PDBsum entry 4jb2

Transport protein

PDB id: 4jb2

Contents

Protein chain

357 a.a.

Ligands

GOL ×4

Waters ×67

PDB id:

4jb2

Name:

Transport protein

Title:

Rhodopseudomonas palustris (strain cga009) rp1789

Structure:

Branched-chain amino acid transport system substrate- binding protein. Chain: a. Engineered: yes

Source:

Rhodopseudomonas palustris. Organism_taxid: 258594. Strain: atcc baa-98 / cga009. Gene: 1789. Expressed in: escherichia coli. Expression_system_taxid: 469008.

Resolution:

2.10Å R-factor: 0.177 R-free: 0.228

Authors:

R.Salmon

Key ref:

R.C.Salmon et al. (2013). The CouPSTU and TarPQM transporters in Rhodopseudomonas palustris: redundant, promiscuous uptake systems for lignin-derived aromatic substrates. Plos One, 8, e59844. PubMed id: 23555803 DOI: 10.1371/journal.pone.0059844

Date:

19-Feb-13 Release date: 17-Apr-13

Protein chain

Q6N8W4  (Q6N8W4_RHOPA) -  Branched-chain amino acid transport system substrate-binding protein from Rhodopseudomonas palustris (strain ATCC BAA-98 / CGA009)

Seq: 385 a.a.

Struc: 357 a.a.

Enzyme reactions

• Enzyme class: E.C.?

DOI no: 10.1371/journal.pone.0059844

Plos One 8:e59844 (2013)

PubMed id: 23555803

The CouPSTU and TarPQM transporters in Rhodopseudomonas palustris: redundant, promiscuous uptake systems for lignin-derived aromatic substrates.

R.C.Salmon, M.J.Cliff, J.B.Rafferty, D.J.Kelly.

ABSTRACT

The biodegradation of lignin, one of the most abundant carbon compounds on Earth, has important biotechnological applications in the derivation of useful products from lignocellulosic wastes. The purple photosynthetic bacterium Rhodopseudomonas palustris is able to grow photoheterotrophically under anaerobic conditions on a range of phenylpropeneoid lignin monomers, including coumarate, ferulate, caffeate, and cinnamate. RPA1789 (CouP) is the periplasmic binding-protein component of an ABC system (CouPSTU; RPA1789, RPA1791-1793), which has previously been implicated in the active transport of this class of aromatic substrate. Here, we show using both intrinsic tryptophan fluorescence and isothermal titration calorimetry that CouP binds a range of phenylpropeneoid ligands with K d values in the nanomolar range. The crystal structure of CouP with ferulate as the bound ligand shows H-bond interactions between the 4-OH group of the aromatic ring with His309 and Gln305. H-bonds are also made between the carboxyl group on the ferulate side chain and Arg197, Ser222, and Thr102. An additional transport system (TarPQM; RPA1782-1784), a member of the tripartite ATP-independent periplasmic (TRAP) transporter family, is encoded at the same locus as rpa1789 and several other genes involved in coumarate metabolism. We show that the periplasmic binding-protein of this system (TarP; RPA1782) also binds coumarate, ferulate, caffeate, and cinnamate with nanomolar K d values. Thus, we conclude that R. palustris uses two redundant but energetically distinct primary and secondary transporters that both employ high-affinity periplasmic binding-proteins to maximise the uptake of lignin-derived aromatic substrates from the environment. Our data provide a detailed thermodynamic and structural basis for understanding the interaction of lignin-derived aromatic substrates with proteins and will be of use in the further exploitation of the flexible metabolism of R. palustris for anaerobic aromatic biotransformations.