Arginine methylation is a prevalent post‐translational modification in eukaryotic cells. Two significant debates exist within the field: do these enzymes dimethylate their substrates in a processive or distributive manner, and do these enzymes operate using a random or sequential method of bisubstrate binding? We revealed that human protein arginine N‐methyltransferase 1 (PRMT1) enzyme kinetics are dependent on substrate sequence. Further, peptides containing an Nη‐hydroxyarginine generally demonstrated substrate inhibition and had improved KM values, which evoked a possible role in inhibitor design. We also revealed that the perceived degree of enzyme processivity is a function of both cofactor and enzyme concentration, suggesting that previous conclusions about PRMT sequential methyl transfer mechanisms require reassessment. Finally, we demonstrated a sequential ordered Bi–Bi kinetic mechanism for PRMT1, based on steady‐state kinetic analysis. Together, our data indicate a PRMT1 mechanism of action and processivity that might also extend to other functionally and structurally conserved PRMTs.

License: Article 25fa pilot End User AgreementThis publication is distributed under the terms of Article 25fa of the Dutch Copyright Act (Auteurswet) with explicit consent by the author. Dutch law entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work.This publication is distributed under The Association of Universities in the Netherlands (VSNU) 'Article 25fa implementation' pilot project. In this pilot research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication.You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited.If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website.

The cover feature picture shows the cofactor SAM (teal) and the peptide binding groove (pink) within a PRMT1 dimer. We find that PRMT1 binds its substrates by using a sequential ordered mechanism in which binding of the cofactor SAM precedes binding of the target peptide similar to how putting on socks precedes putting on shoes—a handy metaphor. More information can be found in the full paper by N. I. Martin, A. Frankel et al. on page 85 in Issue 1, 2018 (DOI: 10.1002/cbic.201700521).