Name: bacterial cytoskeleton and cell shape
Uploaded: 2023-04-30T09:30:58.000Z
Duration: 1 min 29 s
Channel: JoVE

Bacterial cells have diverse cytoskeletal proteins including eukaryotic homologs of actin, tubulin, and intermediate filaments, along with a unique fourth group, the MinD-ParA proteins.
Actin homologs, MreB and Mbl are found abundantly in rod and spiral-shaped bacteria. These proteins form spiral scaffolds that guide the formation of the peptidoglycan cell wall.
Another actin homolog, ParM, is encoded by non-genomic antibiotic-resistant plasmids in some bacteria and spontaneously assembles into filaments.
During cell division, the growing filament polymers push the plasmid copies apart to the opposite ends of the cell.
Tubulin homologs, FtsZ and BtubA/B, polymerize into filaments or rings.
FtsZ filaments assemble into the Z-ring at the middle of the cell to initiate cell division.
Crescentin subunits are the only intermediate filament-like proteins identified in bacteria. They create a crescent shape in some bacteria like Caulobacter crescentus. In the absence of crescentin subunits, these bacteria turn rod-shaped.
MinD and ParA are ATPases unique to bacterial cells and are required for cell division.

cytoskeletal proteins in bacteria

Cytoskeletal Proteins in Bacteria

Bacterial cells were initially considered simple, randomly organized structures lacking a cytoskeleton. However, the discovery of cytoskeleton homologs in bacteria led to the change of this opinion. Bacterial cytoskeletal filaments regulate the cell shape, cell polarity, cell division, and partitioning of plasmids during cell division. It was later discovered that bacterial cytoskeletal proteins, mainly actin and tubulin homologs, are diverse compared to their eukaryotic counterparts. On the other hand, intermediate filaments are extremely rare, with only a single homolog Crescentin, being reported.
Bacterial Actin
Bacterial actins, as per their gene sequences, are known to be highly diverse. They are classified into distinct families based on phylogenetic analysis, structural features, and functional similarities. Bioinformatics analysis has led to the classification of up to 35 different families of bacterial actin. Structural variations in bacterial actin filaments include&#8212;a dramatic change in the twist, where the intersubunit angles vary by around +/- 10o in a filament; changes in strand number; and the possibility of antiparallel strands. These differences in filament structure ultimately lead to differences in filament dynamics and, thereby, their function. Despite their diversity, the important point is that the individual subunits have a similar tertiary structure and evolved from the same ancestor as eukaryotic actins.
Bacterial Tubulin
Microtubules formed from bacterial tubulin-like proteins are structurally different from the 13 protofilament structure common amongst most eukaryotes. Bacterial tubulins like FtsZ are known to form single-stranded filaments or twisted filament pairs instead of hollow tubes. Other homologs like BtubA/BtubB, mainly found in Prosthecobacter species, include a 5-protofilament structure. Although discovered later, it is hypothesized that bacterial microtubules came before the 13-protofilament eukaryotic structure, and longitudinal bonds in single-stranded filaments evolved before the lateral interaction required for the protofilament structure. And with the 5-protofilament structure found in Prosthecobacter species, the only reported bacterial protofilament is hypothesized to be an outcome of horizontal gene transfer.

Bacterial cells were initially considered simple, randomly organized structures lacking a cytoskeleton. However, the discovery of cytoskeleton homologs in ...

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JoVE Core

Cell Biology

Unit 1

The Cytoskeleton I: Actin and Microfilaments

the-cytoskeleton-i-actin-and-microfilaments

KEY TERMS AND CONCEPTS

bacterial cytoskeleton and cell shape

Bacterial cytoskeletal proteins help bacteria keep their shape and divide correctly. They also help set cell polarity and move plasmids, which are small DNA circles, into place during cell division. Bacteria were once thought to be simple and randomly organized, but the discovery of cytoskeleton homologs changed that view.

The main bacterial cytoskeletal proteins are actin-like and tubulin-like proteins. These proteins are more diverse in bacteria than in eukaryotic cells, and intermediate filaments are very rare. Only one intermediate filament homolog, Crescentin, has been reported so far.

Bacterial actins are especially diverse at the gene level. They are grouped into separate families by phylogenetic analysis, structure, and function, and bioinformatics has identified up to 35 actin families. Their filaments can differ in twist, strand number, and even strand direction, including the possibility of antiparallel strands. These structural changes affect filament dynamics and therefore their function.

Even with this diversity, bacterial actin subunits share a similar tertiary structure. They also likely came from the same ancestor as eukaryotic actins. Bacterial tubulin-like proteins show a different pattern. FtsZ can form single-stranded filaments or twisted filament pairs instead of the hollow 13-protofilament tubes seen in most eukaryotic microtubules.

Other tubulin homologs, such as BtubA and BtubB in Prosthecobacter species, form a 5-protofilament structure. Researchers have suggested that bacterial microtubules may have appeared before the 13-protofilament eukaryotic form. They also propose that longitudinal bonds in single-stranded filaments came before the lateral interactions needed for the fuller protofilament structure. The 5-protofilament form in Prosthecobacter is also thought to be the result of horizontal gene transfer.

Bacterial Cytoskeleton and Cell Shape

introduction to the cytoskeleton

Cytoskeleton Structure and Cell Movement

The cytoskeleton is a network of protein filaments inside the cell. It gives cells shape, helps organize cell contents, and supports movement. Although the name suggests a fixed skeleton, it is a dynamic structure that can change quickly in response to signals or forces. Three main filament types make up the cytoskeleton: microfilaments, microtubules, and intermediate filaments. Each one has different assembly and disassembly behavior, mechanical strength, polarity, and associated motor...

adaptability of cytoskeletal filaments

Cytoskeletal Filaments in Cell Movement

Cytoskeletal filaments help cells change shape, divide, and move. Their flexibility lets them stay stable for hours during interphase or reorganize quickly during cell division. Strong regulation controls how these filaments assemble, fall apart, and form networks. Microfilaments and microtubules are dynamic, while intermediate filaments are considered more static. Microfilaments are spread throughout the cell body and can shift into different structures. Many proteins in the cell, including...

polarity of the cytoskeleton

How Cytoskeleton Polarity Guides Cell Movement

Cell polarity depends on the organization of the cytoskeleton and the uneven placement of cell parts. Two main factors help create this polarity. Mobile components such as regulatory molecules and subcellular structures can collect more on one side of the cell. Polar cytoskeletal filaments also line up along the cell’s axis of polarity. The interactions between cytoskeletal filaments help build and maintain this polarized shape. Several features also matter. These include the structure of the...

assembly of cytoskeletal filaments

Actin Bundles and Microtubule Cylinders

Cytoskeletal filaments are built from smaller protein subunits, but they can also join with similar filaments to form stronger cell structures. Microfilaments, which are made of actin monomers, depend on actin-binding proteins to form bundles and networks. Microtubules use microtubule-associated proteins, or MAPs, to form sturdy cylindrical structures. The protein partners for rope-like intermediate filament structures are still unknown. Actin bundles can be compact or loosely spaced. Compact...

cytoskeletal linker proteins - plakins

Plakins in Cell Junctions and Disease

Plakins are large cytoskeletal linker proteins that connect microtubules, microfilaments, intermediate filaments, and membrane protein complexes at cell junctions. They help organize the cytoskeleton by crosslinking its parts and by linking them to the cell matrix and cell adhesion complexes. These proteins also do more than provide structure. Plakins can interact with signal transducers, act as scaffolds for signaling complexes, and help control vesicle trafficking. They were first found with...

cytoskeletal accessory proteins

How Accessory Proteins Support the Cytoskeleton

Accessory proteins help the cytoskeleton work as a connected system. The cytoskeleton is a key cell structure with both structural and functional roles. Its filaments do not work well on their own, so accessory proteins assist with filament formation, stability, and function. These proteins also support communication between cytoskeletal filaments. They are found in both prokaryotes and eukaryotes, although bacterial accessory proteins differ a lot from one species to another. The evolutionary...

Bacterial cytoskeletal proteins help bacteria keep their shape and divide correctly. They also help set cell polarity and move plasmids, which are small DNA circles, into place during cell division. Bacteria were once thought to be simple and randomly organized, but the discovery of cytoskeleton homologs changed that view. The main bacterial cytoskeletal proteins are actin-like and tubulin-like proteins. These proteins are more diverse in bacteria than in eukaryotic cells, and intermediate...

intracellular movement of viruses and bacteria

intracellular-movement-of-viruses-and-bacteria

How Viruses and Bacteria Ride the Cytoskeleton

Intracellular bacteria and viruses use the host cell cytoskeleton to move inside and between cells. These pathogens can travel from the cell surface to the nuclear region and back again. They may also spread across cells through cortical protrusions, which are cell membrane extensions at the edge of the cell. Several infectious agents use this strategy. Bacterial examples include Rickettsia, which can cause Rocky Mountain spotted fever and Mediterranean spotted fever, Chlamydia, which causes a...

studying the cytoskeleton

Visualizing Cytoskeleton Structure and Motion

The cytoskeleton can be studied with microscopy and biochemical methods. Electron microscopy helped reveal its architecture in the 1960s. It gives very high-resolution structural detail, but sample preparation can limit what is seen in biological samples. One electron microscopy method is rotary shadowing, also called metal replica. In this protocol, cytoskeletal filaments are fixed with chemicals such as glutaraldehyde or formaldehyde. The sample is then dehydrated with alcohol to a critical...

introduction to actin

Actin Structure, Isoforms, and Roles

Actin is a major cytoskeletal protein in eukaryotic cells. In muscle cells, it can make up about 10% of the total cellular protein. In non-muscle cells, it is lower and usually makes up around 1 to 5 percent of total cell protein. Actin is also highly conserved, which means it has changed very little over time. Actin in unicellular amoebae and in complex multicellular animals is about 80% similar. Actin genes are also conserved within a species and across different species. For example, actin...

actin polymerization

Actin Filament Growth Stages

Actin filament growth starts when G-actin, or monomeric actin, links together to form F-actin, the filament form. This process builds the actin network in cells through head-to-tail binding between actin subunits. It moves through three stages: nucleation, elongation, and the steady-state phase. Nucleation is the first and hardest step. During this phase, three actin monomers come together to form a stable nucleus. That nucleus then serves as the start of a new actin filament. After...

actin treadmilling

Actin Filament Growth and Loss

Actin filaments grow and shrink at the same time in a process called treadmilling. In this process, G-actin monomers are added at one end of the filament and removed from the other end. The rate of each step depends on the amount of free G-actin in the cytosol, the fluid inside the cell. The plus end, also called the barbed end, usually adds actin faster. The minus end, also called the pointed end, usually loses actin faster. At steady state, the critical concentration is the level of free...

generation of straight or branched actin filaments

generation-of-straight-or-branched-actin-filaments

Actin Filament Branching and Straight Growth

Actin filaments can grow as either straight strands or branched networks. Two nucleating proteins control this shape choice: formins and the Arp2/3 complex. Formins build straight actin filaments, while the Arp2/3 complex builds branched ones. The Arp2/3 complex is made of seven subunits. Two of them, Arp2 and Arp3, are actin-like proteins, and five other subunits help keep them inactive until they are needed. Activation happens with help from other proteins called nucleation-promoting...

actin filament depolymerization

Actin Filament Breakdown at Cell Ends

Actin filaments are built from actin subunits, and they can break down from either end. This process is called depolymerization. It happens faster at the minus-end, also called the pointed end, where the subunits are usually in the ADP-actin form. Several proteins help speed up actin filament breakdown. The actin-depolymerizing factor, or ADF, and cofilin proteins bind to ADP-actin in a one-to-one ratio. When they bind, the filament twists, which creates stress and makes it brittle. That...

formation of higher-order actin filaments

formation-of-higher-order-actin-filaments

Actin Bundles and Cell Shape

Actin bundles and cross-links help shape cells by organizing F-actin into larger networks. G-actin monomers first polymerize into filamentous F-actin, and those filaments then assemble into higher-order structures that support cell function. These structures can help build lamellipodia and filopodia at the leading edge of a migrating cell. They also help form microvilli on the brush border of epithelial cells. Higher-order actin networks can form in two main ways. Straight F-actins may bundle...

overview of myosin structure and function

overview-of-myosin-structure-and-function

Myosin Types in Muscle and Cell Transport

Myosins are molecular motor proteins that help cells move materials and generate force. They were first identified in skeletal muscle, where they drive muscle contraction. They also help move molecules and vesicles inside cells. Myosin proteins are divided into 24 classes based on their domain sequence and organization. Six classes are especially well characterized: Myosin I, Myosin II, Myosin V, Myosin VI, Myosin VII, and Myosin X. These proteins also take part in contractile ring formation...

actin and myosin in muscle contraction

Sarcomere Structure in Skeletal Muscle

Sarcomere structure in skeletal muscle explains how actin and myosin help muscles contract. These contractile proteins are arranged in repeating units called sarcomeres, which are found in skeletal muscle tissue. Their repeated pattern gives skeletal muscle a striped, or striated, look under a microscope. The bands in a myofibril create this striped pattern. Dark A bands and light I bands repeat along the length of the myofibrils. When many myofibrils line up in a muscle cell, the whole cell...

the role of actin and myosin in non-muscle cells

the-role-of-actin-and-myosin-in-non-muscle-cells

How Actomyosin Bundles Shape Cell Movement

Actin and myosin form contractile bundles in non-muscle cells. These actomyosin structures help cells change shape, attach to surfaces, and divide. They were first observed in Dictyostelium and Acanthamoeba. Two common bundles are stress fibers and actomyosin adherence belts. These bundles are smaller and less organized than the ones found in muscle cells. Accessory proteins such as fascin, filamin, and fimbrin help hold them together, depending on where they are in the cell. Their formation...

key terms and concepts

Learn how bacterial actin and tubulin proteins support cell shape, division, polarity, and plasmid movement, plus how they differ from eukaryotic filaments.

Bacterial Cytoskeleton and Cell Shape | JoVE K12

cell biology

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Bacterial Cytoskeleton and Cell Shape

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