Arg-Thz is a minimal substrate for the N(α),N(α)-arginyl methyltransferase involved in the biosynthesis of plantazolicin.

The final biosynthetic step towards plantazolicin (PZN) comprises N(α),N(α)-arginyl methyltransferase (PznL) mediated N-terminal bismethylation. We show that PznL processes truncated desmethyl-plantazolicin analogues, but only those with an N-terminal guanidine side chain derived from arginine. PznL specificity, which is narrow, depends on the side chain of the N-terminal amino acid linked to an azole, and not so much on the number of azoles.