SgsE | CFP


Designed by: Timo Wolf   Group: iGEM11_Bielefeld-Germany   (2011-09-10)

Fusion Protein of S-Layer SgsE and mCerulean


Fusion Protein of S-Layer SgsE and mCerulean

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 (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.

This fluorescent S-layer fusion protein is used to characterize purification methods and the S-layer's ability to self-assemble on surfaces. It is also possible to use the characteristic of mCerulean as a pH indicator or FRET donor (Kainz et al., 2010).

Important parameters

Experiment Characteristic Result
Expression (E. coli) Localisation Inclusion body
Compatibility E. coli KRX and BL21(DE3)
Induction of expression expression of T7 polymerase + IPTG or lactose
Specific growth rate (un-/induced) 0.127 h-1 / 0.229 h-1
Doubling time (un-/induced) 5.45 h / 3.02 h
Purification Molecular weight 110.1 kDa
Theoretical pI 5.63
Excitation / emission 435 / 477 nm
Immobilization behaviour Immobilization time 4 h

Sequence and Features

Assembly Compatibility:
  • 10
  • 12
  • 21
    Illegal BglII site found at 167
    Illegal BglII site found at 1022
  • 23
  • 25
    Illegal NgoMIV site found at 76
    Illegal AgeI site found at 3121
  • 1000
    Illegal BsaI site found at 1657

Expression in E. coli

The SgsE gene under the control of a T7 / lac promoter (BBa_K525303) was fused to mCerulean (BBa_J18930) using Freiburg BioBrick assembly for characterization experiments.

The SgsE|mCerulean fusion protein was overexpressed in E. coli KRX after induction of T7 polymerase by supplementation of 0.1 % L-rhamnose and 1 mM IPTG using the autinduction protocol by Promega.

Figure 1: Growth curve of E. coli KRX expressing the fusion protein of SgsE and mCerulean with and without induction, cultivated at 37 °C in autoinduction medium with and without inductor, respectively. A curve depicting KRX wildtype is shown for comparsion. After induction at approximately 4 h the OD600 of the induced K525306 visibly drops when compared to the uninduced culture. Both cultures grow significantly slower than KRX wildtype.
Figure 2: RFU to OD600 ratio of E. coli KRX expressing the fusion protein of Sgse and mCerulean with and without induction. A curve depicting KRX wildtype is shown for comparsion. After induction at approximately 4 h the RFU to OD600 ratio starts to rise in the induced culture. Compared to the uninduced culture the ratio is roughly 34 times higher at its highest point but starts to drop during the cultivation due to degradation of the fusion protein. The KRX wildtype shows no variation in the RFU to OD600 ratio.


Expression of S-layer genes in E. coli

  • Medium: LB medium supplemented with 20 mg L-1 chloramphenicol
    • For autoinduction: Cultivations in LB-medium were supplemented with 0.1 % L-rhamnose and 1 mM IPTG as inducer and 0.05 % glucose

Measuring of mCerulean

  • Take at least 500 µL sample for each measurement (200 µL is needed for one measurement) so you can perform a repeat determination
  • Freeze biological samples at -80 °C for storage, keep cell-free at 4 °C in the dark
  • To measure the samples thaw at room temperature and fill 200 µL of each sample in one well of a black, flat bottom 96 well microtiter plate (perform at least a repeat determination)
  • Measure the fluorescence in a platereader (we used a Tecan Infinite® M200 platereader) with following settings:
    • 20 sec orbital shaking (1 mm amplitude with a frequency of 87.6 rpm)
    • Measurement mode: Top
    • Excitation: 433 nm
    • Emission: 475 nm
    • Number of reads: 25
    • Manual gain: 100
    • Integration time: 20 µs


Kainz B, Steiner K, Möller M, Pum D, Schäffer C, Sleytr UB, Toca-Herrera JL (2010) Absorption, Steady-State Fluorescence, Fluorescence Lifetime, and 2D Self-Assembly Properties of Engineered Fluorescent S-Layer Fusion Proteins of Geobacillus stearothermophilus NRS 2004/3a, Biomacromolecules 11(1):207-214.

Sleytr UB, Huber C, Ilk N, Pum D, Schuster B, Egelseer EM (2007) S-layers as a tool kit for nanobiotechnological applications, FEMS Microbiol Lett 267(2):131-144.