Recombinant Mannheimia succiniciproducens UPF0299 membrane protein MS1271 (MS1271)

What is MS1271 and what organism does it come from?

MS1271 is a membrane protein belonging to the UPF0299 family, found in Mannheimia succiniciproducens strain MBEL55E. M. succiniciproducens is a capnophilic (CO₂-loving), Gram-negative, facultative anaerobic bacterium originally isolated from bovine rumen. This organism has gained significant research interest due to its efficient production of succinic acid from various carbon sources, including pentose sugar (xylose), hexose sugars (fructose and glucose), and disaccharides (lactose, maltose, and sucrose) .

The designation "UPF0299" indicates that this protein family has an uncharacterized protein function, meaning its precise biological role remains to be fully elucidated. As a membrane protein, MS1271 is embedded within the bacterial cell membrane, which suggests potential roles in transport, signaling, or maintaining membrane integrity.

What are the structural characteristics of MS1271?

MS1271 is a relatively small membrane protein consisting of 144 amino acids with a molecular mass of 16.007 kDa . The protein belongs to the UPF0299 family, which is characterized by specific conserved sequence motifs and structural features.

Analysis of the amino acid sequence (MRQKIFLFVRSLIILYLILFIGEGIAKLIPIGIPGSIFGLLILFIGLTTQIIKVDWVFFGASLLIRYMAVLFVPVSVGVMKYSDLLVSHASSLLIPNIVSTCVTLLVIGFLGDYLFSLNSFTRLRKKAIKKRDINNVNNKGEAS) reveals a high proportion of hydrophobic residues, consistent with its membrane-embedded nature . This sequence suggests multiple potential transmembrane domains that anchor the protein within the bacterial membrane. The protein likely adopts an alpha-helical conformation within the membrane, which is common for integral membrane proteins.

How is recombinant MS1271 typically expressed and purified?

Recombinant MS1271 is typically expressed using an E. coli expression system. Based on commercial production methods, the gene encoding full-length MS1271 (amino acids 1-144) is cloned into an expression vector (such as pRSETA, similar to what was used for other Mannheimia proteins) , fused with an N-terminal His-tag to facilitate purification.

The expression methodology involves:

• Transformation of the expression construct into a suitable E. coli strain (such as BL21(DE3)pLysS)

• Induction of protein expression (typically using IPTG)

• Cell harvesting and lysis

• Purification via immobilized metal affinity chromatography (IMAC) using the His-tag

• Additional purification steps as needed (e.g., size exclusion chromatography)

• Lyophilization for stable storage

The purified protein typically achieves greater than 90% purity as determined by SDS-PAGE analysis .

What are the optimal storage conditions for recombinant MS1271?

The recommended storage conditions for recombinant MS1271 are:

• Long-term storage: Store the lyophilized powder at -20°C to -80°C upon receipt .

• Working aliquots: Store at 4°C for up to one week .

• Reconstitution: The protein should be reconstituted in deionized sterile water to a concentration of 0.1-1.0 mg/mL .

• To prevent protein degradation, the addition of 5-50% glycerol (final concentration) is recommended for aliquots intended for long-term storage at -20°C/-80°C .

• Avoid repeated freeze-thaw cycles as this may lead to protein denaturation and loss of activity .

The standard storage buffer consists of a Tris-based buffer with 6% Trehalose at pH 8.0 , though some commercial preparations may use a Tris-based buffer with 50% glycerol .

What is the predicted membrane topology of MS1271?

The membrane topology of MS1271 can be predicted based on its amino acid sequence using various bioinformatics tools (such as TMHMM, HMMTOP, or Phobius). Analysis of the sequence suggests multiple hydrophobic regions that likely form transmembrane helices.

The protein sequence (MRQKIFLFVRSLIILYLILFIGEGIAKLIPIGIPGSIFGLLILFIGLTTQIIKVDWVFFGASLLIRYMAVLFVPVSVGVMKYSDLLVSHASSLLIPNIVSTCVTLLVIGFLGDYLFSLNSFTRLRKKAIKKRDINNVNNKGEAS) contains several stretches of hydrophobic residues that potentially form transmembrane domains.

To experimentally validate these predictions, researchers could employ techniques such as:

• Cysteine scanning mutagenesis combined with accessibility assays

• Fusion reporter assays using reporter proteins like alkaline phosphatase or green fluorescent protein

• Epitope insertion and antibody accessibility studies

• Proteolytic digestion patterns of the membrane-embedded protein

These approaches would provide insight into which portions of the protein are exposed to the cytoplasm, periplasm, or embedded within the membrane.

How does MS1271 compare to other UPF0299 family proteins?

MS1271 belongs to the UPF0299 family of membrane proteins , a group of proteins that share sequence similarity but have limited functional characterization. To understand MS1271's relationship to other family members, researchers should:

• Perform multiple sequence alignments with other UPF0299 family members to identify:

  • Conserved residues that may indicate functional importance

  • Variable regions that might confer species-specific functions

  • Potential functional motifs

• Conduct phylogenetic analysis to determine evolutionary relationships among family members

• Compare predicted structural features with experimentally determined structures of related proteins (if available)

The UPF0299 family is distributed across various bacterial species, and comparative genomic analysis could provide insights into the conservation and potential functional importance of MS1271.

What potential roles might MS1271 play in Mannheimia succiniciproducens metabolism?

While the specific function of MS1271 has not been definitively characterized in the available literature, its nature as a membrane protein suggests several potential roles within M. succiniciproducens metabolism:

• Transport function: It may be involved in the transport of metabolites, ions, or nutrients essential for the organism's capnophilic lifestyle.

• Metabolic pathway involvement: Given M. succiniciproducens' efficient production of succinic acid, MS1271 could potentially be involved in CO₂ utilization or the transport of pathway intermediates. M. succiniciproducens utilizes several CO₂-fixing metabolic reactions for succinic acid production through pathways involving phosphoenolpyruvate carboxykinase, phosphoenolpyruvate carboxylase, and malic enzyme .

• Stress response: The protein might play a role in membrane integrity under various environmental conditions, particularly considering the organism's adaptation to the rumen environment.

To investigate these potential roles, researchers might employ:

• Gene knockout studies similar to those conducted for other genes in M. succiniciproducens

• Heterologous expression and functional complementation assays

• Metabolomic analysis comparing wild-type and MS1271-deficient strains

• Transcriptomic analysis to identify conditions under which MS1271 expression is regulated

What experimental approaches are recommended for functional characterization of MS1271?

For comprehensive functional characterization of MS1271, researchers should consider a multi-faceted experimental approach:

• Gene knockout or CRISPR-based genome editing:

  • Create an MS1271 deletion strain of M. succiniciproducens similar to the methodology used for other gene knockouts (MS0784, MS0807, etc.)

  • Analyze growth phenotypes under various conditions (different carbon sources, stress conditions)

  • Measure metabolite production, particularly succinic acid yield

• Localization studies:

  • Fluorescent protein fusions to determine subcellular localization

  • Immunogold electron microscopy using antibodies against MS1271

• Protein-protein interaction studies:

  • Bacterial two-hybrid analysis

  • Co-immunoprecipitation followed by mass spectrometry

  • Crosslinking studies

• Reconstitution into proteoliposomes:

  • Test transport function with various substrates

  • Measure ion conductance

• Structural analysis:

  • X-ray crystallography or cryo-electron microscopy

  • NMR studies of specific domains

How can site-directed mutagenesis be applied to study critical residues in MS1271?

Site-directed mutagenesis is a powerful approach for identifying functionally important residues within MS1271. The process should involve:

• Target selection:

  • Conserved residues identified through multiple sequence alignments

  • Charged residues within predicted transmembrane domains

  • Residues in predicted functional motifs

• Mutation design:

  • Conservative substitutions (maintaining similar physiochemical properties)

  • Non-conservative substitutions (changing charge, polarity, or size)

  • Alanine scanning of specific regions

• Expression system:

  • Use the established E. coli expression system with His-tagging

  • Consider complementation in a MS1271 knockout strain

• Functional assays:

  • Protein folding and stability assessment

  • Membrane integration efficiency

  • Functional complementation of phenotypes

  • Specific activity assays once a function is identified

A systematic mutagenesis approach might initially focus on regions with high conservation across UPF0299 family members, as these often indicate functionally critical domains.

What methods can be used to study the role of MS1271 in succinic acid production?

Studying MS1271's potential role in succinic acid production would require:

• Metabolic engineering approach:

  • Generate an MS1271 knockout strain in M. succiniciproducens

  • Compare succinic acid production between wild-type and mutant strains

  • Analyze the impact on fermentation parameters (yield, productivity, by-product formation)

• Growth medium optimization:

  • Test production using chemically defined medium (CDM) as described for M. succiniciproducens

  • Evaluate performance under different carbon sources (glucose, sucrose, etc.)

• Comparative metabolomics:

  • Measure intracellular metabolite concentrations in wild-type vs. MS1271 mutant

  • Identify metabolic bottlenecks or altered flux distributions

• Integration with existing metabolic engineering strategies:

  • Combine MS1271 manipulation with other known beneficial mutations

  • Compare with established succinic acid-producing strains like LPK7, which has multiple gene knockouts (ldhA, pflB, pta, ackA)

• Metabolic flux analysis:

  • Use 13C-labeled substrates to track carbon flow through metabolic pathways

  • Determine if MS1271 affects flux through the succinate-producing pathways

What are the challenges in crystallizing membrane proteins like MS1271?

Membrane proteins like MS1271 present significant challenges for structural determination, particularly crystallization. Researchers should be aware of:

• Solubilization challenges:

  • Selection of appropriate detergents for membrane extraction

  • Maintaining protein stability outside the native membrane environment

  • Ensuring homogeneity of the protein-detergent complex

• Crystallization difficulties:

  • Limited hydrophilic surface area for crystal contacts

  • Detergent micelles obscuring potential crystal contacts

  • Phase separation during crystallization trials

• Alternative approaches:

  • Lipidic cubic phase crystallization

  • Nanodiscs or amphipol stabilization

  • Fusion protein approaches (e.g., T4 lysozyme fusion)

  • Fab fragment co-crystallization

• Complementary structural methods:

  • Cryo-electron microscopy

  • Solid-state NMR

  • Small-angle X-ray scattering (SAXS)

A potential strategy for MS1271 would be to express truncated versions or stable domains if the full-length protein proves recalcitrant to crystallization.

How can MS1271 be used in comparative studies of bacterial membrane proteomes?

MS1271 offers opportunities for comparative membrane proteome studies:

• Proteomic analysis:

  • Compare membrane protein expression profiles between M. succiniciproducens and related organisms

  • Identify co-expressed proteins that might form functional complexes with MS1271

  • Study membrane proteome changes under different growth conditions

• Evolutionary analysis:

  • Compare MS1271 homologs across species

  • Investigate adaptive evolution of membrane proteins in different bacterial niches

• Structural biology:

  • Use MS1271 as a model for studying membrane protein folding and stability

  • Investigate lipid-protein interactions specific to rumen bacteria

• Biotechnological applications:

  • Explore potential for membrane protein engineering based on MS1271 structure

  • Investigate application in membrane protein expression systems