Fuzziness endows viral motif-mimicry.

Motif-mimicry is exploited by viruses to interfere with host regulatory networks and has also been suggested as a prevalent strategy for eukaryotic and prokaryotic pathogens. Using the same peptide motif however does not guarantee more effective interactions with the host. Motif-mediated interactions require a flexible or disordered environment, with structural and dynamic features that should differ between the competing host and viral proteins. Using the eukaryotic linear motif (ELM) database we analyzed the protein regions which contained the eukaryotic and viral motifs, including human and human virus ELMs with common target sites. We found that although the eukaryotic motifs are associated with a lack of structure, they are more stable than their flanking regions and can serve as molecular recognition elements. In contrast, eukaryotic viral motifs are often located in more ordered regions, but have increased local flexibility or disorder compared to their embedding environment. Most viral ELMs are devoid of stable binding elements and remain fuzzy after binding. Fuzziness reduces the entropic cost of binding and imparts versatile interaction modes to increase binding promiscuity and to compete with multiple host peptides. Fuzzy interactions confer further functional benefits such as the combinatorial usage of motifs, and a fine-tuning affinity via post-translational modifications.