7F6P

Crystal structure of metal-citrate-binding mutant (D28A) protein (MctA) of ABC transporter endogenously bound to citrate

Summary for 7F6P

• Entry DOI: 10.2210/pdb7f6p/pdb
• Descriptor: Iron ABC transporter, periplasmic iron-binding protein, CITRIC ACID, 1,2-ETHANEDIOL, ... (7 entities in total)
• Functional Keywords: substrate-binding protein, metal ion, secondary transporter, symporter, transport protein
• Biological source: Thermus thermophilus (strain ATCC 27634 / DSM 579 / HB8)
• Total number of polymer chains: 3
• Total formula weight: 115439.05

Authors

Kanaujia, S.P.,Mandal, S.K. (deposition date: 2021-06-25, release date: 2021-12-01, Last modification date: 2023-11-29)

Primary citation

Mandal, S.K.,Kanaujia, S.P.
Structural and thermodynamic insights into a novel Mg 2+ -citrate-binding protein from the ABC transporter superfamily.
Acta Crystallogr D Struct Biol, 77:1516-1534, 2021

PubMed Abstract: More than one third of proteins require metal ions to accomplish their functions, making them obligatory for the growth and survival of microorganisms in varying environmental niches. In prokaryotes, besides their involvement in various cellular and physiological processes, metal ions stimulate the uptake of citrate molecules. Citrate is a source of carbon and energy and is reported to be transported by secondary transporters. In Gram-positive bacteria, citrate molecules are transported in complex with divalent metal ions, whereas in Gram-negative bacteria they are translocated by Na/citrate symporters. In this study, the presence of a novel divalent-metal-ion-complexed citrate-uptake system that belongs to the primary active ABC transporter superfamily is reported. For uptake, the metal-ion-complexed citrate molecules are sequestered by substrate-binding proteins (SBPs) and transferred to transmembrane domains for their transport. This study reports crystal structures of an Mg-citrate-binding protein (MctA) from the Gram-negative thermophilic bacterium Thermus thermophilus HB8 in both apo and holo forms in the resolution range 1.63-2.50 Å. Despite binding various divalent metal ions, MctA possesses the coordination geometry to bind its physiological metal ion, Mg. The results also suggest an extended subclassification of cluster D SBPs, which are known to bind and transport divalent-metal-ion-complexed citrate molecules. Comparative assessment of the open and closed conformations of the wild-type and mutant MctA proteins suggests a gating mechanism of ligand entry following an `asymmetric domain movement' of the N-terminal domain for substrate binding.

PubMed: 34866608
DOI: 10.1107/S2059798321010457

Experimental method

X-RAY DIFFRACTION (2.15 Å)