Part:BBa_K4387986

Monovalent nanobody expression with the HlyA secretion signal (VHH#2B)

The hemolysin A secretion machinery is a one-step secretion system (T1SS), originally isolated from uropathogenic E. coli strains. [1] It comprises three main peptides, the inner membrane proteins HlyB and HlyD, and the outer membrane protein TolC. Together, these three proteins build a continuous channel through which originally the HlyA toxin is secreted in a one-step manner. Scientists have identified the secretion signal and were able to secrete various proteins of different sizes with this secretion machinery. [1]

This composite part contains an anti-TNFα nanobody fused to a myc-tag and the HlyA-tag required for the secretion with the hemolysin A secretion system BBa_K4387979. The expression of the monovalent nanobody is under the control of the inducible pBAD system, followed by the T7 RBS. The myc-tag was required for the characterization of the secretion and functionality of the nanobody. The nanobody inserted in this part is the monovalent candidate VHH#2B BBa_K4387996. [2]

Sequence and Features

Assembly Compatibility:

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

  Illegal NheI site found at 1205
  
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal BglII site found at 1650
  Illegal BglII site found at 2229
  Illegal BamHI site found at 1144
  
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal AgeI site found at 979
  
• 1000
  COMPATIBLE WITH RFC[1000]

Characterization

Western blot

Figure 1:Double transformed E. coli MC1061 were induced by arabinose and incubated at 37°C overnight. Anti-myc antibodies were used in this Western blot to stain secreted nanobodies in the bacterial supernatant. Nb1 = VHH#2B

We double transformed the common lab strain E. coli MC1061 with the high copy plasmid containing this composite part required for induced nanobody expression, and the medium copy number plasmid containing the composite part BBa_K4387987 required for the secretion system. Liquid overnight cultures of the transformed strain were grown and induced by adding the appropriate amount of arabinose. On the next day, the cells were centrifuged, and the supernatant was run on a gel. To see if nanobodies of the correct size have been secreted, we conducted a Western blot detecting the myc-tag fused to the nanobodies with anti-myc antibodies (Figure 1).

As seen in figure 1, we received a band, labelled as N1, with the size of approximately 45 kDa which fits the expected size of the nanobody candidate VHH#2B together with the myc-tag and HlyA-tag. We can therefore assume that the bacteria were able to secrete whole nanobodies.

Figure 2: ELISA comparing the TNFα-binding capabilities of purified vs secreted monovalent and bivalent nanobodies obtained from MC1061

ELISA

To proof that the secreted nanobodies not only have the correct size but are also able to elicit their TNFα-binding abilities, we performed an ELISA (Figure 2). Adalimumab, a monoclonal anti-TNFα antibody already used in the clinics to treat IBD patients, served as a positive control (wells D1-2), and a sybody against a membrane protein was the negative control (wells D3-4). We could show that the transformed E. coli MC1061 is able to secrete functional anti-TNFα nanobodies. Successful binding of nanobody VHH#2B is seen in wells A1-2. The next two wells A3-4 show the binding capability of the purified nanobody VHH#2B, indicating that secretion did not have a negative influence on the folding of the nanobody and the additional HlyA-tag does not hinder the nanobody from binding TNFα.

Alternative Chassis

We also double transformed the probiotic strain E. coli Nissle 1917 with both plasmids and performed the same experiments as described above. Figure 3 shows the successful secretion of nanobody VHH#2B and figure 4 the binding capability of the secrete monovalent nanobody to TNFα.

---Figure 3 and 4---

References

• [1] Ruano-Gallego, D., Fraile, S., Gutierrez, C. et al. Screening and purification of nanobodies from E. coli culture supernatants using the hemolysin secretion system. Microb Cell Fact 18, 47 (2019). https://doi.org/10.1186/s12934-019-1094-0
• [2] Silence, Karen, Lauwereys, Marc, De Haard, Hans, et al. "Single domain antibodies directed against tumour necrosis factor-alpha and uses therefor", Int. Publication Number: WO 2004/041862 A2, 21 May 2004