Origin of Antisperm Antibodies
During the 20th century, several cases of infertile men and women were observed. At the time, the reasons for this sterility were elusive. Eventually, researchers discovered that that one cause was the result of the production of antisperm antibodies (ASA) . These antibodies can be produced by either of women or men against spermatozoa, leading to immotility of the spermatozoa and subsequent infertility. ASA production in women can be caused by spermatozoal deposition in the genital tract, the peritoneal cavity, or the gastrointestinal tract with a compromised epithelial barrier . ASAs are estimated to cause infertility in 2-30% of infertile couples .
Previously, researchers have tried to use these antibodies and related antigens to create a contraceptive vaccine (CV) . They induced murine B cells to produce ASA by vaccinating them with the related antigen. The results demonstrated that vaccination with a sperm antigen or its cDNA can cause a long-term, reversible contraception in female mice. When the antibody titers declined to control levels, all the animals conceived and delivered healthy babies .
This study sparked our interest that ASAs could be very effective for a long-term and reversible contraception. As such, one of the aims of our project was to engineer L. jensenii to produce ASAs against a spermatozoa antigen.
Why do we chose to synthesize ASA ?
What is an antibody ?
The classical representation of an antibody is as a Y-shaped molecule composed of four polypeptide subunits with two identical heavy and light chains, linked by disulfur bonds. Each chain is composed of a constant part (constant heavy CH, constant light CL) and a variable part (variable heavy VH, variable light VL). It is secreted by B lymphocytes to specifically recognize and neutralize antigens.
Single-Chain Variable Fragments (scFv) are recombinant molecules where the variable region of the heavy (VH) and light (VL) immunoglobulin chains are linked into a single, flexible linker peptide sequence, here Gly4Ser. Glycine amino acids ensure a good flexibility of the linker. The effects of scFvs can be similar to antibodies, but they lack the complex assembly process of traditional antibodies and are thus easier to produce in prokaryotes.
ASA are immunoglobulins (IgG, IgA, IgM) directed against sperm antigens. The production can be caused whenever sperm encounters the immune system. They can have different effects.
Effects of ASAs on sperm
ASAs can affect fertility through inhibition of several mechanisms: sperm motility, capacitation, acrosome reaction, sperm-zona interaction, sperm-oolemma binding and penetration, and preimplantation embryonic development. The main activity of commercial spermicides is the inhibition of sperm motility, as if spermatozoa have their motility inhibited, they can no longer fertilize the egg . With this in mind, we chose several ASAs that have this effect.
Previous work on Lactobacillus jensenii:
An article by OSEL, a biotechnology company, discussed the production of scFvs against the HIV-1 virus by Lactobacillus jensenii. We studied their research in order to better understand their experiments and constructions. OSEL defined different promoters, such as RpsU and PtsU, that are specific to L. jensenii .
They determined a signal peptide that is specific to L. jensenii and added a linker to secrete a scFv antibody that targets HIV-1 .
Drawing inspiration from these studies, we modeled our system such that L. jensenii secretes our ASAs in a similar manner.
YLP20 and YLP12
After conducting a literature search of known ASAs, we found four interesting potential antibodies and related antigens. Of these, we decided to focus our research on YLP20, which was the most documented of the ASAs, and its antigen, YLP12. Additionally, YLP12 is a small peptide for which synthesis can easily be outsourced to test the potential activity of our antibody.
|AS16||Human Sperm Extract (HSE)|
The YLP20 scFv that we want to produce is composed of a heavy chain (VH), a light chain (VL), a linker (Gly4Ser), and an E-Tag.
Role of each part:
- VH and VL: compose the antigen-binding domain
- Linker Gly4Ser: link VH and VL
- E-Tag: allow for purification of our scFv using anti-E-Tag antibody
It is a 224 amino-acids sequence (with 13 more amino-acids for the E-tag sequence, for a total of 237) :
The bold parts are the different CDR (Coding DNA Region). The underlined part is the E-tag sequence. In blue is the light chain. In green is the heavy chain. The linker is highlighted in yellow.
YLP12 is dodecamer, composed of 12 amino acids. It is a sperm specific protein. This peptide sequence is involved in recognition and binding to the human oocyte zona pellucida (ZP), ZP protein, ZP3. YLP12 is present on acrosome, midpiece and tail regions of sperm cells.
It is a 12 amino-acids sequence : YLPVGGLRRIGG.
YLP12 was synthesized by EZBiolab with biotinylated C-terminus part.
We decided to add a biotinylated C-terminus part to fix YLP12 to use it as a capture antigen in an ELISA test. The biotinylated part is supposed to interact with the streptavidin in ELISA plate which will prevent the peptide to lie down. It will facilitate the interaction between the scFv and the peptide.
We first want to engineer L. jensenii and B. subtilis to make them produce YLP20 scFv. For that, We used a strong promoter, RpsU, that is specific to L. jensenii .
The scFv is synthesized from the N-terminus domain to C-terminus domain. The E-Tag is added at the end of the synthesis, on the C-term.
We used the same construction in L. jensenii and B. subtilis to test the production and secretion of our product. We do not know if the promoter works in B. subtilis as it is specific to L. jensenii, but both are gram negative bacteria. Once the scFv is fully synthesized, it is supposed to looks like Figure 1 (see below).
The next step is to make L. jensenii and B. subtilis secrete YLP20 scFv in the supernatant using a signal peptide (SP).
|Signal Peptide||Origin||Amino acid sequences|
We chose 4 differents SP to perform the secretion of scFv :
- Epr, YncM, YjfA
The first that we chose is CbsA. This SP is used for secretion of antibodies in Lactobacillus jensenii .
The SP is synthesized on the N-terminus domain. Downstream the CbsA sequence are added 4 amino acids (APVT) at the N-terminus domain of the scFv. These 4 amino acids are similar to a native signal peptidase cleavage site of this protein. The addition of the APVT sequence shown to improve the secretion of a full-length protein in L. jensenii.
These SPs are coming from a screening of SPs of Bacillus subtilis. As they can be used to secrete proteins in B. subtilis which is a gram positive bacteria, we decided to try to use them to secrete our stuff in L. jensenii that is also a gram positive bacteria. We used the same template for the construction. These SPs are on the N-terminus domain, and followed by the APVT sequence on their N-terminus domain.
|||Rajesh K. Naz, Subhash C.Chauhan. (2001). Presence of antibodies to sperm YLP12 synthetic peptide in sera and seminal plasma of immunoinfertile men. Molecular Human Reproduction Vol.7 no.1 pp. 21–26.|
|||Rajesh K. Naz. (2014). Vaccine for human contraception targeting sperm Izumo protein and YLP12 dodecamer peptide. Protein Science 2014 Vol.23:857—868.|
|||A.S. Samuel and R.K. Naz. (2008). Isolation of human single chain variable fragment antibodies against specific sperm antigens for immunocontraceptive development. Human Reproduction Vol.23, No.6 pp. 1324–1337.|
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