Recombinant Shewanella sp. Lipoprotein signal peptidase (lspA)
Description
Introduction to Lipoprotein Signal Peptidase (LspA)
Lipoprotein signal peptidase, also known as signal peptidase II (SPase II), is an essential membrane-bound enzyme in the lipoprotein biosynthetic pathway of Gram-negative bacteria. It plays a crucial role in the post-translational processing of bacterial lipoproteins by cleaving the signal peptide from prolipoproteins. This enzymatic activity is vital for bacterial viability, making LspA an attractive target for antibacterial drug discovery efforts, particularly against multidrug-resistant Gram-negative pathogens .
In the bacterial lipoprotein maturation pathway, LspA functions as the second enzyme in a sequential process. Initially, prolipoprotein diacylglyceryl transferase (Lgt) modifies the preprolipoprotein (ppBLP) to form the corresponding prolipoprotein (pBLP). Subsequently, LspA cleaves the signal peptide from the pBLP, producing a diacylated bacterial lipoprotein (DA-BLP). Finally, lipoprotein N-acyltransferase (Lnt) further modifies these lipoproteins for proper trafficking to the outer membrane in Gram-negative bacteria . The essential nature of this enzymatic cascade makes it an ideal target for antibiotic development.
Primary Structure and Domains
Recombinant Shewanella oneidensis LspA is a membrane protein consisting of 170 amino acids. The complete amino acid sequence is as follows:
MPLTWKDSGLRWYWVVVLVFLADQLSKQWVLANFDLFESVQLLPFFNFTYVRNYGAAFSFLSEAGGWQRWLFTIVAVGFSSLLTVWLRKQSASLLKLNLAYTLVIGGALGNLVDRLMHGFVVDFIDFYWGKSHYPAFNIADSAIFIGAVLIIWDSFFNSQSEQDKTEEVK
This protein sequence reveals a typical structure of a membrane-integrated peptidase with multiple transmembrane domains that are critical for its enzymatic function. The arrangement of hydrophobic and hydrophilic regions suggests that LspA is embedded in the bacterial inner membrane, where it can access newly synthesized prolipoproteins.
Comparison with LspA from Other Species
When compared to LspA from other bacterial species, such as Synechocystis sp., significant structural similarities can be observed despite some differences in sequence length. Synechocystis LspA consists of 161 amino acids compared to the 170 amino acids in Shewanella oneidensis LspA . Both proteins maintain the essential catalytic residues and structural features necessary for signal peptide cleavage, highlighting the evolutionary conservation of this enzyme across different bacterial species.
The amino acid sequence of Synechocystis sp. LspA is:
MARSFSLAKNPLFWQVAIAGIILDQLSKLWVSQAMDPVGTTWPLWSGVFHFTYVLNTGAAFSAFRGGAGWLKWLSLAVSVGLIIFAGKVPLRKLEQLGYGCILAGAVGNGIDRFLFGHVIDFLDFRLINFP
Comparative sequence analysis reveals conserved regions likely associated with catalytic activity and substrate recognition, while variations may reflect adaptations to different cellular environments and substrate specificities.
Role in Lipoprotein Biosynthesis
In Shewanella species, LspA performs the critical function of cleaving the signal peptide from prolipoproteins, an essential step in the maturation of bacterial lipoproteins. This process is vital for proper lipoprotein localization and function within the bacterial cell envelope. The cleavage occurs after a conserved sequence known as the lipobox, which contains the cysteine residue that becomes the N-terminal amino acid of the mature lipoprotein .
Mature lipoproteins in Shewanella serve numerous essential functions, including:
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Structural components of the cell envelope
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Transport of nutrients and other molecules
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Cell division and growth
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Adaptation to environmental stresses
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Respiration and electron transport processes
Given the versatility of Shewanella species in inhabiting various environments, from freshwater to deep-sea conditions, properly processed lipoproteins are crucial for their adaptability and survival .
Significance in Shewanella Biology
Shewanella species are known for their remarkable versatility in respiratory capabilities and their ability to synthesize various types of fatty acids, including monounsaturated fatty acids (MUFA) and branched-chain fatty acids (BCFA), with some species also producing eicosapentaenoic acid (EPA) . The proper processing of lipoproteins by LspA is integral to maintaining the structural integrity and function of membrane systems that support these metabolic capabilities.
The role of LspA becomes particularly significant given that Shewanella species inhabit diverse environmental niches, from freshwater sediments to deep-sea environments. The ability to properly process membrane lipoproteins likely contributes to the adaptability of these bacteria to various temperatures and pressures .
Expression Systems
Recombinant Shewanella oneidensis LspA has been successfully expressed in Escherichia coli expression systems. The typical approach involves fusing the LspA protein sequence with an N-terminal histidine tag (His-tag) to facilitate purification . The expression vector and E. coli strain selection are crucial for optimizing protein yield and maintaining proper folding of this membrane protein.
The expression of recombinant LspA presents several challenges due to its hydrophobic nature and multiple transmembrane domains. These challenges include:
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Potential toxicity to the host cell
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Protein misfolding and aggregation
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Reduced solubility and extraction efficiency
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Difficulties in maintaining native conformation during purification
Despite these challenges, optimized protocols have been developed to successfully express and purify functional recombinant LspA protein for research applications.
Purification Methods
The purification of recombinant His-tagged Shewanella LspA typically involves immobilized metal affinity chromatography (IMAC) using nickel or cobalt resins. Additional purification steps may include size exclusion chromatography or ion exchange chromatography to achieve higher purity levels. The purified protein is typically obtained at greater than 90% purity as determined by SDS-PAGE analysis .
After purification, the protein is commonly stored as a lyophilized powder, which enhances its stability during long-term storage. For experimental use, the protein can be reconstituted in an appropriate buffer, often supplemented with glycerol to prevent freeze-thaw damage .
| Property | Specification |
|---|---|
| Species | Shewanella oneidensis |
| Source | E. coli |
| Tag | His |
| Protein Length | Full Length (1-170) |
| Form | Lyophilized powder |
| Purity | >90% by SDS-PAGE |
| Storage Buffer | Tris/PBS-based buffer, 6% Trehalose, pH 8.0 |
| Storage Condition | -20°C/-80°C, avoid repeated freeze-thaw cycles |
| Reconstitution | Deionized sterile water to 0.1-1.0 mg/mL |
Enzymatic Assays and Inhibition Studies
Recombinant LspA serves as a valuable tool for enzymatic assays designed to evaluate its activity and potential inhibitors. A common approach involves using a SDS-PAGE gel-shift assay, where the cleavage of a model substrate (such as prepro inhibitor of cysteine protease, ppICP) can be monitored by tracking the change in molecular weight after signal peptide removal . This assay provides a reliable method to quantify LspA activity and to screen for potential inhibitors.
Such enzymatic assays have been instrumental in identifying and characterizing compounds that inhibit LspA activity, including natural products like globomycin and synthetic peptide analogues. These inhibition studies are crucial for understanding the structure-activity relationships and for developing more potent and selective inhibitors with potential therapeutic applications.
Therapeutic Potential
The essential nature of LspA for bacterial viability, coupled with its absence in human cells, makes it an attractive target for antibacterial drug development. Inhibition of LspA by compounds such as globomycin and myxovirescin has been shown to induce bacterial cell death, confirming its potential as a therapeutic target . This is particularly significant in the context of the growing threat of multidrug-resistant Gram-negative bacteria.
Recent computational design approaches have led to the development of stable cyclic peptide analogues of globomycin that show potent inhibition of LspA. These designed inhibitors have demonstrated antimicrobial activity against ESKAPE-E pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter species, and Escherichia coli), highlighting the therapeutic potential of targeting LspA .
Advantages Over Traditional Antibiotic Targets
Targeting LspA as an antibacterial strategy offers several advantages over traditional antibiotic targets:
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Novel mechanism of action, reducing the risk of cross-resistance with existing antibiotics
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Essential function in bacteria without a human homolog, minimizing potential toxicity
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Conserved across various bacterial species, offering broad-spectrum potential
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Membrane-associated target, potentially circumventing efflux-mediated resistance mechanisms
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Validated by natural product inhibitors, demonstrating the feasibility of inhibition
These advantages position LspA inhibitors as promising candidates for addressing the growing challenge of antibiotic resistance, particularly in Gram-negative pathogens.
Functional Conservation Across Species
Despite sequence variations, the fundamental function of LspA appears to be highly conserved across different bacterial species. This functional conservation underscores the essential nature of lipoprotein processing in bacterial physiology and validates LspA as a broad-spectrum antibacterial target.
Recent Advances in LspA Research
Recent research on bacterial LspA has focused on several key areas:
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Computational design of stable cyclic peptide inhibitors as alternatives to natural products like globomycin
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Development of high-throughput screening assays for identifying novel LspA inhibitors
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Structural studies to elucidate the catalytic mechanism and inhibitor binding modes
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Investigation of species-specific variations in LspA structure and function
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Evaluation of LspA inhibitors against clinically relevant bacterial pathogens
These research efforts have significantly advanced our understanding of LspA biology and have generated promising leads for antibacterial drug development.
Future Research Directions
Several promising research directions could further enhance our understanding of Shewanella LspA and accelerate the development of LspA-targeting antibiotics:
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Comprehensive structural characterization of Shewanella LspA through crystallography or cryo-EM
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Detailed analysis of the substrate specificity determinants specific to Shewanella LspA
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Development of selective inhibitors targeting Shewanella LspA for research applications
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Investigation of the role of LspA in Shewanella adaptation to extreme environments
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Exploration of LspA as a potential biomarker for Shewanella species identification
Additionally, the further optimization of expression and purification protocols for recombinant Shewanella LspA would facilitate these research endeavors by providing increased yields of high-quality protein for structural and functional studies.
Product Specs
Note: We will prioritize shipping the format we have in stock. However, if you have a specific format preference, please indicate your requirement when placing the order. We will prepare the product according to your demand.
Note: All our proteins are shipped with standard blue ice packs. If you require dry ice shipping, please communicate with us in advance, as additional fees may apply.
Generally, the shelf life of liquid form is 6 months at -20°C/-80°C. The shelf life of lyophilized form is 12 months at -20°C/-80°C.
Target Background
KEGG: shm:Shewmr7_3038
Q&A
What is LspA and what role does it play in bacterial physiology?
LspA (lipoprotein signal peptidase) is a type II signal peptidase (SPase II) that functions as an essential component of lipoprotein processing in gram-negative bacteria. It is a membrane-bound aspartyl protease that cleaves the transmembrane helix signal peptide of lipoproteins as part of the lipoprotein-processing pathway. LspA has been identified in both gram-negative and gram-positive bacteria but is not found in archaea or eukaryotes . In gram-negative bacteria like Shewanella sp., LspA is essential for viability, while in many gram-positive bacteria, it has been shown to be dispensable for growth but important for virulence .
What are the conserved structural domains of LspA that are critical for its function?
LspA contains highly conserved domains essential for its proteolytic activity. The catalytic core of LspA includes conserved aspartic acid, asparagine, and alanine residues that are critical for its function as an aspartyl protease . Sequence alignment studies across bacterial species reveal specific conserved boxes (such as boxes C and D identified in Rickettsia typhi) that contain these essential catalytic residues . Additionally, LspA possesses a highly conserved periplasmic helix (PH) that plays a crucial role in substrate binding and recognition, exhibiting conformational flexibility that enables it to accommodate various lipoprotein substrates .
What are the optimal expression systems for producing recombinant Shewanella sp. LspA?
Based on successful recombinant expression of LspA from other bacterial species, E. coli systems provide a viable platform for recombinant Shewanella sp. LspA production. When expressing Rickettsia typhi LspA in E. coli, researchers used plasmid vectors like pMW119 with successful results . For optimal expression of membrane-bound proteins like LspA, consider specialized E. coli strains designed for membrane protein expression (such as C41(DE3) or C43(DE3)). Expression conditions should be optimized by testing different induction temperatures (typically 18-30°C), inducer concentrations, and expression durations. Low-temperature induction often improves the folding and membrane integration of recombinant membrane proteins. Depending on experimental goals, consider adding a purification tag (His6, FLAG, etc.) that doesn't interfere with the catalytic activity of the enzyme.
How can the functional activity of recombinant Shewanella sp. LspA be assessed?
Two established methods for assessing the functional activity of recombinant LspA include the globomycin resistance assay and genetic complementation. In the globomycin resistance assay, E. coli cells expressing functional LspA demonstrate increased resistance to the antibiotic globomycin . Researchers can measure bacterial growth in the presence of increasing concentrations of globomycin (ranging from 12.5 to 200 μg/ml) and compare growth rates between cells expressing recombinant LspA and control cells . For genetic complementation, a temperature-sensitive E. coli strain with defective LspA (such as E. coli Y815) can be transformed with recombinant Shewanella sp. LspA, and growth restoration at non-permissive temperatures (42°C) would indicate functional activity . Both methods provide quantitative measures of LspA activity and are complementary approaches for functional characterization.
What approaches can be used to study the conformational dynamics of Shewanella sp. LspA?
Conformational dynamics of LspA can be studied using a combination of molecular dynamics (MD) simulations and electron paramagnetic resonance (EPR) spectroscopy . For MD simulations, researchers should first determine the three-dimensional structure of Shewanella sp. LspA through X-ray crystallography, cryo-EM, or homology modeling based on available LspA structures from other bacteria. MD simulations can then be performed in a lipid bilayer environment to analyze nanosecond-scale conformational changes, particularly focusing on the movement of the periplasmic helix. For EPR studies, strategic residues in the periplasmic helix and active site can be labeled with spin probes to monitor conformational shifts between open and closed states . These methodologies would reveal how Shewanella sp. LspA transitions between different conformational states important for substrate binding and catalysis.
How does substrate specificity differ between Shewanella sp. LspA and other bacterial LspAs?
Investigating substrate specificity differences requires systematic analysis of lipoprotein processing by different LspA homologs. Begin by performing in silico analysis using prediction tools like SignalP and LipoP to identify potential lipoprotein substrates in the Shewanella sp. genome . Next, develop a comparative processing assay using a panel of purified prolipoproteins from different bacterial sources to test cleavage efficiency by recombinant Shewanella sp. LspA versus other bacterial LspAs. Mass spectrometry analysis of cleavage products can precisely identify the cleavage sites. Additionally, create chimeric LspA proteins with domains swapped between Shewanella sp. and other bacterial LspAs to identify regions responsible for substrate recognition and specificity. Complementation studies in LspA-deficient strains from different bacterial backgrounds can further reveal the degree of functional conservation and substrate overlap.
What is the relationship between LspA expression kinetics and bacterial infection cycles?
To investigate the relationship between LspA expression and infection cycles in Shewanella sp., researchers should implement a time-course analysis similar to that performed for Rickettsia typhi . This requires establishing an appropriate infection model where Shewanella sp. interactions with host cells can be monitored. Real-time quantitative reverse transcription-PCR (qRT-PCR) should be used to track the expression levels of lspA and related genes (like lgt encoding prolipoprotein transferase and lepB encoding type I signal peptidase) at various timepoints throughout the infection cycle . Comparison of expression patterns between these genes can reveal coordinated regulation of protein secretion pathways. Additionally, constructing fluorescent reporter strains where lspA promoter activity drives fluorescent protein expression would allow real-time visualization of expression dynamics during infection. Correlation of expression data with bacterial replication rates, host cell responses, and virulence factor production will provide insight into the functional importance of LspA during different infection stages.
How do mutations in catalytic domains affect the structure-function relationship of Shewanella sp. LspA?
Investigating structure-function relationships requires a systematic site-directed mutagenesis approach targeting the conserved catalytic residues and domains identified through sequence alignment. Based on LspA studies in other bacteria, focus on the conserved aspartic acid, asparagine, and alanine residues in the catalytic site, particularly those in the conserved boxes C and D . For each mutant, assess: (1) protein expression and membrane localization using Western blotting and subcellular fractionation; (2) conformational integrity using circular dichroism spectroscopy or limited proteolysis; (3) substrate binding capacity using fluorescently labeled substrate analogs; and (4) catalytic activity using the globomycin resistance and genetic complementation assays . Additionally, perform MD simulations on wildtype and mutant forms to predict how specific mutations affect the conformational dynamics, particularly the movement of the periplasmic helix known to be crucial for substrate binding . This comprehensive approach will establish clear connections between specific residues and their roles in the catalytic mechanism of Shewanella sp. LspA.
How should discrepancies between in vitro and in vivo activity of recombinant Shewanella sp. LspA be interpreted?
Discrepancies between in vitro and in vivo activity of recombinant LspA are commonly observed and require careful interpretation. When R. typhi LspA was expressed in E. coli, it showed significant functional activity but at lower levels than native E. coli LspA in complementation assays . These differences may arise from several factors: (1) membrane composition differences between Shewanella sp. and heterologous expression systems affecting proper membrane insertion and folding; (2) differential post-translational modifications; (3) absence of Shewanella-specific interaction partners; or (4) suboptimal expression levels. To address these discrepancies, researchers should: compare membrane lipid compositions between native and heterologous systems; examine expression levels using quantitative Western blotting; test activity in membrane preparations versus intact cells; and evaluate potential cofactor requirements. Additionally, consider constructing chimeric proteins that combine domains from Shewanella sp. LspA with E. coli LspA to identify regions responsible for the functional discrepancies observed between in vitro and in vivo systems.
What statistical approaches are most appropriate for analyzing LspA conformational dynamics data?
For conformational dynamics data from MD simulations and EPR spectroscopy, several specialized statistical approaches are recommended. For MD trajectory analysis, perform principal component analysis (PCA) to identify the major modes of protein motion, particularly focusing on the periplasmic helix fluctuations identified as critical in LspA function . Calculate root-mean-square deviation (RMSD) and root-mean-square fluctuation (RMSF) values to quantify structural variations over time. For identifying distinct conformational states, employ clustering algorithms (such as k-means or DBSCAN) based on structural similarity metrics. When analyzing EPR data, use spectral deconvolution techniques to distinguish between different conformational populations, and apply Boltzmann statistics to estimate the relative energies of different conformational states . For both MD and EPR data, Markov state modeling can help identify the transitions between different conformational states and calculate the associated energy barriers. Statistical significance of differences between apo and substrate/inhibitor-bound states should be assessed using appropriate statistical tests (t-tests, ANOVA, or non-parametric alternatives) depending on data distribution.
What are the most promising approaches for developing LspA inhibitors targeting Shewanella sp.?
Development of LspA inhibitors targeting Shewanella sp. should build upon successful approaches with known LspA inhibitors like globomycin and myxovirescin . Structure-based drug design informed by conformational dynamics is particularly promising—the flexible periplasmic helix and its role in substrate binding provide opportunities for inhibitor development . Researchers should focus on compounds that stabilize the closed conformation of LspA, thereby preventing substrate access to the active site. High-throughput screening of compound libraries against recombinant Shewanella sp. LspA, followed by structural and biochemical characterization of hits, provides a direct path to inhibitor discovery. Additionally, in silico screening using molecular docking against different conformational states of LspA can identify novel chemical scaffolds for optimization. The high conservation of active site residues across bacterial species suggests that broad-spectrum inhibitors may be possible, while targeting less conserved regions might yield Shewanella-specific inhibitors . Evaluate candidate inhibitors not only for their direct LspA inhibition but also for their effects on bacterial viability, virulence, and resistance development potential.
How can transcriptomic and proteomic approaches enhance our understanding of LspA's role in Shewanella sp.?
Integrative -omics approaches offer powerful insights into LspA's physiological role. RNA-seq analysis comparing wildtype and LspA-depleted Shewanella sp. strains can reveal transcriptional networks affected by LspA disruption, identifying genes co-regulated with lspA and potential compensatory mechanisms. Quantitative proteomics using techniques like SILAC (Stable Isotope Labeling with Amino acids in Cell culture) or TMT (Tandem Mass Tag) labeling can identify which lipoproteins are most affected by LspA depletion or inhibition, helping prioritize the most critical LspA substrates . Secretome analysis comparing wildtype and LspA-depleted strains can directly identify lipoproteins dependent on LspA processing. ChIP-seq (Chromatin Immunoprecipitation sequencing) targeting transcription factors differentially expressed upon LspA disruption can map the regulatory networks controlling lipoprotein processing machinery. Correlation of these datasets with phenotypic changes in growth, stress response, and virulence provides a systems-level understanding of LspA's importance. Researchers should implement these approaches across different growth conditions and environmental stresses to develop a comprehensive model of when and how LspA activity becomes critical for Shewanella sp. survival and pathogenicity.
