PDBsum entry 7a5c

Transport protein

PDB id: 7a5c

Contents

Protein chains

316 a.a.

Ligands

GOL ×2

Waters ×227

PDB id:

7a5c

Name:

Transport protein

Title:

Crystal structure of spin labelled vcsiap r125a bound to an artificial peptide ligand.

Structure:

Sialic acid-binding periplasmic protein siap. Chain: a, b. Engineered: yes. Mutation: yes

Source:

Vibrio cholerae serotype o1 (strain atcc 39315 / el tor inaba n16961). Organism_taxid: 243277. Strain: atcc 39315 / el tor inaba n16961. Gene: siap, vc_1779. Expressed in: escherichia coli. Expression_system_taxid: 562

Resolution:

2.20Å R-factor: 0.190 R-free: 0.234

Authors:

M.F.Peter,J.Glaenzer,G.Hagelueken

Key ref:

M.F.Peter et al. (2020). Triggering Closure of a Sialic Acid TRAP Transporter Substrate Binding Protein through Binding of Natural or Artificial Substrates. J Mol Biol, 433, 166756. PubMed id: 33316271 DOI: 10.1016/j.jmb.2020.166756

Date:

21-Aug-20 Release date: 30-Dec-20

Protein chains

Q9KR64  (SIAP_VIBCH) -  Sialic acid-binding periplasmic protein SiaP from Vibrio cholerae serotype O1 (strain ATCC 39315 / El Tor Inaba N16961)

Seq: 321 a.a.

Struc: 316 a.a.*

* PDB and UniProt seqs differ at 19 residue positions (black crosses)

Enzyme reactions

• Enzyme class: E.C.?

DOI no: 10.1016/j.jmb.2020.166756

J Mol Biol 433:166756 (2020)

PubMed id: 33316271

Triggering Closure of a Sialic Acid TRAP Transporter Substrate Binding Protein through Binding of Natural or Artificial Substrates.

M.F.Peter, C.Gebhardt, J.Glaenzer, N.Schneberger, M.de Boer, G.H.Thomas, T.Cordes, G.Hagelueken.

ABSTRACT

The pathogens Vibrio cholerae and Haemophilus influenzae use tripartite ATP-independent periplasmic transporters (TRAPs) to scavenge sialic acid from host tissues. They use it as a nutrient or to evade the innate immune system by sialylating surface lipopolysaccharides. An essential component of TRAP transporters is a periplasmic substrate binding protein (SBP). Without substrate, the SBP has been proposed to rest in an open-state, which is not recognised by the transporter. Substrate binding induces a conformational change of the SBP and it is thought that this closed state is recognised by the transporter, triggering substrate translocation. Here we use real time single molecule FRET experiments and crystallography to investigate the open- to closed-state transition of VcSiaP, the SBP of the sialic acid TRAP transporter from V. cholerae. We show that the conformational switching of VcSiaP is strictly substrate induced, confirming an important aspect of the proposed transport mechanism. Two new crystal structures of VcSiaP provide insights into the closing mechanism. While the first structure contains the natural ligand, sialic acid, the second structure contains an artificial peptide in the sialic acid binding site. Together, the two structures suggest that the ligand itself stabilises the closed state and that SBP closure is triggered by physically bridging the gap between the two lobes of the SBP. Finally, we demonstrate that the affinity for the artificial peptide substrate can be substantially increased by varying its amino acid sequence and by this, serve as a starting point for the development of peptide-based inhibitors of TRAP transporters.