Part 1-BBa_K5532001
Name: gp17
Base Pairs: 1689 bp
Origin: T3 phage tail fiber protein (TFP) gp17 (NCBI Reference Sequence: NP_523342.1)
Usage and Biology
The tail fiber protein (TFP) gp17 of T3 phage is a critical component involved in the phage's ability to recognize and attach to its host bacterium, typically Escherichia coli (E. coli). The protein forms a trimeric structure that plays a key role in binding to the bacterial surface receptors, facilitating the subsequent steps of infection [1]. The tail fibers are responsible for the initial contact and irreversible binding to the host cell, which is a crucial determinant of the phage's host range and specificity [2].
TFP gp17 can be utilized in various biotechnological applications, including biosensors for detecting specific bacterial strains. Its high specificity and binding affinity make it an excellent candidate for developing diagnostic tools [2].
Cultivation, Purification, and SDS-PAGE
To obtain the gp17 (TFP) protein, we transformed the successfully constructed pET28a-gp17 plasmid into E. coli BL21 (DE3) cells for protein expression. After inducing protein expression by adding 1mM IPTG, the SDS-PAGE gel results showed that the gp17 (TFP) protein was successfully expressed in the samples with 1mM IPTG. Following protein induction, we collected the cells and lysed them. The His-tagged TFP protein was purified using nickel-affinity chromatography. The purified TFP protein was then analyzed by SDS-PAGE, and the results demonstrated that the TFP protein was successfully purified (Fig. 1).
Fig. 1 SDS-PAGE analysis of the expression and purification of gp17 (TFP) protein
Characterization/Measurement:
After purifying the gp17 (TFP) protein, we conjugated the gp17 (TFP) protein with synthesized gold nanoparticles (AuNPs) via electrostatic physical adsorption. Using a microplate reader, we measured the absorption peaks of the AuNPs before and after conjugation across the full wavelength spectrum. The results indicated that after conjugation with the TFP protein.
To evaluate whether the conjugated AuNP@TFP could detect E. coli, we incubated the conjugated AuNP@TFP with varying concentrations of E. coli at room temperature for 30 min. After incubation, the supernatant was collected and analyzed using smartphone photography. The results showed that as the bacterial concentration increased, the color of the supernatant became progressively lighter. This change in color indicated that AuNP@TFP could be used to detect E. coli (Fig. 2).
Fig. 2 UV-Vis Absorption Spectra of AuNPs@TFP and bacteria detection colorimetric analysis of AuNP@ TFP Conjugates
Part 2-BBa_K5532002
Name: tailspike
Base Pairs: 2067 bp
Origin: Salmonella phage CKT1 tailspike protein (TSP) tailspike (GenBank: UJP30002.1)
Usage and Biology
The tailspike protein (TSP) of Salmonella phage CKT1 is a crucial component in the infection mechanism of this bacteriophage. TSPs are part of the phage's tail structure and are responsible for recognizing and binding to specific receptors on the surface of the host bacterium. They exhibit polysaccharide depolymerase activity, which allows them to cleave the O-antigen moiety of the lipopolysaccharide (LPS) on the bacterial surface. This enzymatic activity facilitates the penetration of the bacterial cell wall, enabling the phage to inject its genetic material and initiate infection [3][4].
TSPs can be used in agricultural and food safety applications to control pathogenic bacteria such as Salmonella, thereby reducing the incidence of foodborne illnesses [3].
Due to their high specificity for certain bacterial strains or serotypes, TSPs can be utilized in diagnostic assays to detect and monitor bacterial infections. For instance, TSPs can be incorporated into biosensors to identify the presence of Salmonella in clinical or environmental samples [4].
Cultivation, Purification, and SDS-PAGE
During the construction phase, we amplified the tailspike gene and the linearized pET28a vector backbone using PCR. After confirming the correct band sizes via gel electrophoresis, we recovered the amplified gene and vector fragments from the gel. These fragments were then ligated through a method of homologous recombination. The ligation product was subsequently transformed into DH5α competent cells. After culturing, we selected single colonies and verified them using colony PCR and sequencing. Once we identified the correct plasmid clones through PCR and sequencing, we extracted the plasmids and transformed them into the BL21(DE3) expression strain for subsequent protein expression and purification. Then we induced protein expression by adding IPTG. Following induction, we used a His-Tag protein purification kit to purify the protein. SDS-PAGE results confirmed the successful induction by IPTG and the successful purification of the protein (Fig. 3).
Fig. 3 SDS-PAGE analysis of the expression and purification of plyV12(CBD) protein
Characterization/Measurement:
After purifying the tailspike (TSP) protein, we conjugated the TSP protein with synthesized gold nanoparticles (AuNPs) via electrostatic physical adsorption. The expected shift in the maximum absorption peak from 530 nm to 533 nm was confirmed using a microplate reader, indicating successful conjugation. Then we incubated varying concentrations of Salmonella with AuNP@TSP at room temperature for 30 min. Analysis of the supernatant using smartphone photography showed that higher bacterial concentrations resulted in a progressively lighter color of the supernatant, demonstrating that AuNP@TSP can be used to detect Salmonella (Fig. 4).
Part 3-BBa_K5532003
Name: plyV12
Base Pairs: 525 bp
Origin: Staphylococcus aureus phage plyV12 endolysin cell wall binding domain (CBD) (GenBank accession No. AAT01859.1)
Usage and Biology
Function: The cell wall binding domain (CBD) of the endolysin plyV12 is a critical component of the bacteriophage's lytic system. It specifically binds to the cell wall of Staphylococcus aureus (S. aureus), facilitating the enzymatic activity of the endolysin to degrade the bacterial cell wall peptidoglycan. This binding is highly specific and crucial for the targeted lysis of S. aureus cells, which enables the release of progeny phages [5].
The specificity of plyV12 for S. aureus can be utilized in diagnostic assays to detect the presence of this pathogen in clinical and environmental samples. This can aid in the rapid identification and monitoring of S. aureus infections [5]. Biocontrol in Food Safety: plyV12 can be applied in the food industry to control S. aureus contamination. Its use as a biocontrol agent can help reduce the incidence of foodborne illnesses caused by this pathogen [6].
Fig. 5 SDS-PAGE Analysis of the expression and purification of plyV12(CBD) protein