title: Structural and thermodynamic characterization of the interaction between two periplasmic Treponema pallidum lipoproteins that are components of a TPR-protein-associated TRAP transporter (TPAT).
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 TatP(T) can bind to the TatT trimer. A putative ligand-binding cleft of TatP(T) aligns with the pore of TatT, strongly suggesting ligand transfer between T and P(T). 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.
authors.affiliation: Department of Biochemistry, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
authors.forename: Chad A
authors.initials: CA
authors.lastname: Brautigam
authors.forename: Ranjit K
authors.initials: RK
authors.lastname: Deka
authors.forename: Peter
authors.initials: P
authors.lastname: Schuck
authors.forename: Diana R
authors.initials: DR
authors.lastname: Tomchick
authors.forename: Michael V
authors.initials: MV
authors.lastname: Norgard
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008074:Lipoproteins / Q000737:chemistry*; D008958:Models, Molecular; D033902:Periplasmic Binding Proteins / Q000737:chemistry*; D033903:Periplasmic Proteins / Q000737:chemistry; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012996:Solutions; D013816:Thermodynamics; D014210:Treponema pallidum / Q000737:chemistry*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D008074:Lipoproteins; D033902:Periplasmic Binding Proteins; D033903:Periplasmic Proteins; D012996:Solutions; C406409:Tpr protein, Treponema