8.A.91.  The TRAP Transporter TatT Protein Component (TatT) family

The bacterial acquisition of metabolites is largely facilitated by transporters with unique substrate scopes. The tripartite ATP-independent periplasmic (TRAP) transporters (TC# 2.A.56) comprise a large family of bacterial proteins that facilitate the uptake of a variety of small molecules. It has been reported that some TRAP systems encode a fourth protein, the T component, TatT). TatT is predicted to be a periplasmic-facing lipoprotein that enables the uptake of metabolites from the outer membrane. However, no substrates were previously revealed for any TatT, and their functional role(s) remained enigmatic. Zhai et al. 2023 identified a homolog in Methylococcus capsulatus that binds to sterols, and they reported two additional homologs that bind long-chain fatty acids. Their bioinformatics, quantitative analyses of protein-ligand interactions, and high-resolution crystal structures suggested that TatTs might facilitate the trafficking of hydrophobic or lipophilic substrates and thereby represent a new class of bacterial lipid and fatty acid transporters (Zhai et al. 2023). This hypothesis must remain speculative.



Zhai, L., J.C. Chou, H. Oo, and L. Dassama. (2023). Structures and mechanisms of a novel bacterial transport system for fatty acids. Chembiochem e202300156. [Epub: Ahead of Print]


TC#NameOrganismal TypeExample

TatT, a potentially novel bacterial transport system for fatty acids and other hydrophobic substrances. It may be an auxillary subunit of one or more TRAP-T system(s). See family  description for details.

TatT of Methylococcus capsulatus


Uncharacterized protein of 276 aas with one N-terminal TMS.

UP of Planctomycetota bacterium


Uncharacterized protein of 259 aas and one N-terminal TMS.

UP of Nitrospinota bacterium


Uncharacterized protein of 258 aas and 1 N-terminal TMS.

UP of Flavobacteriales bacterium (hot springs metagenome)


Uncharacterized protein of 292 aas and 1 N-terminal TMS.

UP of bacterium (freshwater metagenome)