Crystal structure of the sugar acid‐binding protein CxaP from a TRAP transporter in Advenella mimigardefordensis strain DPN7^T

Abstract

Recently, CxaP, a sugar acid substrate binding protein (SBP) from Advenella mimigardefordensis strain DPN7 T was identified as part of a novel sugar uptake strategy. In the current study, the protein was successfully crystallized. Although several SBP structures of TRAP transporters have already been solved, this is the first structure of an SBP accepting multiple sugar acid ligands. Protein crystals were obtained with bound D-xylonic acid, D-fuconic acid Dgalactonic and D-gluconic acid, respectively. The protein shows the typical structure of an SBP of a TRAP transporter consisting of two domains linked by a hinge and spanned by a long α-helix. By analysis of the structure, the substrate binding site of the protein was identified. The carboxylic group of the sugar acids interacts with Arg175, whereas the coordination of the hydroxylic groups at positions C2 and C3 are most probably realized by Arg154 and Asn151. Furthermore, it was observed that 2-keto-3-deoxy-D-gluconic acid is bound in protein crystals which were crystallized without the addition of any ligand, indicating that this molecule is pre-bound to the protein and is displaced by the other ligands if they are available.

Structure, substrate selectivity determinants and membrane interactions of a Glutamate-specific TAXI TRAP binding protein fromVibrio cholerae

“…The vast majority of our understanding of TRAP transporter structure and function comes from the characterization of DctP-type TRAP transporters 4,[7][8][9][10][11][12][13][14][15][16][17][18][19][20] , most prominently, a sialic acid-specific member from Haemophilus influenzae, SiaPQM (HiSiaP is the SBP and HiSiaQM is the fused membrane component) 3,[20][21][22][23][24][25][26] . Work from multiple labs on a variety of TRAP SBPs has revealed that, like SBPs from ATP-binding cassette (ABC) transporters, they utilize a venus flytrap type mechanism, in which the binding of ligand to the open apo state triggers closure of the two α/β globular domains around the substrate 27 .…”