Sequon

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A sequon is a sequence of consecutive amino acids in a polypeptide that can serve as an attachment site for a polysaccharide , often an N -linked glycan . In this case, the glycan is bound to the protein via the nitrogen atom in the side chain of asparagine (Asn) . Sequons for N-glycosylation usually consist of three amino acids with the consensus sequence Asn-X-Ser or Asn-X-Thr, where X can be any amino acid except proline , Ser stands for serine and Thr stands for threonine . Occasionally, other amino acids can take the place of Ser and Thr, such as in the leukocyte surface protein CD69 , where the recognition sequence Asn-X-Cys is an acceptable sequence for the attachment of N -linked glycans.

However, a sequon is neither a necessary nor a sufficient condition for glycosylation. In some cases, glycans are attached to asparagine side chains that are not in a sequon. In secreted proteins, approximately one third of the Asn of sequons are not glycosylated.

In genetic engineering practice, artificial glycosylation sites, i.e. sequons, are often created in a polypeptide with the help of site-directed mutagenesis . By means of targeted insertions or exchanges in the base sequence of a coding nucleic acid, the coded amino acid sequence of the polypeptide can be modified in such a way that new effective sequons then appear or previously existing sequons become unrecognizable. In the subsequent post-translational processing , the newly added glycosylation sites are recognized or the disfigured attachment sites are ignored, so that the finished processed polypeptide product (protein) has a modified, artificially created glycosylation pattern. This can be useful, for example, in the design of potential antigens to generate a vaccine, such as a dengue virus vaccine against dengue virus or Zika virus .

Individual evidence

  1. ↑ Sequon - an overview | ScienceDirect Topics at www.sciencedirect.com; accessed May 21, 2019.
  2. ^ Susan Brooks: Functional and molecular glycobiology . BIOS Scientific, Oxford, UK 2002, ISBN 1-85996-022-7
  3. ^ Benjamin Schulz: Beyond the Sequon: Sites of N-Glycosylation. ( doi: 10.5772 / 50260 ) In: Stefana Petrescu (Ed.): Glycolysation. IntechOpen, 2012, ISBN 978-953-51-0771-2 , p. 22f.
  4. ↑ European patent EP3458471 from Excivion Ltd. 2018, paragraph 0025 of the online text , p. 9 line 2 in the original; accessed May 27, 2020.