2nd April 2019

Background:

Post Translational Modifications (PTM) are biochemical variations of cetain amino acids made to a protein after biosynthesis. These modifications diversify the proteome and play a fundamental role in regulation and targeting of proteins, their interactions with other molecules, as well as their structure, activity and function. Common types of post-translational modifications include phosphorylation, glycosylation, lipidation and carbonylation.

Citrullination involves the conversion of arginine in a protein into citrulline. In this reaction one of the terminal nitrogen atoms of the arginine side chain is replaced by an oxygen. Thus, arginine’s positive charge at physiological pH is removed, altering the protein’s charge distribution and tertiary structure. These modified proteins can be recognised and ‘attacked’ by the immune system, leading to autoimmune diseases such as rheumatoid arthritis and multiple sclerosis.

Figure 1: Arginine on the left (red) is citrullinated on the right (blue) by replacing the primary ketimine group (=NH) by a ketone group (=O ).

Example Data:

A customer approached us with two peptides (ten (10) amino acids in length) and asked that we generate aptamers which discriminate between the pre and post modified forms. Aptamer Group was able to enrich for aptamers to these peptides that showed population binding discrimination between the two peptides by Biolayer Interferometry (BLI).

Figure 2: The BioLayer Interferometry assay shows that the naïve population (green) does not bind to the target; the aptamer population shows strong binding to the non-modified Arginine containing peptide selection target (red), and weak binding to the citrullinated counter target (blue).

Conclusion:

Aptamer Group was able to generate a pool of aptamers that can discriminate between modified and non modified peptides. Due to the importance of PTMs in basic biology, as well as in disease pathogenesis, there is a significant interest in studying them by cell or tissue localization studies; purifying them individually or in complexes, and other proteomic analyses. The small structural differences make it difficult for typical antibody reagents to discriminate. Aptamers can provide a faster and simpler alternative.

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