Extended Data Fig. 3: Investigation of the promiscuity in SN243 and its context.

(a) There is substantial evidence that GHs can have side activities in addition to the one that is considered their main activity of biological relevance. Catalytic promiscuity is difficult or impossible to predict, so collecting experimental evidence for promiscuity is crucial to gain a more systematic understanding of its occurrence. Some of the promiscuous activities of SN243 had been observed for β-glucuronidases before, but there is no previous report of an enzyme that was active on all these six glycosides. The thicker arrow highlights the new combination of a β-glucuronidase with promiscuous α-arabinofuranosidase activity added with the discovery of SN243. The figure tries to summarize the literature evidence by showing arrows staring at the main activity of an enzyme and pointing to the observed promiscuous activity. (Supplementary Fig. 17 gives the literature references in a replica of this plot indicated for each arrow in square brackets.) (b) Catalytic efficiencies (k_cat/K_M – left y-axis) for SN243 main and promiscuous activities vary between 10⁶ M⁻¹s⁻¹ (pNP-β-GlcA) and 10⁻¹ M⁻¹s⁻¹ (pNP-α-L-Araf), which corresponds to second order rate enhancements (right y-axis) in the range of 10¹⁴ and 10⁷, respectively. Detailed kinetic information can be found in Table 1 and Supplementary Table 6.