title: Effects of optional structural elements, including two alternative amino termini and a new splicing cassette IV, on the function of the sodium-bicarbonate cotransporter NBCn1 (SLC4A7).
abstract: The SLC4A7 gene encodes the electroneutral sodium/HCO3 cotransporter NBCn1, which plays important physiological and pathophysiological roles in many cell types. Previous work identified six NBCn1 variants differing in the sequence of the extreme N terminus--MEAD in rat only, MERF in human only--as well as in the optional inclusion of cassettes I, II, and III. Earlier work also left open the question of whether optional structural elements (OSEs) affect surface abundance or intrinsic (per-molecule) transport activity. Here, we demonstrate for the first time that SLC4A7 from one species can express both MEAD- and MERF-NBCn1. We also identify a novel cassette IV of 20 aa, and extend by 10 the number of full-length NBCn1 variants. The alternative N termini and four cassettes could theoretically produce 32 major variants. Moreover, we identify a group of cDNAs predicted to encode just the cytosolic N-terminal domain (Nt) of NBCn1. A combination of electrophysiology and biotinylation shows that the OSEs can affect surface abundance and intrinsic HCO3(-) transport activity of NBCn1, as expressed in Xenopus oocytes. Specifically, MEAD tends to increase whereas novel cassette IV reduces surface abundance. Cassettes II, III and novel cassette IV all appear to increase the intrinsic activity of NBCn1.
authors: L.-M. Chen: Department of Biophysics and Molecular Physiology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science and Technology, 1037 Luoyu Rd, Wuhan, Hubei, China 430074. liming.chen@mail.hust.edu.cn.
authors: Ying
authors: Y
authors: Liu
authors: Xue
authors: X
authors: Qin
authors: Deng-Ke
authors: DK
authors: Wang
authors: Yi-Min
authors: YM
authors: Guo
authors: Harindarpal S
authors: HS
authors: Gill
authors: Nathan
authors: N
authors: Morris
authors: Mark D
authors: MD
authors: Parker
authors: Li-Ming
authors: LM
authors: Chen
authors: Walter F
authors: WF
authors: Boron
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D051379:Mice; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D027982:Sodium-Bicarbonate Symporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014981:Xenopus
chemical_list: C422022:SLC4A7 protein, human; C498904:Slc4a7 protein, mouse; D027982:Sodium-Bicarbonate Symporters
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