Part:BBa_K525123

S-layer cspB from Corynebacterium glutamicum with lipid anchor and PT7 and RBS

S-layers (crystalline bacterial surface layer) are crystal-like layers consisting of multiple protein monomers and can be found in various (archae-)bacteria. They constitute the outermost part of the cell wall. Especially their ability for self-assembly into distinct geometries is of scientific interest. At phase boundaries, in solutions and on a variety of surfaces they form different lattice structures. The geometry and arrangement is determined by the C-terminal self assembly-domain, which is specific for each S-layer protein. The most common lattice geometries are oblique, square and hexagonal. By modifying the characteristics of the S-layer through combination with functional groups and protein domains as well as their defined position and orientation to eachother (determined by the S-layer geometry) it is possible to realize various practical applications ([http://onlinelibrary.wiley.com/doi/10.1111/j.1574-6968.2006.00573.x/full Sleytr et al., 2007]).

Usage and Biology

S-layer proteins can be used as scaffold for nanobiotechnological applications and devices by e.g. fusing the S-layer's self-assembly domain to other functional protein domains. It is possible to coat surfaces and liposomes with S-layers. A big advantage of S-layers: after expressing in E. coli and purification, the nanobiotechnological system is cell-free. This enhances the biological security of a device.

The S-layer of C. glutamicum is characterized by a hexagonal lattice symmetry. Attachment between S-layer and cell wall was found to be due to the hydrophobic carboxy-terminus of the PS2 protein [http://www.sciencedirect.com/science/article/pii/S016816560400241X Hansmeier et al., 2004]).

Important parameters

Experiment	Characteristic	Result
Expression (E. coli)	Localisation	cell membrane
	Compatibility	E. coli KRX
	Inductor for expression	L-rhamnose for induction of T7 polymerase
	Specific growth rate (un-/induced)	0.245 h^-1 / 0.093 h^-1
	Doubling time (un-/induced)	2.82 h / 7.42 h

Sequence and Features

Assembly Compatibility:

10
COMPATIBLE WITH RFC[10]
12
COMPATIBLE WITH RFC[12]
21
INCOMPATIBLE WITH RFC[21]
Illegal BamHI site found at 1334
Illegal XhoI site found at 161
Illegal XhoI site found at 779
23
COMPATIBLE WITH RFC[23]
25
COMPATIBLE WITH RFC[25]
1000
INCOMPATIBLE WITH RFC[1000]
Illegal BsaI.rc site found at 1313
Illegal SapI site found at 560
Illegal SapI site found at 772
Illegal SapI site found at 1320

Expression in E. coli

For characterization the CspB gen was fused with a monomeric RFP (BBa_E1010) using Gibson assembly.

The CspB|mRFP fusion protein was overexpressed in E. coli KRX after induction of T7 polymerase by supplementation of 0,1 % L-rhamnose using the autinduction protocol from promega.

Figure 1: Growthcurve of E. coli KRX expressing the fusion protein of CspB and mRFP with and without induction, cultivated at 37 °C in autoinduction medium with, respectively, without inductor. A curve depicting KRX wildtype is shown for comparsion. After induction at approximately 6 h the OD₆₀₀ of the induced K525123 visibly drops when compared to the uninduced culture. While the induced culture grow significantly slower than KRX wildtype the uninduced seems to be unaffected.

Figure 2: RFU to OD₆₀₀ ratio of E. coli KRX expressing the fusion protein of CspB and mRFP with and without induction. A curve depicting KRX wildtype is shown for comparsion. After induction at approximately 6 h the RFU to OD₆₀₀ ratio starts to rise in the induced culture. Compared to the uninduced culture the ratio is roughly eight times higher. Most likely due to basal transcription the RFU to OD₆₀₀ ratio of the uninduced culture starts to rise after 12 hours. The KRX wildtype shows no variation in the RFU to OD₆₀₀ ratio.

Identification and localisation

After a cultivation time of 18 h the mRFP|CspB fusion protein has to be localized in E. coli KRX. Therefor a part of the produced biomass was mechanically disrupted and the resulting lysate was wahed with ddH₂O. From the other part the periplasm was detached by using a osmotic shock. The existance of fluorescene in the periplasma fraction, showed in fig. 3, indicates that Brevibacterium flavum TAT-signal sequence is at least in part functional in E. coli KRX.

The S-layer fusion protein could not be found in the polyacrylamide gel after a SDS-PAGE of the lysate. This indicated that the fusion protein intigrates into the cell membrane with its lipid anchor. For testing this assumption the washed lysate was treted with ionic, nonionic and zwitterionic detergents to release the mRFP|CspB out of the membranes.

The existance of flourescence in the detergent fractions and the non-existancing fluorescence in the wash fraction confirm the hypothesis of an insertion into the cell membrane (fig. 3). An insertion of these S-layer proteins might stabilize the membrane structure and increase the stability of cells against mechanical and chemical treatment. A stabilization of E. coli expressing S-lyer proteins was discribed by Lederer et al., (2010).

An other important fact is, that there is actually mRFP fluorescence measurable in such high concentrated detergent solutions. The S-layer seems to stabilize the biologically active conformation of mRFP.

In comparison with the mRFP fusion protein of K525121, wich has a TAT-sequence, a minor relative fluorescence per OD₆₀₀ in all cultivation and detergent fractions was detected (fig. 3). Together with the decreasing RFU/OD₆₀₀ after 12 h of cultivation (fig. 2) indicates this rusults in a postive effect of the TAT-sequence on the protein stability.

Figure 3: Fluorescence pro OD₆₀₀ progression of the mRFP(BBa_E1010)/CspB fusion protein initiating with the cultivation fractions up to the detergent fractions of the seperate denaturations. Cultivations were carried out in autoinduction medium at 37 ˚C. The cells were mechanically disrupted and the resulting biomass was wahed with ddH₂O and resuspendet in the respective detergent. The used detergent acronyms stand for: SDS = 10 % sodium dodecyl sulfate; UTU = 7 M urea and 3 M thiourea; U = 10 M urea; NLS = 10 % n-lauroyl sarcosine; 2 % CHAPS = 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate.