Bacterial Actins and Their Diversity

Ozyamak, Ertan; Kollman, Justin M.; Komeili, Arash

doi:10.1021/bi4010792

Cited by 40 publications

(37 citation statements)

References 97 publications

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“…Various studies proved the existence of bacterial homologs of eukaryotic cytoskeleton proteins including tubulin homologs such as FtsZ (1), actin homologs such as MreB (2), and intermediate filament (IF)-like proteins (3), which together have important roles in cell division, morphogenesis, polarity determination, and DNA segregation (4)(5)(6)(7). In addition, several groups of polymer-forming proteins that are limited to the bacterial domain have been described (6).…”

mentioning

confidence: 99%

β-Helical architecture of cytoskeletal bactofilin filaments revealed by solid-state NMR

Vasa¹,

Lin

Shi

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Bactofilins are a widespread class of bacterial filament-forming proteins, which serve as cytoskeletal scaffolds in various cellular pathways. They are characterized by a conserved architecture, featuring a central conserved domain (DUF583) that is flanked by variable terminal regions. Here, we present a detailed investigation of bactofilin filaments from Caulobacter crescentus by highresolution solid-state NMR spectroscopy. De novo sequential resonance assignments were obtained for residues Ala39 to Phe137, spanning the conserved DUF583 domain. Analysis of the secondary chemical shifts shows that this core region adopts predominantly β-sheet secondary structure. Mutational studies of conserved hydrophobic residues located in the identified β-strand segments suggest that bactofilin folding and polymerization is mediated by an extensive and redundant network of hydrophobic interactions, consistent with the high intrinsic stability of bactofilin polymers. Transmission electron microscopy revealed a propensity of bactofilin to form filament bundles as well as sheet-like, 2D crystalline assemblies, which may represent the supramolecular arrangement of bactofilin in the native context. Based on the diffraction pattern of these 2D crystalline assemblies, scanning transmission electron microscopy measurements of the mass per length of BacA filaments, and the distribution of β-strand segments identified by solid-state NMR, we propose that the DUF583 domain adopts a β-helical architecture, in which 18 β-strand segments are arranged in six consecutive windings of a β-helix.solid-state NMR | cytoskeleton | protein structure | filaments

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confidence: 99%

β-Helical architecture of cytoskeletal bactofilin filaments revealed by solid-state NMR

Vasa¹,

Lin

Shi

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…The bacterial actin superfamily contains numerous phylogenetically distinct subgroups (6,7), each of which includes members that participate in specialized functions such as cell shape determination (8)(9)(10), motility (11), DNA segregation (12)(13)(14), and cytokinesis (15,16). High-resolution imaging of AMB-1 cells by electron cryotomography (ECT) shows that magnetosomes are flanked by filamentous structures (17).…”

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confidence: 99%

Interplay between Two Bacterial Actin Homologs, MamK and MamK-Like, Is Required for the Alignment of Magnetosome Organelles in Magnetospirillum magneticum AMB-1

et al. 2014

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dMany bacterial species contain multiple actin-like proteins tasked with the execution of crucial cell biological functions. MamK, an actin-like protein found in magnetotactic bacteria, is important in organizing magnetosome organelles into chains that are used for navigation along geomagnetic fields. MamK and numerous other magnetosome formation factors are encoded by a genetic island termed the magnetosome island. Unlike most magnetotactic bacteria, Magnetospirillum magneticum AMB-1 (AMB-1) contains a second island of magnetosome-related genes that was named the magnetosome islet. A homologous copy of mamK, mamK-like, resides within this islet and encodes a protein capable of filament formation in vitro. Previous work had shown that mamK-like is expressed in vivo, but its function, if any, had remained unknown. Though MamK-like is highly similar to MamK, it contains a mutation that in MamK and other actins blocks ATPase activity in vitro and filament dynamics in vivo. Here, using genetic analysis, we demonstrate that mamK-like has an in vivo role in assisting organelle alignment. In addition, MamK-like forms filaments in vivo in a manner that is dependent on the presence of MamK and the two proteins interact in a yeast two-hybrid assay. Surprisingly, despite the ATPase active-site mutation, MamK-like is capable of ATP hydrolysis in vitro and promotes MamK filament turnover in vivo. Taken together, these experiments suggest that direct interactions between MamK and MamK-like contribute to magnetosome alignment in AMB-1.

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“…Symmetry constraints mean that in a double-helical filament the subunits from each of the two strands can only be either staggered or juxtaposed (in-register) without creating chemically different strands. Actin and most other actin-like filaments show staggered filaments (20), possibly because such an arrangement produces ends that are not blunt, helping with filament elongation and nucleation. MreB also forms juxtaposed filaments but they are nonpolar, antiparallel, and not helical (12).…”

Section: Resultsmentioning

confidence: 99%

X-ray and cryo-EM structures of monomeric and filamentous actin-like protein MamK reveal changes associated with polymerization

Löwe

Scheres

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Magnetotactic bacteria produce iron-rich magnetic nanoparticles that are enclosed by membrane invaginations to form magnetosomes so they are able to sense and act upon Earth's magnetic field. In Magnetospirillum and other magnetotactic bacteria, to combine their magnetic moments, magnetosomes align along filaments formed by a bacterial actin homolog, MamK. Here, we present the crystal structure of a nonpolymerizing mutant of MamK from Magnetospirillum magneticum AMB-1 at 1.8-Å resolution, revealing its close similarity to actin and MreB. The crystals contain AMPPNPbound monomeric MamK in two different conformations. To investigate conformational changes associated with polymerization, we used unmodified MamK protein and cryo-EM with helical 3D reconstruction in RELION to obtain a density map and a fully refined atomic model of MamK in filamentous form at 3.6-Å resolution. The filament is parallel (polar) double-helical, with a rise of 52.2 Å and a twist of 23.8°. As shown previously and unusually for actin-like filaments, the MamK subunits from each of the two strands are juxtaposed, creating an additional twofold axis along the filament. Compared with monomeric MamK, ADP-bound MamK in the filament undergoes a conformational change, rotating domains I and II against each other to further close the interdomain cleft between subdomains IB and IIB. The domain movement causes several loops to close around the nucleotide-binding pocket. Glu-143, a key residue for catalysis coordinating the magnesium ion, moves closer, presumably switching nucleotide hydrolysis upon polymerization-one of the hallmarks of cytomotive filaments of the actin type.magnetotactic bacteria | magnetosomes | filamentous proteins | bacterial cytoskeleton | cryo-EM I t was discovered in 1975 by Richard Blakemore that certain bacteria sense magnetic fields and swim according to the field's direction (1). The cells contain specialized iron-rich, membranebounded organelles, magnetosomes (2, 3). Magnetosomes contain magnetic nanoparticles that either together confer a magnetic moment to the bacterium or produce a signal that is used by the bacterium's chemotaxis machinery to swim in a particular direction.Magnetosomes occur in many different bacteria, but have been studied in some detail in gram-negative Magnetospirillum gryphiswaldense and Magnetospirillum magneticum AMB-1. In these organisms, typically 10 to 20 magnetosomes form as invaginations of the inner membrane, meaning that the nanoparticles are outside of the inner membrane, in the periplasm (4). They align along a straight line, into a chain, along the inner perimeter of the helical cells. Biomineralization and membrane invagination are somewhat coupled, although first empty or almost empty membrane invaginations form (5).In Magnetospirillum, magnetosome formation is encoded in gene clusters, included in a large magnetosome island. Many genes are required because the process of magnetosome formation is complex, requiring iron uptake, iron transport, biomineralization, membrane enclosure, m...

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Bacterial Actins and Their Diversity

Cited by 40 publications

References 97 publications

β-Helical architecture of cytoskeletal bactofilin filaments revealed by solid-state NMR

β-Helical architecture of cytoskeletal bactofilin filaments revealed by solid-state NMR

Interplay between Two Bacterial Actin Homologs, MamK and MamK-Like, Is Required for the Alignment of Magnetosome Organelles in Magnetospirillum magneticum AMB-1

X-ray and cryo-EM structures of monomeric and filamentous actin-like protein MamK reveal changes associated with polymerization

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