4M8J

Crystal structure of CaiT R262E bound to gamma-butyrobetaine

4M8J の概要

• エントリーDOI: 10.2210/pdb4m8j/pdb
• 分子名称: L-carnitine/gamma-butyrobetaine antiporter, 3-CARBOXY-N,N,N-TRIMETHYLPROPAN-1-AMINIUM (3 entities in total)
• 機能のキーワード: cait, leut fold, carnitine/gamma-butyrobetaine antiporter, plasma membrane, transport protein
• 由来する生物種: Proteus mirabilis
• 細胞内の位置: Cell membrane; Multi-pass membrane protein (By similarity): C2LLR0
• タンパク質・核酸の鎖数: 1
• 化学式量合計: 56431.49

構造登録者

Kalayil, S. (登録日: 2013-08-13, 公開日: 2013-10-09, 最終更新日: 2023-09-20)

主引用文献

Kalayil, S.,Schulze, S.,Kuhlbrandt, W.
Arginine oscillation explains Na+ independence in the substrate/product antiporter CaiT.
Proc.Natl.Acad.Sci.USA, 110:17296-17301, 2013

PubMed Abstract: Most secondary-active transporters transport their substrates using an electrochemical ion gradient. In contrast, the carnitine transporter (CaiT) is an ion-independent, l-carnitine/γ-butyrobetaine antiporter belonging to the betaine/carnitine/choline transporter family of secondary transporters. Recently determined crystal structures of CaiT from Escherichia coli and Proteus mirabilis revealed an inverted five-transmembrane-helix repeat similar to that in the amino acid/Na(+) symporter LeuT. The ion independence of CaiT makes it unique in this family. Here we show that mutations of arginine 262 (R262) make CaiT Na(+)-dependent. The transport activity of R262 mutants increased by 30-40% in the presence of a membrane potential, indicating substrate/Na(+) cotransport. Structural and biochemical characterization revealed that R262 plays a crucial role in substrate binding by stabilizing the partly unwound TM1' helix. Modeling CaiT from P. mirabilis in the outward-open and closed states on the corresponding structures of the related symporter BetP reveals alternating orientations of the buried R262 sidechain, which mimic sodium binding and unbinding in the Na(+)-coupled substrate symporters. We propose that a similar mechanism is operative in other Na(+)/H(+)-independent transporters, in which a positively charged amino acid replaces the cotransported cation. The oscillation of the R262 sidechain in CaiT indicates how a positive charge triggers the change between outward-open and inward-open conformations as a unifying critical step in LeuT-type transporters.

PubMed: 24101465
DOI: 10.1073/pnas.1309071110

実験手法

X-RAY DIFFRACTION (3.294 Å)