Methanobactins: Structures, Biosynthesis, and Microbial Diversity.

Methanobactins (Mbns) are ribosomally synthesized and posttranslationally modified peptide natural products released by methanotrophic bacteria under conditions of copper scarcity. Mbns bind Cu(I) with high affinity via nitrogen-containing heterocycles and thioamide groups installed on a precursor peptide, MbnA, by a core biosynthetic enzyme complex, MbnBC. Additional stabilizing modifications are enacted by other, less universal biosynthetic enzymes. Copper-loaded Mbn is imported into the cell by TonB-dependent transporters called MbnTs, and copper is mobilized by an unknown mechanism. The machinery to biosynthesize and transport Mbn is encoded in operons that are also found in the genomes of nonmethanotrophic bacteria. In this review, we provide an update on the state of the Mbn field, highlighting recent discoveries regarding Mbn structure, biosynthesis, and handling as well as the emerging roles of Mbns in the environment and their potential use as therapeutics.