Structural Mechanism of the Active Bicarbonate Transporter from Cyanobacteria

Overview

Journal Nat Plants

Specialties Biology
Genetics

Date 2019 Nov 13

PMID 31712753

Citations 38

Authors

Chengcheng Wang

Bo Sun

Xue Zhang

Xiaowei Huang

Minhua Zhang

Hui Guo

Xin Chen

Fang Huang

Taiyu Chen

Hualing Mi

Fang Yu

Lu-Ning Liu

Peng Zhang

Affiliations

Soon will be listed here.

Abstract

Bicarbonate transporters play essential roles in pH homeostasis in mammals and photosynthesis in aquatic photoautotrophs. A number of bicarbonate transporters have been characterized, among which is BicA-a low-affinity, high-flux SLC26-family bicarbonate transporter involved in cyanobacterial CO-concentrating mechanisms (CCMs) that accumulate CO and improve photosynthetic carbon fixation. Here, we report the three-dimensional structure of BicA from Synechocystis sp. PCC6803. Crystal structures of the transmembrane domain (BicA) and the cytoplasmic STAS domain (BicA) of BicA were solved. BicA was captured in an inward-facing HCO-bound conformation and adopts a '7+7' fold monomer. HCO binds to a cytoplasm-facing hydrophilic pocket within the membrane. BicA is assembled as a compact homodimer structure and is required for the dimerization of BicA. The dimeric structure of BicA was further analysed using cryo-electron microscopy and physiological analysis of the full-length BicA, and may represent the physiological unit of SLC26-family transporters. Comparing the BicA structure with the outward-facing transmembrane domain structures of other bicarbonate transporters suggests an elevator transport mechanism that is applicable to the SLC26/4 family of sodium-dependent bicarbonate transporters. This study advances our knowledge of the structures and functions of cyanobacterial bicarbonate transporters, and will inform strategies for bioengineering functional BicA in heterologous organisms to increase assimilation of CO.

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