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News & Blogs » Synthetic Biology News » Endogenous studies of SERINC5, a transmembrane protein critical for restricting HIV-1 infection, finally possible

Endogenous Studies of SERINC5, A Transmembrane Protein Critical for Restricting HIV-1 Infection, Finally Possible

Sep 26, 2020

CryoEM structure of SERINC from Drosophila melanogaster (PDB ID: 6PS2)

SERINC5 is a member of the serine incorporator family and is a transmembrane protein known to restrict HIV-1 infection. Studies have shown that its longest isoform, SERINC5.1, is incorporated into virion particles and possesses significant HIV-1 restriction activity. Furthermore, in cells overexpressing SERINC5.1 or cells infected with HIV-1 lacking a functional nef gene, SERINC5.1 has also been shown to render the virus more sensitive to neutralization by specific glycoprotein 41 neutralizing antibodies.

Despite being an important target for HIV-1 research, studies of SERINC5 function and activity have been largely limited to exogenously-expressed, tagged versions of the protein. Transmembrane proteins like SERINC5 which is composed of 10 transmembrane helices, are notoriously difficult targets for monoclonal antibody (mAb) generation due the complexity of their protein structure and limited availability of immunogenic epitopes to facilitate antigen recognition by the host’s immune system. As a result, the dearth of high-quality SERINC5-specific mAbs available have greatly limited immunoassay development to facilitate the detection and functional characterization of this protein.

Recently, however, a team of scientists at Walter Reed Army Institute of Research took major steps to overcome this obstacle by generating four specific SERINC5.1 mAbs. These mAbs were produced by targeting distinct epitopes from intracellular and extracellular loop regions on SERINC5.1 via a DNA-prime/peptide boost immunization approach using GenScript’s Antibody Services. Researchers then validated SERINC5.1 antibody specificity in an array of research applications such as Western blot and flow cytometry. Through immunocytochemistry staining of HEK293_S5.1 cells, a SERINC5.1 overexpressing cell line, with these mAbs, they were able to detect endogenous localization of SERINC5.1 at both the cell surface and within the cells. The researchers were additionally able to infer that SERINC5.1 orientation may differ from its native physiologic state in lymphocyte cells where there is lower epitope exposure, compared to adherent, overexpressing HEK293 cells. Scientists were also able to show that these mAbs will be extremely useful for virion studies because they bound specifically to their respective external/internal loops on HIV-1; 14C1-1 and 23E4-1 bound to surface exposed viral SERINC5, while 28E8-2 bound an internal loop.

These SERINC5.1 mAbs are valuable research reagents that open the door to facilitate studies of endogenous SERINC5 mechanisms not just in HIV-1 restriction, but also in the role the protein plays in cancer and neuroscience, and could even serve as lead mAbs for eventual therapeutic development.

Reference

1. Molnar, S. et al. Novel monoclonal antibodies to the SERINC5 HIV-1 restriction factor detect endogenous and virion-associated SERINC5. MAbs (2020). doi:10.1080/19420862.2020.1802187.
2. Cryo-EM structure of SERINC (PDB ID: 6PS2)
Pye, V. E. et al. A bipartite structural organization defines the SERINC family of HIV-1 restriction factors. Nat. Struct. Mol. Biol. (2020). doi:10.1038/s41594-019-0357-0.
3. Sehnal, D., Rose, A., Koča, J., Burley, S. & Velankar, S. Mol*: towards a common library and tools for web molecular graphics. Proc. Work. Mol. Graph. Vis. Anal. Mol. data (2018). doi:10.2312/molva.20181103, and RCSB PDB.