Abstract
Tripartite ATP-independent periplasmic transporters (TRAP-Ts) are bacterial transport systems that have been implicated in the import of small molecules into the cytoplasm. A newly discovered subfamily of TRAP-Ts [tetratricopeptide repeat-protein associated TRAP transporters (TPATs)] has four components. Three are common to both TRAP-Ts and TPATs: the P component, a ligand-binding protein, and a transmembrane symporter apparatus comprising the M and Q components (M and Q are sometimes fused to form a single polypeptide). TPATs are distinguished from TRAP-Ts by the presence of a unique protein called the T component. In Treponema pallidum, this protein (TatT) is a water-soluble trimer whose protomers are each perforated by a pore. Its respective P component (TatP T) interacts with the TatT in vitro and in vivo. In this work, we further characterized this interaction. Co-crystal structures of two complexes between the two proteins confirm that up to three monomers of TatPT can bind to the TatT trimer. A putative ligand-binding cleft of TatPT aligns with the pore of TatT, strongly suggesting ligand transfer between T and PT. We used a combination of site-directed mutagenesis and analytical ultracentrifugation to derive thermodynamic parameters for the interactions. These observations confirm that the observed crystallographic interface is recapitulated in solution. These results prompt a hypothesis of the molecular mechanism(s) of hydrophobic ligand transport by the TPATs.
Original language | English (US) |
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Pages (from-to) | 70-86 |
Number of pages | 17 |
Journal | Journal of Molecular Biology |
Volume | 420 |
Issue number | 1-2 |
DOIs | |
State | Published - Jun 29 2012 |
Keywords
- TPR motif
- TRAP transporter
- Treponema pallidum
- protein interactions
- syphilis
ASJC Scopus subject areas
- Structural Biology
- Molecular Biology