Expression, purification and folding of native like mitochondrial carrier proteins in lipid membranes
Bibliographic record
Abstract
Mitochondrial Carrier Family proteins (MCFs) are located in the mitochondrial inner membrane and play essential roles in various cellular processes. Due to the relatively low abundance of many members of the family, in vitro structure and function determination of most MCFs require over-expression and purification of recombinant versions of these proteins. In this study, we report on a new method for overexpression of MCFs in Escherichia coli (E. coli) membranes, efficient purification of native-like proteins, and their reconstitution in mitochondrial inner membrane lipid mimics. cDNAs of Uncoupling Protein 4 (UCP4), Adenine Nucleotide Translocase (ANT) and Phosphate Translocase (PiT) were subcloned into the pET26b (+) expression vector such that fusion proteins with a short N-terminal pelB leader sequence and a six-histidine tag were produced to target the proteins toward the inner membrane of E. coli and facilitate affinity purification, respectively. Utilizing a modified autoinduction method, these proteins were overexpressed and extracted from the membrane of E. coli BL21 (DE3) and two modified strains, E. coli BL21 C43 (DE3) and E. coli BL21 Lobstr (DE3), in high yields. The proteins were then purified by immobilized metal affinity chromatography as monomers. Purity, identity, and concentration of the eluted monomers were determined by semi-native SDS-PAGE, Western blotting and mass spectrometry, and a modified Lowry assay, respectively. Cleavage of the pelB leader sequence from proteins was verified by mass spectrometric analysis. The purified proteins, surrounded by a shell of bacterial membrane lipids, were then reconstituted from the mild non-denaturing octyl glucoside (OG) detergent into phospholipid liposomes. Monomeric UCP4 spontaneously self-associated to form stable tetramers in lipid membranes, which is consistent with our previous studies. However, PiT and ANT remained dominantly monomeric in both detergent and liposome milieus, as detected by a combination of spectroscopic and electrophoretic methods. Native-like helical conformations of proteins were then confirmed by circular dichroism spectroscopy. Overall, this study demonstrates that targeting mitochondrial carrier family proteins to E. coli membranes provides an effective expression system for producing this family of proteins for biophysical studies.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".