Part:BBa_K1965004
Au1:GvpA
This part was previously deposited in the registry as Part:BBa_K737016. We improved it’s sequence by adding the AU1 tag to the N-terminus and further characterized it by cloning it under the CMV promotor and expressing it in mammalian cells.
This part contains the coding sequence for the GvpA protein from the cyanobacterium Planktotrix rubescens. GvpA is the core protein of gas vesicles in cyanobacteria. It is a small (7–8 kDa) hydrophobic protein that forms the ribs of the gas vesicle wall [2]. In nature it interacts with GvpC, which attaches to the outer surface of the cyanobacterial gas vesicle [3] and strengthens its structure [1].
We used the gas vesicle forming proteins to improve the sensitivity of HEK293 cells to ultrasound stimulation, as shown in (1).
Schematic presentation of a cell expressing mechanosensitive channels and gas vesicle-forming proteins. When exposed to mechanical stimuli, the gas vesicles interact with the cytoskeleton, resulting in activation of mechanosensitive channels on the cell membrane.
Characterisation
Expression of both GvpA and GvpC was determined by western blotting (2) and co-localization was observed by confocal microscopy (3)
Expression of GvpC (A) and GvpA (B) protein was determined by Western blot using anti-FLAG (A) and anti-AU1 (B) antibodies. Expected sizes (marked with *) are 22,5 kDa for GvpC and 8,5 kDa for GvpA. HEK293T cells were transfected with plasmids, encoding gas vesicle-forming proteins GvpA and GvpC. 48 h after transfection cells were collected, lysed and total protein concentration was measured. 50ng of proteins were loaded on SDS page gels. After separation by size, proteins were transferred to nitrocellulose membrane by western blot. Membranes were then immunoblotted with anti-FLAG or anti-AU1 antibodies.
HEK293T cells were transfected with plasmids, encoding gas vesicle-forming proteins GvpA and GvpC. 24 h after transfection cells were fixed, permeabilized and immuno-stained with anti-FLAG (upper row) and anti-AU1 (bottom row). Both GvpA and GvpC are localized in cytosol. Co-localization is depicted in the overlay picture (far right, upper row).
In order to ensure that gas vesicles were not toxic to mammalian cells, a viability assay was performed. Viability of transfected cells overexpressing GvpA and GvpC was determined using the trypan blue dye, which selectively stains only dead cells. 4 shows that the viability of cells was not altered when expressing the proteins for formation of gas vesicles.
HEK293 cells were transfected with GvpA and/or GvpC. 24 h after the transfection the cells were stained with the trypan blue dye and their viability was determined using the Countess™ automated cell counter.
Ultrasound stimulation
After confirming GvpA and GvpC expression in HEK293 cells, we stimulated the transfected cells with ultrasound. Our experimental setup included an in-house built hardware MODUSON connected to unfocused transducer Olympus V318-SU. To monitor cell response in situ and in real time we used standard ratiometric fluorescent calcium indicators Fura Red, AM and Fluo-4, AM, which can be easily detected with confocal microscopy.. When activated, mechanosensitive channels open, leading to calcium influx, which in turn binds the fluorescent calcium indicators. The indicator conformation changes upon calcium binding, resulting in an increase or a decrease of fluorescence.
The HEK293 cells, expressing gas vesicle-forming proteins, were not responsive to ultrasound stimulation at mild ultrasound conditions (voltage 450Vpp), but exhibited increased sensitivity to ultrasound stimulation at higher voltages (900Vpp) even in the absence of exogenous mechanosensitive channels 5 .This phenomenon is most likely due to activation of endogenous mechanosensitive channels in mammalian cells.
(A) Presentation of stimulation sequences for 900 Vpp (red) and 450 Vpp (grey) Vpp and (B) signal parameters used for stimulation.
(C) Genetically encoded gas vesicle-forming proteins increased cell response at high-power (900 Vpp) in comparison to low-power ultrasound (450 Vpp).
In an attempt to improve calcium influx, we co-transfected HEK293 cells with plasmids encoding the MscS channel (BBa_K1965000) and gas vesicle-forming proteins. The voltage of ultrasound stimulation was decreased to 450 Vpp as higher voltage also causes calcium influx in cells expressing only gas vesicle-forming proteins (5). By decreasing the voltage of ultrasound stimulation we successfully showed that only cells expressing both the MscS channel and the gas vesicle-forming proteins were activated as a result of ultrasound stimulation. (6).
(A) Schematic presentation of the stimulation sequence and (B) signal parameters used for stimulation.
(C) Co-expression of mechanosensitive channels and gas vesicle-forming proteins increased sensitivity to ultrasound stimulation in comparison to the cells without exogenous mechanosensitive channels.
References
[1]Hayes, P. K., Buchholz, B., & Walsby, a E. (1992). Gas vesicles are strengthened by the outer-surface protein, GvpC. Archives of Microbiology, 157(3), 229–234. https://doi.org/10.1007/BF00245155[2]Hayes, P. K., Walsby, A. E., & Walker, J. E. (1986). Complete amino acid sequence of cyanobacterial gas-vesicle protein indicates a 70-residue molecule that corresponds in size to the crystallographic unit cell. The Biochemical Journal, 236(1), 31–6. https://doi.org/10.1042/BJ2360031
[3]Walsby, a E., & Hayes, P. K. (1988). The minor cyanobacterial gas vesicle protein, GvpC, is attached to the outer surface of the gas vesicle. Journal of General Microbiology, 134(10), 2647–2657. https://doi.org/10.1099/00221287-134-10-2647
Sequence and Features
- 10COMPATIBLE WITH RFC[10]
- 12COMPATIBLE WITH RFC[12]
- 21COMPATIBLE WITH RFC[21]
- 23COMPATIBLE WITH RFC[23]
- 25COMPATIBLE WITH RFC[25]
- 1000INCOMPATIBLE WITH RFC[1000]Illegal BsaI.rc site found at 172
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