eukaryotes, relatively few curvature-inducing proteins have been characterised so far. Whilst it is likely that many such proteins remain to be discovered, it also reflects the importance of alternative membrane remodelling strategies in bacteria where passive mechanisms for generating curvature are utilised.
Michie KA, Boysen A, Low HH, et al., 2014, LeoA, B and C from enterotoxigenic escherichia coli (ETEC) are bacterial dynamins, PLoS One, Vol: 9, Pages: 1-10, ISSN: 1932-6203
Escherichia coli (ETEC) strain H10407 contains a GTPase virulence factor, LeoA, which is encoded on a pathogenicity island and has been shown to enhance toxin release, potentially through vesicle secretion. By sequence comparisons and X-ray structure determination we now identify LeoA as a bacterial dynamin-like protein (DLP). Proteins of the dynamin family remodel membranes and were once thought to be restricted to eukaryotes. In ETEC H10407 LeoA localises to the periplasm where it forms a punctate localisation pattern. Bioinformatic analyses of leoA and the two upstream genes leoB and leoC suggest that LeoA works in concert with a second dynamin-like protein, made up of LeoB and LeoC. Disruption of the leoAB genes leads to a reduction in secretion of periplasmic Tat-GFP and outer membrane OmpA. Our data suggest a role for LeoABC dynamin-like proteins in potentiating virulence through membrane vesicle associated toxin secretion.
Low HH, Gubellini F, Rivera-Calzada A, et al., 2014, Structure of a Type IV secretion system, Nature, Vol: 508, Pages: 550-553, ISSN: 0028-0836
Bacterial type IV secretion systems translocate virulence factors into eukaryotic cells1,2, distribute genetic material between bacteria and have shown potential as a tool for the genetic modification of human cells3. Given the complex choreography of the substrate through the secretion apparatus4, the molecular mechanism of the type IV secretion system has proved difficult to dissect in the absence of structural data for the entire machinery. Here we use electron microscopy to reconstruct the type IV secretion system encoded by the Escherichia coli R388 conjugative plasmid. We show that eight proteins assemble in an intricate stoichiometric relationship to form an approximately 3 megadalton nanomachine that spans the entire cell envelope. The structure comprises an outer membrane-associated core complex1 connected by a central stalk to a substantial inner membrane complex that is dominated by a battery of 12 VirB4 ATPase subunits organized as side-by-side hexameric barrels. Our results show a secretion system with markedly different architecture, and consequently mechanism, to other known bacterial secretion systems1,4,5,6.
Low HH, Loewe J, 2010, Dynamin architecture - from monomer to polymer, CURRENT OPINION IN STRUCTURAL BIOLOGY, Vol: 20, Pages: 791-798, ISSN: 0959-440X
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- Citations: 31
Low HH, Sachse C, Amos LA, et al., 2009, Structure of a Bacterial Dynamin-like Protein Lipid Tube Provides a Mechanism For Assembly and Membrane Curving, CELL, Vol: 139, Pages: 1342-1352, ISSN: 0092-8674
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- Citations: 136
Low HH, Loewe J, 2006, A bacterial dynamin-like protein, NATURE, Vol: 444, Pages: 766-769, ISSN: 0028-0836
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- Citations: 176
Low HH, Moncrieffe MC, Löwe J, 2004, The crystal structure of ZapA and its modulation of FtsZ polymerisation, JOURNAL OF MOLECULAR BIOLOGY, Vol: 341, Pages: 839-852, ISSN: 0022-2836
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- Citations: 110
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