Designed by: Nicolas Bayer   Group: iGEM21_TU_Kaiserslautern   (2021-10-06)

mCerulean, MocloMania B4


This part codes for the cyan fluorescent protein mCerulean.[1] The protein was originally derived from the green fluorescent protein GFP which was first isolated from the bioluminescent jellyfish Aequorea victoria in 1962.[2] It can be fused to a protein of interest, making it accessible to easy and non-invasive screening opportunities that involve fluorescence monitoring, such as fluorescence spectroscopy or microscopy.[3]

size 26.8 kDa

function fluorescent tag

excitation wavelength 435 nm

emission wavelength 477 nm

cloning position B4

plasmid backbone pAGM1299


We were able to successfully clone this basic part into its respective L0 plasmid backbone and to confirm the integrity of the L0 construct via restriction digest and gel electrophoresis, see Figure 1. Furthermore, we were able to include it into a L1 construct, proving its correct adaptation towards MoClo assembly, see Figure 2.

Several different L1 constructs assembled with L0_mCerulean_B4 have been successfully transfected into Leishmania, resulting in recombinant protein expression that could be observed after immunostaining on western blot.

Looking at Figure 3, we see that both constructs that employ L0_mCerulean_B4, namely 2 | L1_sAP_RBD_mCerulean_Strep8His and 3 | L1_sAP_RBD_mCerulean_GST, show definite protein bands when stained against the SARS-CoV-2 receptor binding domain. As both constructs contain the sAP secretion tag, we can see that protein expression is detected both in the cell lysate P+ as well as in the culture supernatant S+. In silico calculations predict construct 2 to weigh about 50 kDa and construct 3 around 80 kDa. Taking into consideration small deficiencies in gel density due to high percentage of acrylamide, both constructs' upper bands can be attributed to that respective size. However, a smaller band, running at around 28 kDa can be observed for both constructs, but exclusively in the cell culture supernatant. This leads to the hypothesis of extracellular cleavage processes occurring after secretion of the fusion protein into the culture medium. For more information on this, please consult the sAP secretion tag part site.

Out of all the L1 constructs employing L0_mCerulean_B4, so far L1_sAP_RBD_mCerulean_GST has been successfully purified. Even tho this purification didn't yield substantial amounts of intact fusion protein, we still tried to investigate the activity of the purified RBD by incubating human HEK cell lines overexpressing the ACE2 recpetor with the RBD eluate and observing fluorescence via fluorescence microscopy, see Figure 4. The overexpressing cell line is abbreviated as HEK+. As a negative control we used HEK 293T cells that don’t express ACE2, HEK-. For both cells, the nucleus was visualized with the help of DAPI. Additionally, the cells were treated with a solution that extends the emission/extinction of the fluorophores, ProLong Glass Antifade Mountant.

  • Figure 4 | Fluorescence microscopy HEK-cells transfected with L1_sAP_RBD_mCerulean_GST
    A-C | HEK--cells | DAPI nucleus stain | incubation with RBD_mCerulean_TEV_GST
    D-F | HEK+-cells | DAPI nucleus stain | incubation with RBD_mCerulean_TEV_GST
    emission | 435 nm
    extinction | 477 nm

Due to the visible disintegration of the nucleus in many of the HEK+ cells, it is evident that they are mutants and therefore not as fit as the HEK-- cells. The mCerulean fluorophore has the same excitation wavelength as DAPI, which makes it difficult to distinguish them from one another. Nevertheless, a slight shimmer around the HEK+ cells is visible which is not apparent in the HEK- cells. That could indicate the binding of our RBD_mCerulean fusion protein to the ACE2 receptors on the cells' outer membrane. Having mCerulean and DAPI fluorescence spectra overlapping is an unanticipated issue which we plan to resolve by introducing additional fluorescent tags into our library, covering a broader range of excitation and emission wavelengths.

The MocloMania collection

This basic part is part of the MocloMania collection, the very first collection of genetic parts specifically designed and optimized for Modular Cloning assembly and recombinant protein expression in the protozoan parasite Leishmania tarentolae.

Are you trying to express complexly glycosylated proteins? Large antibody side chains? Human proteins that require accurate post-translational modification? Then Leishmania might be just the right organism for you! Leishmania tarentolae’s glycosylation patterns resemble those of human cells more closely than any other microbial expression host, while still delivering all the benefits of microbial production systems like easy transfection and cultivation.[4] So instead of relying on mammalian cell lines, try considering Leishmania as your new expression host of choice!

Our MocloMania collection will allow you to easily modify your protein of choice and make it suitable for downstream detection and purification procedures - all thanks to the help of Modular Cloning. This cloning system was first established by Weber et al. in 2011 and relies on the ability of type IIS restriction enzymes to cut DNA outside of their recognition sequence, hereby generating four nucleotide overhangs.[5] Every basic part in our collection is equipped with a specified set of overhangs that assign it to its designated position within the reading frame. These so-called cloning positions are labelled B2-B5 from upstream to downstream. By filling all positions with the basic parts of your choice, you can easily generate variable genetic constructs that code for the fusion protein of your desire.

We furthermore provide a specifically domesticated Leishmania expression vector, named weird_plex, which will package your fusion construct into a functional transcriptional unit that is optimized for high expression in Leishmania.

The best part? Because of the type IIS restriction properties and the specifity of the generated overhangs, restriction and ligation of your construct can all happen simultaneously in a simple one-step, one-pot reaction. This will safe you a lot of time and frustration in your cloning endeavours!

Do we have your attention? In the table below you can find some basic information on how our cloning system, along with most other MoClo systems, is set up. Please feel free to check out our wiki to find more information on Leishmania and Modular Cloning as well as to understand how this basic part integrates into our part collection. See you there!

MOCLO | Important nomenclature and parameters
Level What does this level contain? antibiotic resistance Enzyme used for ligation
L0 The foundation to every MoClo construct which are basic genetic units, such as coding sequences, promoters, terminators spectinomycin BbsI
L1 Several L0 parts assembled into a functional transcriptional unit, e.g. consisting of promoter, coding region and terminator ampicillin BsaI
L2 Multiple transcriptional units added into one multi-gene construct, e.g. a protein of interest fused to a resistance cassette kanamycin BbsI

Sequence and Features

Assembly Compatibility:
  • 10
  • 12
  • 21
  • 23
  • 25
    Illegal NgoMIV site found at 679
  • 1000

Reference Literature

  1. R Heim, D C Prasher, R Y Tsien, "Wavelength mutations and posttranslational autoxidation of green fluorescent protein", Proceedings of the National Academy of Sciences Dec 1994, 91 (26) 12501-12504; DOI: 10.1073/pnas.91.26.12501
  2. Shimomura, O., Johnson, F.H. and Saiga, Y. (1962) Extraction, Purification, and Properties of Aequorin, a Bioluminescent Protein from the Luminous Hydromedusan, Aequorea. Journal of Cellular and Comparative Physiology, 59, 223-239.
  3. M.A. Rizzo, D.W. Piston High-contrast imaging of fluorescent protein FRET by fluorescence polarization microscopy Biophys. J., 88 (2005), pp. L14-L16
  4. Langer T, Corvey C, Kroll K, Boscheinen O, Wendrich T, Dittrich W. Expression and purification of the extracellular domains of human glycoprotein VI (GPVI) and the receptor for advanced glycation end products (RAGE) from Rattus norvegicus in Leishmania tarentolae. Prep Biochem Biotechnol. 2017 Nov 26;47(10):1008-1015. doi: 10.1080/10826068.2017.1365252. Epub 2017 Aug 31. PMID: 28857681.
  5. Weber E, Engler C, Gruetzner R, Werner S, Marillonnet S (2011) A Modular Cloning System for Standardized Assembly of Multigene Constructs. PLoS ONE 6(2): e16765.
biologycyan fluorescent protein
emission435 nm
excitation477 nm