Spontaneity in the patellamide biosynthetic pathway.

Post-translationally modified ribosomal peptides are unusual natural products and many have potent biological activity. The biosynthetic processes involved in their formation have been delineated for some, but the patellamides represent a unique group of these metabolites with a combination of a macrocycle, small heterocycles and d-stereocentres. The genes encoding for the patellamides show very low homology to known biosynthetic genes and there appear to be no explicit genes for the macrocyclisation and epimerisation steps. Using a combination of literature data and large-scale molecular dynamics calculations with explicit solvent, we propose that the macrocyclisation and epimerisation steps are spontaneous and interdependent and a feature of the structure of the linear peptide. Our study suggests the steps in the biosynthetic route are heterocyclisation, macrocyclisation, followed by epimerisation and finally dehydrogenation. This study is presented as testable hypothesis based on literature and theoretical data to be verified by future detailed experimental investigations.