Difference between revisions of "Part:BBa K3885151"

Revision as of 17:53, 21 October 2021

ssrA

The ssrA tag, an 11-aa peptide added to the C terminus of proteins stalled during translation, targets proteins for degradation by ClpXP and ClpAP.ClpX interacts with residues 9–11 at the C terminus of the tag, whereas ClpA recognizes positions 8–10 in addition to residues 1–2 at the N terminus.

Characterization

ZJUT-China team using degraded tag ssrA,refined two parts:deGFP-ssrA and tetR-ssrA.

1.Information supplementary of deGFP-ssrA.

'''Summary:''' According to the lectures, we learned that the degradation rate of eGFP-ssrA could be measured. In the cell-free system, protein degradation by clpXP is described by a zeroth order chemical kinetic.In protein substrates (eGFP), ClpX recognizes ssrA--a specific C-terminal degradation tag, proceeds to unfold stable tertiary structure in the protein, and then spools or translocates the unfolded polypeptide chain into a sequestered proteolytic compartment in ClpP for degradation into small peptide fragments. As part of iGEM18_William_and_Mary, ZJUT-China assessed the degradation rate of different eGFP [https://parts.igem.org/Part:BBa_K2680550 (Part:BBa_K2680550)]by adding different concentrate of plasmid P70-ClpXP [https://parts.igem.org/Part:BBa_K3885203 (Part:BBa_K3885203)]based on the reference. We hope this will enhance further modeling and experiments.

Methodology

There are two methods to express clpxp protein: co-expression and pre-expression.Accelerated protein degradation can be achieved by co-expression of P70a-ClpXP, by adding protein to a cell-free system pre-incubated with P70a-ClpXP for an hour or by adding dilutions of pre-expressed ClpXP (P70a-ClpXP, 3nM). Different methods can provide different rates of protein degradation, ranging from 9.3 nM/min to 250 nM/min. By expressing ClpXP, protein synthesis can be adjusted to an appropriate rate[1].

Results

Figure 1 Degradation rate of deGFP upon different expression methods of ClpXP.

The degradation rate of eGFP-ssrA only using the endogenous ClpXP has been determined by an assay, which is achieved by measuring the kinetics after adding pure His-eGFP-ssrA (5μM) to the Cell-Free system.

Analysis

As shown in the figure above, the higher the concentration of ClpXP, the faster the degradation of eGFP-ssrA. Meanwhile, according to the table, when ClpXP with the same concentration was added, eGFP degradation rate in pre-expression was from 6.5 nM/min to 256 nM/min, while in co-expression, eGFP degradation rate was from 9.3 nM/min to 128 nM/min. It can be concluded that pre-expression is more conducive to eGFP protein degradation than co-expression.

1.Improvement of tetR-ssrA.

Usage and Biology

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Figure 1. Schematic of hydrolysis by ClpXP protein.

To ensure the normal operation of the Cell-Free system, an adjustable protein degradation mechanism is crucial. It is degraded by ClpXPAAA+ protease in Escherichia coli . The protein must contain a degradation tag in order to be recognized by our cell-free system .

Characterization

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Figure 2. Schematic of gene circuits and kinetics of tetR inhibition in the Cell-Free system.
(A) The gene circuits contains three parts, sigma 28 activates promoter P28 to express tet repressor with ssrA tag, which inhibits the expression of deGFP.
(B) The gene circuits contains an additional part P70-ClpXP that makes the tetR repressor degrade, and degfp expresses.
(C) Group 1 carried tetR without ssrA and ClpXP; Group 2 carried tetR with ssrA; Group 3 didn't carry tetR as positive control; Group 4 carried tetR with ssrA and ClpXP in comparison with Group 1.

In Figure 2. C, the highest red line ( Group 3) contains only P70a-σ28 and P28-tetO-deGFP plasmids, thus expressing deGFP with high fluorescence intensity and serving as a positive control. The second highest purple line ( Group 4) with P70a-ClpXP can degrade tetR repressor with ssrA tag, eliminate its inhibition of deGFP expression in downstream of the gene circuits, and increase fluorescence intensity. The green line at the bottom of Figure 2. C ( Group 1) indicates that the tetR repressor without ssrA tag cannot be degraded by ClpXP protein, in contrast to Group 4, indicating that the ssrA degradation tag is functional. The blue line ( Group 2) is at the bottom of Figure 2. C showed low fluorescence intensity, which was used as a negative control to indicate that the addition of tag did not affect the inhibition of tetR.
Therefore, we gave the tetR a new function and improved this part.
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Sequence and Features

Assembly Compatibility:

10
COMPATIBLE WITH RFC[10]
12
COMPATIBLE WITH RFC[12]
21
COMPATIBLE WITH RFC[21]
23
COMPATIBLE WITH RFC[23]
25
COMPATIBLE WITH RFC[25]
1000
COMPATIBLE WITH RFC[1000]

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 ZJUT-China team using degraded tag ssrA,refined two parts:deGFP-ssrA and tetR-ssrA.
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 .Information supplementary of deGFP-ssrA.