Part:BBa_K525222

S-layer cspB from Corynebacterium halotolerans

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.

Important parameters

Experiment	Characteristic	Result
Expression (E. coli)	Localisation	Cell membrane
	Compatibility	E. coli KRX
	Induction of expression	L-rhamnose for induction of T7 polymerase
	Specific growth rate (un-/induced)	0.245 h-1 / 0.109 h-1
	Doubling time (un-/induced)	2.83 h / 6.33 h

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal BglII site found at 1103
  Illegal XhoI site found at 559
  
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal NgoMIV site found at 226
  Illegal NgoMIV site found at 1315
  Illegal AgeI site found at 217
  Illegal AgeI site found at 458
  Illegal AgeI site found at 505
  
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI site found at 907
  Illegal BsaI.rc site found at 214
  Illegal BsaI.rc site found at 592
  Illegal BsaI.rc site found at 994
  

Expression in E. coli

The CspB gen was fused with a monomeric RFP (BBa_E1010) using [http://2011.igem.org/Team:Bielefeld-Germany/Protocols#Gibson_assembly Gibson assembly] for characterization.

The mRFP|CspB fusion protein was overexpressed in E. coli KRX after induction of T7 polymerase by supplementation of 0,1 % L-rhamnose using the [http://2011.igem.org/Team:Bielefeld-Germany/Protocols/Downstream-processing#Expression_of_S-layer_genes_in_E._coli 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 K525222 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 five 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. Then the lysate was treted with ionic, nonionic and zwitterionic detergents to release the CspB|mRFP out of the membranes, if it intigrates. From the other part of the cells the periplasm was detached by using a osmotic shock.

The fluorescence in all cultivation fractions plus the fluorescence in the lysis und wash fraction shows that the fusion protein is water soluble and sediment not during centrifugation. Together with the absence of flourescence in the detergent fractions verifies that the fusion protein is not integrated into the cell membrane (fig. 3) and is not present as inclusion body.

In comparison with the mRFP fusion protein of ???, wich has a lipid anchor, a minor relative fluorescence per OD₆₀₀ in all cultivation and detergent fractions was detected (fig. 3). Together with the decreasing RFU/OD₆₀₀ after 14 h of cultivation (fig. 2) indicates this rusult a postive effect of the lipid anchor 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.

MALDI TOF analysis was used to identify the location of the fusion protein in different fractions. Fractions of medium supernatant after cultivation, periplasmatic isolation, cell lysis and following denaturation in 6 M urea were loaded onto a SDS_PAGE. After denaturation with 6 M urea the remaining pellet (after centrifugation 15,000 g for 30 min) was washed with 2 % (v/v) Triton X-100, 2 % SDS (w/v). This fraction was also loaded onto the SDS-PAGE and fragments of the gel were measured with MALDI TOF.

Figure 4: SDS-PAGE of CspB/mRFP (BBa_E1010) fusion protein. Lanes are fractions of medium (M), periplasmatic isolation (PP), cell lysis (L), denaturation (D) and wash with Triton X-100 (T). Used Marker is PageRuler ^TM Prestained Protein Ladder SM0671. Marked regions were cut out and prepared for MALDI TOF analysis.

The following table shows the sequence coverage (in %) of our measurable gel samples with the amino acid sequence of fusion protein CspB/mRFP (BBa_E1010).