Having estimated the free energy landscapes for the capped amino acids, we now evaluate the activity for both ff99SB and ff03 (see Figure ). The first set of molecular dynamics corresponds to an hexapeptide with sequence Ace-XGPGXG-Nme, where X can be either mimosine, pheny-lalanine or tyrosine (see Methods). To characterize the dimensions of these peptides we estimate the distribution of the radius of gyration (R g , see Figure ). We find that the distributions differ significantly between the Mms hexapeptide and its analogues including Phe and Tyr. Specifically, the distributions of R g values of the mimosine peptide are narrower and are centered at higher radius values than those of the Phe/Tyr peptides, suggesting the prevalence of conformations with a more expanded chain for the Mms peptide. The maxima for both force fields in the case of the mimosine hexapeptide are at ⇠0.51 nm and the relative frequencies reached are considerably higher than those observed for either the Phe or Tyr peptides, with over 58% and 41% of the population being between 0.49 and 0.53 nm for ff99SB and ff03, respectively. While the distribution is slightly broader for ff03, the same trend can be observed for both force fields. This result suggests that geometries that are not particularly important for Phe/Tyr peptides, become much more favourable for the Mms peptide. Further inspection of the trajectories revealed that mimosine significantly favours conformations where the peptide rings can interact. This is captured by the maxima around 0.44 nm in the distribution of inter-ring distances, shown in Figure . The same trends can be observed for both force fields, although to a different degree, with the preference for short inter-ring distances being more prominent for ff99sb. Additionally, a second maximum in the population appears at distances around 0.84 nm, which dominates in the Phe/Tyr peptides, and is stabilized mainly by backbone interactions. Therefore, the hexapeptide presents two dominant conformations, one stabilized by interactions between the Mms rings and a second one stabilized by interactions in the backbone leaving its Mms rings at longer distances. On the other hand, the Phe and Tyr hexapeptides show only one prevalent conformation, the latter one. To understand the interactions between the Mms rings, we analysed their relative orientations. In Figure we show the distribution of the angle q between the rings, which is drastically different in the mimosine peptide from that in both the Phe and Tyr peptides.