Recombinant Marinobacter aquaeolei ATP synthase subunit b (atpF)

How does recombinant Marinobacter aquaeolei ATP synthase subunit b compare to the native protein?

Recombinant Marinobacter aquaeolei ATP synthase subunit b differs from the native protein in several key aspects:

• Expression system: The recombinant protein is produced in heterologous systems like E. coli or yeast expression systems rather than the native organism

• Protein tags: Typically includes affinity tags (such as N-terminal 10xHis-tag) to facilitate purification

• Production format: Available as liquid or lyophilized powder with specific buffer components

• Potential modifications: May contain additional linker sequences between tags and the target protein

These differences must be considered when designing experiments, as they may affect protein folding, stability, and functionality compared to the native form. When selecting a recombinant form, researchers should evaluate whether these modifications might impact their specific experimental objectives.

What expression systems are used for producing recombinant Marinobacter aquaeolei ATP synthase subunit b?

Multiple expression systems are utilized for producing recombinant Marinobacter aquaeolei ATP synthase subunit b, each with specific advantages:

The search results indicate that recombinant Marinobacter aquaeolei ATP synthase subunit b is commercially available from multiple expression systems, including E. coli and yeast . For in vitro studies, E. coli expression systems appear to be commonly used, likely due to the balance between yield and functionality for this particular protein .

How does ATP synthase subunit b contribute to the rotary mechanism of ATP synthesis?

ATP synthase subunit b serves critical mechanical roles in the rotary mechanism of ATP synthesis through several key contributions:

First, it forms part of the peripheral stalk (stator) that prevents the α3β3 hexamer from rotating with the central stalk during catalysis . This counter-force is essential for the "binding-change" mechanism first proposed by Boyer, which explains how ATP is synthesized at the catalytic sites located at the interface between α and β subunits .

Second, recent structural studies have revealed that the peripheral stalk, including subunit b, exhibits elastic deformation during catalysis . This research demonstrates that during ATP hydrolysis, the peripheral stalk undergoes significant bending, storing mechanical energy that can later be released to drive the relative rotation needed for ATP synthesis . This elastic deformation reveals how mechanical strain in the stalk might accumulate during proton translocation and then be released to drive the rotor through sub-steps within F1, leading to catalysis .

Third, the peripheral stalk helps maintain proper alignment between the F1 and Fo domains, ensuring efficient coupling between proton translocation and ATP synthesis . This alignment is crucial for maintaining the tight coupling between proton movement and ATP production that characterizes ATP synthase operation.

As noted in the study by Iino et al., only the N-terminal helix of subunit γ together with subunit δ in an upward position is necessary to catalyze ATP synthesis, highlighting the remarkable engineering efficiency of this molecular machine .

What methodologies are optimal for studying interactions between recombinant ATP synthase subunit b and other complex components?

Studying the interactions between recombinant ATP synthase subunit b and other components requires specialized approaches due to the challenges of working with membrane proteins:

1. Membrane-Mimetic Systems:

• Nanodiscs or liposomes provide native-like lipid bilayer environments for reconstitution studies

• Detergent micelles can be used for initial solubilization but may affect native interactions

2. Structural Analysis Techniques:

• Cryo-electron microscopy (cryo-EM) has emerged as the method of choice for visualizing ATP synthase complexes in different functional states

• X-ray crystallography has been successfully applied to subcomponents like the F1 domain

• Hydrogen-deuterium exchange mass spectrometry (HDX-MS) can map interaction interfaces

3. Functional Reconstitution:

• Reconstitution of purified components into liposomes allows assessment of ATP synthesis or hydrolysis activities

• Measuring proton flux through reconstituted complexes can evaluate the coupling efficiency

• Electric pulse techniques can be used to generate membrane potential for functional studies

4. Interaction Validation:

• Crosslinking followed by mass spectrometry analysis can identify proximity relationships

• Pull-down assays using tagged recombinant subunit b can identify binding partners

• Blue native PAGE can assess complex assembly and stability

Recent advances in cryo-EM have been particularly valuable, allowing researchers to visualize ATP synthase in different catalytic states and under various conditions, as demonstrated in studies of mycobacterial and yeast ATP synthases .

How do mutations in ATP synthase subunit b affect complex assembly and function?

Mutations in ATP synthase subunit b can have profound effects on complex assembly and function through several mechanisms:

Impacts on Assembly:

• Peripheral stalk stability is critical for the assembly of the complete ATP synthase complex

• Studies in yeast have shown that the peripheral stalk, including subunit b equivalents, provides a physical link between the proton channel and other stator components

• Mutations affecting the interaction between subunit b and other stator components can disrupt proper assembly sequence

Functional Consequences:

• Alterations in the elastic properties of subunit b can affect energy storage and transfer during catalysis

• Changes in the peripheral stalk structure may impact the coupling efficiency between proton translocation and ATP synthesis

• Mutations affecting the interaction with subunit a could disrupt proton channeling mechanisms

Research in mycobacterial ATP synthase has identified specific mechanisms of auto-inhibition involving interactions between the peripheral stalk and other components . This suggests that precise structural relationships between subunit b and other parts of the complex are essential for proper regulation.

The "fail-safe" mechanism described in mycobacterial ATP synthase involving the b′-subunit in the peripheral stalk highlights how critical these interactions are for controlling ATP hydrolysis . Similar regulatory mechanisms might exist in Marinobacter aquaeolei ATP synthase, though specific studies would be needed to confirm this.

How does the ATP synthase rotor-stator interaction mechanism relate to subunit b function?

The interaction between the rotor and stator components of ATP synthase is fundamental to its function, with subunit b playing a crucial role in this mechanism:

Structural Basis:

• ATP synthase can be mechanically divided into "rotor" (c-ring, γ, δ, ε) and "stator" (α3β3, a, b, d, F6, OSCP) components

• Subunit b forms part of the stator framework that resists the torque generated during rotation

• Recent cryo-EM studies have revealed that the peripheral stalk undergoes significant deformation during catalysis, storing mechanical energy

Mechanistic Implications:

• The proton motive force (pmf) is delivered directly and tangentially to the rotor via a Grotthuss water chain in a polar L-shaped tunnel

• This generates rotational force that is opposed by the peripheral stalk, including subunit b

• The elastic deformation of the peripheral stalk during rotation suggests it functions as a molecular spring

Functional Coupling:

• Tight coupling between proton translocation and ATP synthesis requires the unique rotational mechanism of ATP synthase

• The peripheral stalk ensures that the α3β3 hexamer remains fixed relative to subunit a during catalysis

• Under certain pathophysiological conditions, ATP synthase can run in reverse, with the stator components maintaining the same structural relationships

A recent study of yeast mitochondrial ATP synthase under strain during ATP-hydrolysis-driven rotary catalysis revealed large deformations of the peripheral stalk . This suggests that during ATP synthesis, proton translocation causes accumulation of strain in the stalk, which then relaxes by driving rotation of the rotor through sub-steps within F1, leading to catalysis .

What role does ATP synthase subunit b play in mitochondrial permeability transition pore formation?

Recent research has implicated ATP synthase, including components of the peripheral stalk, in the formation of the mitochondrial permeability transition pore (mPTP):

Evidence for ATP Synthase as mPTP:

• Multiple studies have suggested that ATP synthase houses the channel of mPTP

• Specific interaction between ATP synthase OSCP subunit and cyclophilin D (CypD), a known regulator of mPTP, has been described

• Uncoupling of proton translocation and ATP synthesis, along with other cellular malfunctions, can trigger mPTP opening

Potential Role of Subunit b:

• As part of the peripheral stalk, subunit b likely contributes to the structural rearrangements associated with mPTP formation

• Changes in subunit b conformation could affect the stability of interfaces between ATP synthase components

• Structural stress transmitted through subunit b might contribute to conformational changes leading to pore formation

Pathological Implications:

• mPTP opening is associated with various pathologies including neurodegeneration

• Targeting specific interactions involving peripheral stalk components could potentially modulate mPTP formation

• Understanding the role of subunit b in this process could lead to new therapeutic strategies

While most studies on mPTP have focused on mitochondrial ATP synthases rather than bacterial homologs, the structural and functional insights gained from studying Marinobacter aquaeolei ATP synthase subunit b could contribute to our understanding of the fundamental mechanisms involved in this process.

What techniques can assess the proper folding and functionality of recombinant ATP synthase subunit b?

Assessing proper folding and functionality of recombinant ATP synthase subunit b requires a multi-faceted approach:

Structural Integrity Assessment:

Functional Validation:

• Integration into reconstituted ATP synthase complexes

• ATP synthesis/hydrolysis assays with reconstituted complexes

• Proton translocation measurements in liposomes

• Assembly assays using Blue Native PAGE

Interaction Studies:

• Pull-down assays with other ATP synthase components

• Surface plasmon resonance to quantify binding kinetics

• Isothermal titration calorimetry for thermodynamic parameters

• Crosslinking mass spectrometry to identify interaction interfaces

Structural Verification:

• Negative stain electron microscopy for initial complex assessment

• Cryo-EM for high-resolution structural determination

• Hydrogen-deuterium exchange mass spectrometry for conformational analysis

The combination of these approaches provides comprehensive validation of recombinant protein quality before proceeding to detailed structural or functional studies.