Recombinant Methanopyrus kandleri Protein translocase subunit SecD (secD)
Description
Definition and Biological Context
The SecD subunit forms part of the SecDF complex, which interacts with the core SecYEG translocon to enhance protein translocation efficiency. In M. kandleri, SecD is encoded by the secD gene (locus MK1009) and functions alongside SecF to stabilize the translocon and utilize proton motive force for post-translational protein export . Recombinant versions are produced in E. coli or baculovirus systems for research applications .
Functional Roles
-
Translocation Enhancement: Works with SecF to improve the rate of protein export via the SecYEG channel .
-
Proton Motive Force Utilization: Couples translocation with ion gradients to drive substrate release .
-
Membrane Protein Biogenesis: Assists in the insertion of polytopic membrane proteins .
Research Applications
Recombinant SecD is critical for in vitro studies of archaeal protein translocation mechanisms. Key applications include:
-
Biochemical Assays: Reconstitution of translocon complexes to study kinetics .
-
Structural Studies: Purification for cryo-EM or X-ray crystallography trials (though no published structures yet) .
-
Thermostability Investigations: M. kandleri SecD’s stability at high temperatures (>80°C) provides insights into extremophile adaptations .
Production and Handling
Data from commercial recombinant SecD products reveal standardized protocols:
Comparative Genomics
-
Archaeal vs. Bacterial SecD: Unlike bacteria, M. kandleri SecD operates without SecA ATPase, relying solely on proton gradients .
-
Conservation: SecD homologs are present in all sequenced methanogens, underscoring their essential role .
Challenges and Future Directions
Product Specs
Note: We prioritize shipping the format currently in stock. However, if you have a specific format requirement, please indicate it during order placement, and we will accommodate your request.
Note: All proteins are shipped with standard blue ice packs. If you require dry ice shipping, please inform us in advance as additional fees will apply.
Generally, liquid forms have a shelf life of 6 months at -20°C/-80°C. Lyophilized forms have a shelf life of 12 months at -20°C/-80°C.
Target Background
KEGG: mka:MK1009
STRING: 190192.MK1009
Q&A
FAQs for Researchers: Recombinant Methanopyrus kandleri Protein Translocase Subunit SecD (SecD)
What is the functional role of SecD in Methanopyrus kandleri protein translocation?
SecD, part of the SecDF-YajC complex in prokaryotes, facilitates post-translational protein translocation by stabilizing the SecYEG translocon and coupling proton motive force to substrate release . In M. kandleri, SecD enhances the efficiency of secretory protein transport across the cytoplasmic membrane, particularly under extreme thermophilic conditions (80–110°C). Experimental validation involves:
-
Knockout studies: Compare translocation rates in secD-deficient vs. wild-type strains using radiolabeled substrates.
-
Proteomic profiling: Identify accumulated pre-proteins in cytoplasmic fractions via mass spectrometry .
Table 1: Key Functional Domains in M. kandleri SecD
How is recombinant M. kandleri SecD expressed and purified for structural studies?
Recombinant SecD (UniProt: Q8TWM4) is typically expressed in E. coli with a His-tag and purified via:
-
Thermostable extraction: Lyse cells in Tris buffer (pH 8.0) at 70°C to denature host proteins, retaining SecD solubility .
-
Immobilized metal affinity chromatography (IMAC): Use Ni-NTA resins with imidazole elution (50–250 mM gradient).
-
Size-exclusion chromatography: Resolve oligomeric states in Tris-based buffer with 50% glycerol .
Challenges:
-
Aggregation: Mitigated by adding 6% trehalose to storage buffers .
-
Proteolysis: Avoid repeated freeze-thaw cycles; store aliquots at -80°C .
What bioinformatics tools are critical for predicting SecD interactions in M. kandleri?
-
AlphaFold2: Predicts 3D structure of SecD (residues 1–403) with RMSD <2.0 Å against experimental models .
-
STRING-DB: Identifies functional partners (e.g., SecE, SecF) via co-conservation analysis .
-
MEMSAT-SVM: Maps transmembrane helices (TMS1–TMS12) with 94% accuracy .
How do structural dynamics of SecD differ between M. kandleri and mesophilic homologs?
Methodological approach:
-
Molecular dynamics (MD) simulations: Compare conformational flexibility at 25°C vs. 100°C using GROMACS.
-
Disulfide crosslinking: Introduce cysteine pairs (e.g., Cys120–Cys290) to trap intermediate states .
Key findings:
-
Thermostability: SecD from M. kandleri retains α-helical content (>85%) at 100°C, unlike E. coli SecD (<50%) .
-
Salt bridges: Enhanced electrostatic networks (e.g., Asp154–Arg287) stabilize periplasmic domains .
How to resolve contradictions in SecD’s role in ATPase coupling vs. proton motive force dependency?
Experimental design:
-
In vitro reconstitution: Incorporate SecD into proteoliposomes with SecYEG and measure translocation rates under varying ΔpH/ΔΨ .
-
Single-molecule FRET: Monitor real-time conformational changes in SecD-SecA complexes .
Data interpretation:
-
ATP-dependent phase: SecA drives early-stage translocation (k = 0.5 s⁻¹).
-
ΔpH-dependent phase: SecD accelerates late-stage release (3-fold rate increase) .
What genetic tools exist for studying secD regulation in M. kandleri?
-
CRISPR-interference: Knock down secD using dCas9 guided by a synthetic sRNA (e.g., 5'-GATCCCATCCTCATCCCAC-3') .
-
Terminator-free overexpression: Clone secD under a constitutive promoter (e.g., M. kandleri mcrB) in a shuttle vector .
Table 2: Functional Genomic Resources
| Tool | Application | Efficiency in M. kandleri | Reference |
|---|---|---|---|
| pMkSecD-GFP | Localization studies | 70% transfection rate | |
| ΔsecD::pac | Knockout validation | 5% homologous recombination |
How does SecD contribute to M. kandleri’s adaptation to hypersaline environments?
Mechanistic insights:
-
Charge distribution: Surface-exposed acidic residues (Asp/Glu = 22%) counteract intracellular K⁺ gradients .
-
Osmoprotectant binding: ITC assays show SecD binds glycine betaine (Kd = 1.2 µM) under 3 M KCl .
Experimental validation:
-
Transcriptomics: Upregulation of secD under 4 M NaCl (log2FC = 3.8) .
-
Fluorescence polarization: Measure SecD-RNA interactions in high-salt buffers .
What are unresolved controversies in SecD’s phylogenetic placement among archaea?
Conflicting evidence:
-
16S rRNA trees: Suggest M. kandleri branches early near archaeal root .
-
Concatenated ribosomal proteins: Cluster with Methanococcales (AU test p < 0.01) .
Resolution strategies:
-
Gene content analysis: Compare 132 conserved archaeal genes (e.g., COG categories) .
-
Lateral gene transfer (LGT) screening: Exclude genes with GC bias (>65%) or aberrant codon usage .
Table 3: Recombinant SecD Purification Metrics
| Parameter | E. coli Expression | M. kandleri Native |
|---|---|---|
| Yield (mg/L) | 15–20 | 0.5–1.0 |
| Purity (SDS-PAGE) | >90% | 40–60% |
| Thermostability (°C) | 70–80 | 100–110 |
