A complex lipoate utilization pathway in Listeria monocytogenes.

Although a complete pathway of lipoic acid metabolism has been established in Escherichia coli, lipoic acid metabolism in other bacteria is more complex and incompletely understood. Listeria monocytogenes has been shown to utilize two lipoate-protein ligases for lipoic acid scavenging, whereas only one of the ligases can function in utilization of host-derived lipoic acid-modified peptides. We report that lipoic acid scavenging requires not only ligation of lipoic acid but also a lipoyl relay pathway in which an amidotransferase transfers lipoyl groups to the enzyme complexes that require the cofactor for activity. In addition, we provide evidence for a new lipoamidase activity that could allow utilization of lipoyl peptides by lipoate-protein ligase. These data support a model of an expanded, three-enzyme pathway for lipoic acid scavenging that seems widespread in the Firmicutes phylum of bacteria.