Abstract
Abstract
Background: Transporter proteins are one of an organism’s primary interfaces with the environment. The
expressed set of transporters mediates cellular metabolic capabilities and influences signal transduction pathways
and regulatory networks. The functional annotation of most transporters is currently limited to general classification
into families. The development of capabilities to map ligands with specific transporters would improve our
knowledge of the function of these proteins, improve the annotation of related genomes, and facilitate predictions
for their role in cellular responses to environmental changes.
Results: To improve the utility of the functional annotation for ABC transporters, we expressed and purified the set
of solute binding proteins from Rhodopseudomonas palustris and characterized their ligand-binding specificity. Our
approach utilized ligand libraries consisting of environmental and cellular metabolic compounds, and fluorescence
thermal shift based high throughput ligand binding screens. This process resulted in the identification of specific
binding ligands for approximately 64% of the purified and screened proteins. The collection of binding ligands is
representative of common functionalities associated with many bacterial organisms as well as specific capabilities
linked to the ecological niche occupied by R. palustris.
Conclusion: The functional screen identified specific ligands that bound to ABC transporter periplasmic binding
subunits from R. palustris. These assignments provide unique insight for the metabolic capabilities of this organism
and are consistent with the ecological niche of strain isolation. This functional insight can be used to improve the
annotation of related organisms and provides a route to evaluate the evolution of this important and diverse
group of transporter proteins.