Norwegian Centre for Molecular Medicine, Nordic EMBL Partnership University of Oslo, Gaustadalléen 21, 0349, Oslo, Norway.
Department of Biomedicine, Aarhus University, 8000, Aarhus, Denmark.
Sci Rep. 2017 Sep 21;7(1):12131. doi: 10.1038/s41598-017-12409-0.
The sodium-driven chloride/bicarbonate exchanger (NDCBE) is essential for maintaining homeostatic pH in neurons. The crystal structure at 2.8 Å resolution of the regulatory N-terminal domain of human NDCBE represents the first crystal structure of an electroneutral sodium-bicarbonate cotransporter. The crystal structure forms an equivalent dimeric interface as observed for the cytoplasmic domain of Band 3, and thus establishes that the consensus motif VTVLP is the key minimal dimerization motif. The VTVLP motif is highly conserved and likely to be the physiologically relevant interface for all other members of the SLC4 family. A novel conserved Zn-binding motif present in the N-terminal domain of NDCBE is identified and characterized in vitro. Cellular studies confirm the Zn dependent transport of two electroneutral bicarbonate transporters, NCBE and NBCn1. The Zn site is mapped to a cluster of histidines close to the conserved ETARWLKFEE motif and likely plays a role in the regulation of this important motif. The combined structural and bioinformatics analysis provides a model that predicts with additional confidence the physiologically relevant interface between the cytoplasmic domain and the transmembrane domain.
钠驱动的氯离子/碳酸氢根交换器（NDCBE）对于维持神经元内的酸碱稳态至关重要。人类 NDCBE 调节 N 端结构域的 2.8Å 分辨率晶体结构代表了第一个电中性钠离子-碳酸氢根共转运蛋白的晶体结构。晶体结构形成了与细胞质域的 Band 3 观察到的相同的二聚体界面，因此确立了 VTVLP 基序是关键的最小二聚化基序。VTVLP 基序高度保守，可能是 SLC4 家族所有其他成员的生理相关界面。在 NDCBE 的 N 端结构域中鉴定并表征了一个新的保守 Zn 结合基序。细胞研究证实了两种电中性碳酸氢盐转运蛋白 NCBE 和 NBCn1 的 Zn 依赖性转运。Zn 位点被映射到靠近保守的 ETARWLKFEE 基序的一组组氨酸附近，可能在调节这个重要基序中发挥作用。综合结构和生物信息学分析提供了一个模型，该模型更有信心地预测了细胞质域和跨膜域之间的生理相关界面。
