Recombinant Shigella boydii serotype 18 UPF0283 membrane protein ycjF (ycjF)

What is UPF0283 membrane protein YcjF from Shigella boydii?

UPF0283 membrane protein YcjF is a full-length 353 amino acid protein found in Shigella boydii bacteria. It belongs to the UPF0283 protein family, a group of uncharacterized membrane proteins that are widely conserved across bacterial species. The protein contains multiple transmembrane domains and is likely integrated into the bacterial cell membrane. According to sequence data, the protein from Shigella boydii serotype 4 contains a mix of hydrophilic and hydrophobic regions consistent with its membrane localization, with an amino acid sequence beginning with MTEPLKPRID and continuing through to KETLQKGKTPSEK at the C-terminus .

The UPF prefix (Uncharacterized Protein Family) indicates that while the protein has been identified and sequenced, its specific biological function remains to be fully elucidated. In Shigella boydii, YcjF has been assigned the UniProt ID Q320A9, which serves as the reference identifier for this protein in various databases .

What expression systems are effective for recombinant production of YcjF?

For recombinant production of Shigella boydii YcjF, Escherichia coli serves as the most effective and widely used expression system. This approach leverages the close genetic relationship between E. coli and Shigella, which share significant genomic similarity. The commercially available recombinant YcjF protein is typically expressed in E. coli with an N-terminal His tag to facilitate purification .

For optimal expression, researchers should consider the following methodological approach:

• Vector selection: pET-based expression vectors with T7 promoters generally provide high-yield expression for bacterial membrane proteins

• E. coli strain optimization: BL21(DE3) or C41/C43(DE3) strains are often preferable for membrane protein expression

• Induction conditions: Lower temperatures (16-20°C) and reduced IPTG concentrations (0.1-0.5 mM) typically improve proper folding

• Growth media: Enriched media such as Terrific Broth can enhance yield

The effectiveness of the expression system can be assessed through SDS-PAGE analysis, with expected purity greater than 90% for properly optimized systems .

How does the amino acid composition of YcjF contribute to its membrane localization pattern?

The amino acid sequence of YcjF reveals distinctive hydrophobic regions that are characteristic of transmembrane domains. Analysis of the 353-amino acid sequence shows alternating hydrophobic and hydrophilic segments that create a topology consistent with multiple membrane-spanning regions .

The primary sequence contains several notable features contributing to membrane localization:

• Hydrophobic core segments: Multiple stretches of hydrophobic residues (e.g., "MVMGGLALFGASVVGQGVQWTMNAWQTQDWVALGGCAAGALIIGAGVGSVV") form the transmembrane helices

• Charged residue distribution: Positively charged residues (Arg, Lys) appear more frequently on cytoplasmic-facing segments, following the "positive-inside rule" of membrane protein topology

• Aromatic residue positioning: Tryptophan and tyrosine residues are strategically positioned at membrane-water interfaces to anchor the protein

• Loop regions: Hydrophilic stretches connecting transmembrane domains form loop regions of varying lengths

This compositional pattern creates a multi-pass membrane protein with an estimated 6-8 transmembrane helices based on hydropathy analysis of the sequence. The AlphaFold computational model confirms this general architecture, providing additional structural insights into the membrane integration pattern .

What computational models exist for YcjF and how reliable are they?

Two primary computational models exist for YcjF proteins from Shigella boydii and the closely related Escherichia coli. Both models were generated through AlphaFold and are available in the AlphaFold Database:

• Shigella boydii Sb227 YcjF (UniProt ID: Q320A9): Model identifier AF-Q320A9-F1, with a global pLDDT (predicted Local Distance Difference Test) score of 72.84

• Escherichia coli APEC O1 YcjF (UniProt ID: A1AAT4): Model identifier AF-A1AAT4-F1, with a global pLDDT score of 74.1

The reliability of these models can be assessed through their pLDDT confidence metrics:

The reliability varies across different regions of the protein, with transmembrane helices typically showing higher confidence scores than loop regions or terminal segments. For research requiring atomic-level precision, these models should be considered starting points rather than definitive structures.

What methods would be most appropriate for experimental validation of the YcjF structure?

Experimental validation of the YcjF computational structure requires complementary approaches that address different aspects of membrane protein structure:

• Cryo-electron microscopy (Cryo-EM)

  • Advantages: Does not require crystallization; can capture native membrane environment

  • Methodology: Purify YcjF in detergent micelles or nanodiscs; prepare vitrified samples; collect and process image data

  • Expected resolution: 3-4Å resolution is achievable for membrane proteins of this size (~40 kDa)

• X-ray crystallography

  • Challenges: Membrane protein crystallization is notoriously difficult

  • Methodology: Screen hundreds of crystallization conditions with varying detergents; consider lipidic cubic phase crystallization

  • Enhancement strategies: Use thermostabilizing mutations or antibody fragments to improve crystallization properties

• Nuclear Magnetic Resonance (NMR) spectroscopy for domain validation

  • Application: Better suited for individual domains rather than full-length protein

  • Methodology: Express isotopically labeled domains (13C, 15N); collect multi-dimensional NMR spectra

  • Analysis: Compare experimental chemical shifts with those predicted from the computational model

• Cross-linking Mass Spectrometry (XL-MS)

  • Principle: Chemical cross-links between spatially proximal residues provide distance constraints

  • Methodology: React purified YcjF with cross-linking reagents; digest; identify cross-linked peptides by MS/MS

  • Analysis: Compare experimental cross-links with distances predicted by the computational model

• Hydrogen-Deuterium Exchange Mass Spectrometry (HDX-MS)

  • Application: Identifies solvent-exposed regions and secondary structure elements

  • Methodology: Expose purified YcjF to D2O buffer; quench at various timepoints; analyze deuterium incorporation

  • Validation: Compare experimental solvent accessibility with model predictions

A comprehensive validation strategy would integrate data from multiple methods, beginning with lower-resolution techniques like HDX-MS and XL-MS before pursuing high-resolution structural studies by cryo-EM or X-ray crystallography.

What purification strategies address the challenges specific to YcjF as a membrane protein?

Purifying membrane proteins like YcjF presents unique challenges that require specialized approaches. Based on the available information about recombinant YcjF production, the following multi-step strategy is recommended:

• Membrane isolation and solubilization

  • Lyse cells expressing His-tagged YcjF using mechanical disruption (e.g., sonication, high-pressure homogenization)

  • Separate membranes by ultracentrifugation (100,000 × g for 1 hour)

  • Solubilize membranes with appropriate detergents:

    • Primary screen: DDM (n-Dodecyl β-D-maltoside), LMNG (Lauryl maltose neopentyl glycol), or UDM (n-Undecyl-β-D-maltopyranoside)

    • Secondary screen: Digitonin, DMNG, or Triton X-100 at 1-2% concentrations

• Affinity chromatography

  • Apply solubilized material to Ni-NTA resin (leveraging the N-terminal His tag)

  • Wash extensively with buffer containing reduced detergent (0.1-0.2%)

  • Include stepped imidazole washes (20-50 mM) to reduce non-specific binding

  • Elute YcjF with high imidazole (250-300 mM)

• Size exclusion chromatography (SEC)

  • Further purify YcjF by SEC using Superdex 200 or similar matrix

  • Monitor protein quality by assessing monodispersity of the SEC peak

  • Expected purity: >90% as determined by SDS-PAGE

• Detergent exchange (if needed)

  • For functional studies, consider exchanging harsh solubilization detergents for milder options

  • Alternatives to traditional detergents: Amphipols, nanodiscs, or SMALPs for increased stability

• Quality control assessments

  • Thermal stability assays (e.g., Differential Scanning Fluorimetry)

  • Dynamic Light Scattering to confirm monodispersity

  • Circular Dichroism to verify secondary structure integrity

This purification strategy should yield YcjF protein suitable for both functional and structural studies, addressing the specific challenges of membrane protein purification.

What are the optimal storage conditions for maintaining YcjF stability?

Maintaining the stability of membrane proteins like YcjF during storage is crucial for preserving their structural integrity and functional properties. Based on the information provided for the recombinant YcjF protein, the following storage recommendations should be implemented:

• Short-term storage (up to one week)

  • Store working aliquots at 4°C

  • Maintain in Tris/PBS-based buffer with 6% trehalose at pH 8.0

  • Avoid repeated freeze-thaw cycles as this is specifically not recommended for this protein

• Long-term storage

  • Store at -20°C/-80°C in small aliquots

  • Add glycerol to a final concentration of 20-50% (with 50% being the recommended default)

  • Ensure samples are flash-frozen in liquid nitrogen before transferring to freezer storage

• Lyophilization considerations

  • The commercial YcjF product is supplied as a lyophilized powder

  • For reconstitution, use deionized sterile water to achieve a concentration of 0.1-1.0 mg/mL

  • After reconstitution, add glycerol before aliquoting for long-term storage

• Buffer components for optimal stability

  • Base buffer: Tris/PBS at pH 8.0

  • Stabilizing agents: 6% trehalose serves as a protein stabilizer

  • Detergent: Maintain at concentrations above CMC but below levels that might destabilize the protein

• Stability monitoring

  • Perform periodic SDS-PAGE analysis to check for degradation

  • For critical applications, verify structural integrity via circular dichroism before use

  • Monitor aggregation using techniques like dynamic light scattering

The inclusion of 6% trehalose in the storage buffer is particularly noteworthy, as trehalose is an exceptional stabilizing agent for membrane proteins due to its ability to preserve protein structure during freeze-thaw cycles and prevent aggregation. The specific recommendation against repeated freeze-thaw cycles indicates that YcjF may be particularly sensitive to this form of stress .

What is the known or predicted function of YcjF in Shigella boydii?

• Membrane transport

  • The multi-pass transmembrane architecture suggests a potential role in small molecule transport

  • Structural features resemble secondary active transporters, possibly involved in ion or nutrient transport

  • May function in maintaining membrane potential or facilitating nutrient acquisition

• Signaling or sensory functions

  • The protein's membrane localization positions it to potentially sense environmental changes

  • Could function as part of a two-component regulatory system responding to extracellular signals

  • May participate in quorum sensing or host environment detection during infection

• Membrane integrity

  • May contribute to membrane stability under stress conditions

  • Could participate in lipid organization or membrane microdomain formation

  • Potential role in maintaining membrane protein complexes

• Pathogenesis-related functions

  • As a conserved protein in a pathogenic bacterium, YcjF may contribute to virulence

  • Could be involved in host-pathogen interactions or intracellular survival mechanisms

  • May participate in stress response pathways activated during infection

Based on its high conservation across bacterial species, YcjF likely performs a fundamental cellular function rather than a specialized role unique to Shigella. The confident prediction of its membrane localization is supported by both sequence analysis and computational modeling , but experimental functional characterization remains the critical next step in understanding this protein's biological role.

What experimental approaches would be most effective for elucidating YcjF function?

Elucidating the function of uncharacterized proteins like YcjF requires a multi-faceted approach combining genetic, biochemical, and computational methods:

• Genetic manipulation strategies

  • CRISPR-Cas9 or transposon-based knockout: Generate ycjF deletion mutants in Shigella boydii

  • Complementation analysis: Reintroduce wild-type and mutant versions to confirm phenotypes

  • Conditional expression systems: Create depletion strains to observe effects of reduced YcjF levels

  • Methodology: Compare growth rates, stress responses, and virulence properties between wild-type and mutant strains

• Protein interaction studies

  • Bacterial two-hybrid screening: Identify protein interaction partners

  • Co-immunoprecipitation with anti-His antibodies: Pull down protein complexes containing His-tagged YcjF

  • Crosslinking mass spectrometry: Capture transient interactions

  • Analytical pipeline: Validate interactions through reciprocal pull-downs and functional co-dependency tests

• Localization and trafficking analysis

  • Fluorescent protein fusions: Visualize subcellular localization under different conditions

  • Immunogold electron microscopy: Achieve high-resolution localization within the bacterial membrane

  • Fractionation studies: Determine specific membrane domains where YcjF resides

  • Analysis approach: Quantify distribution patterns and co-localization with known membrane proteins

• Functional biochemical assays

  • Transport assays: Measure movement of various substrates in proteoliposomes containing purified YcjF

  • Electrophysiology: Assess potential channel or transporter activity using patch-clamp techniques

  • Binding assays: Identify potential ligands or substrates that interact with YcjF

  • Data integration: Correlate biochemical activities with phenotypic observations from genetic studies

• Comparative genomics and evolutionary analysis

  • Synteny analysis: Examine genomic context of ycjF across bacterial species

  • Co-evolution studies: Identify proteins that show coordinated evolutionary patterns with YcjF

  • Methodology: Apply computational algorithms to detect functional associations based on genomic proximity and co-occurrence patterns

An integrated approach combining these methods would provide the most comprehensive understanding of YcjF function, with initial computational analyses guiding targeted experimental hypotheses.

How does YcjF from Shigella boydii compare structurally to homologs in Escherichia coli?

The structural comparison between Shigella boydii YcjF and its Escherichia coli homolog reveals striking similarities with subtle differences that may relate to species-specific functions:

The high structural similarity between S. boydii and E. coli YcjF proteins is consistent with the close phylogenetic relationship between these bacterial genera. Shigella is sometimes considered to be within the E. coli species complex from a genomic perspective, which explains the remarkable conservation of protein structures. This structural conservation suggests that findings regarding E. coli YcjF function may be largely applicable to the S. boydii homolog, providing a broader experimental basis for understanding this protein family .

What can phylogenetic analysis reveal about YcjF conservation and potential function?

Phylogenetic analysis of YcjF proteins across bacterial species provides valuable insights into its evolutionary history and potential functional significance:

• Taxonomic distribution pattern

  • YcjF homologs are widely distributed throughout the Enterobacteriaceae family

  • The protein is highly conserved in multiple genera including Shigella, Escherichia, Salmonella, and Klebsiella

  • Conservation extends beyond Enterobacteriaceae to other Gammaproteobacteria, suggesting an ancient origin

  • This broad distribution indicates YcjF likely performs a fundamental cellular function rather than a niche-specific role

• Sequence conservation analysis

  • Core transmembrane domains show higher sequence conservation than loop regions

  • Specific residues within presumed active sites or binding pockets display near-complete conservation

  • The N-terminal cytoplasmic domain exhibits greater sequence variation than the membrane-embedded regions

  • This pattern suggests functional constraints on the membrane domains while allowing species-specific adaptations in cytoplasmic regions

• Co-evolutionary relationships

  • Genes frequently co-occurring with ycjF in bacterial genomes include:

    • Components of membrane biogenesis pathways

    • Stress response regulators

    • Specific transporters and permeases

  • This genomic association pattern supports potential roles in membrane homeostasis or stress response

• Evolutionary rate analysis

• Pathogen-specific adaptations

  • Subtle sequence variations between pathogenic (Shigella) and commensal (some E. coli) strains

  • These differences may reflect adaptations to pathogenic lifestyle requirements

  • Key variations cluster in regions potentially involved in host interaction or stress response

The high conservation of YcjF across diverse bacterial species, coupled with evidence of strong selective pressure on transmembrane regions, strongly suggests it performs an essential cellular function. The phylogenetic pattern is consistent with roles in fundamental processes such as membrane homeostasis, environmental sensing, or stress response rather than specialized virulence functions, despite its presence in pathogenic species like Shigella boydii .

What are the most significant knowledge gaps in YcjF research?

Despite the computational structural models and sequence information available for YcjF, several critical knowledge gaps remain that present opportunities for groundbreaking research:

• Functional characterization

  • The biological function of YcjF remains entirely unknown, as indicated by its UPF (Uncharacterized Protein Family) designation

  • No experimental evidence exists regarding potential substrates, binding partners, or biochemical activities

  • The relationship between structure and function has not been established through mutagenesis or functional assays

  • This fundamental gap represents both the greatest challenge and opportunity in YcjF research

• Experimental structural validation

  • Current structural information relies solely on computational predictions (AlphaFold models)

  • No experimental structures (X-ray crystallography, cryo-EM, or NMR) exist to validate these models

  • The precise membrane topology and orientation remain to be experimentally confirmed

  • Resolution of this gap would provide critical insights for functional hypotheses and rational experimental design

• Regulation and expression patterns

  • The conditions that regulate ycjF expression in Shigella boydii are unknown

  • Whether expression changes during infection, stress response, or different growth phases is unexplored

  • Transcriptional and post-translational regulatory mechanisms remain to be characterized

  • Understanding when and how this protein is expressed would provide vital contextual clues to its function

• Role in bacterial physiology and pathogenesis

  • The contribution of YcjF to Shigella boydii survival, growth, and virulence is undefined

  • Whether YcjF functions differently in pathogenic versus non-pathogenic bacteria is unknown

  • The potential involvement in stress response, antibiotic resistance, or host interaction remains speculative

  • This gap limits our understanding of both basic bacterial physiology and potential therapeutic targeting

• Interactome and protein complex formation

  • No known interaction partners for YcjF have been experimentally identified

  • Whether YcjF functions independently or as part of larger protein complexes is unknown

  • Potential integration into known membrane protein networks or pathways remains to be established

  • Resolving this gap would position YcjF within the broader context of cellular function

These knowledge gaps collectively represent a significant opportunity for researchers to make fundamental contributions to understanding bacterial membrane protein biology, potentially revealing new aspects of Shigella physiology and pathogenesis with implications for antibacterial development.

What methodological advancements would most benefit future YcjF research?

Advancing our understanding of YcjF will require innovative methodological approaches that address the unique challenges of membrane protein research:

• Improved membrane protein expression systems

  • Development of specialized expression vectors optimized for bacterial membrane proteins

  • Engineering of host strains with enhanced membrane protein folding machinery

  • Implementation of controlled membrane protein induction systems to prevent toxicity

  • These advancements would improve yield and quality of recombinant YcjF for functional studies

• Membrane protein structural biology innovations

  • Application of emerging techniques like microcrystal electron diffraction (MicroED)

  • Development of novel membrane mimetics that better preserve native protein environments

  • Integration of computational approaches with sparse experimental data for hybrid modeling

  • Such technologies would facilitate experimental validation of the computational YcjF models

• High-throughput functional screening

  • Development of phenotypic microarrays specifically designed for membrane protein function discovery

  • Implementation of targeted CRISPR-Cas9 screens to identify genetic interactions

  • Creation of substrate libraries for systematic transport or binding assays

  • These approaches would accelerate functional annotation of YcjF and related proteins

• Advanced imaging technologies

  • Super-resolution microscopy techniques optimized for bacterial membrane proteins

  • Correlative light and electron microscopy approaches for dynamic localization studies

  • Single-molecule tracking methods to monitor YcjF behavior in living cells

  • These visualization tools would provide insights into subcellular dynamics and interactions

• Integrative multi-omics approaches

• Computational method advancements

  • Improved algorithms for membrane protein function prediction from sequence and structure

  • Enhanced molecular dynamics simulations specific to bacterial membrane environments

  • Machine learning approaches integrating diverse data types for functional inference

  • These computational tools would guide experimental design and interpret complex datasets