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The cysteines in NBCe1‐A extracellular loop 3 form intra‐molecular disulfide bonds that determines the transporter surface topography
Author(s) -
Zhu Quansheng,
Kao Liyo,
Azimov Rustam,
Liu Weixin,
Newman Debra,
Kurtz Ira
Publication year - 2012
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.26.1_supplement.689.4
Subject(s) - chemistry , loop (graph theory) , transporter , disulfide bond , stereochemistry , glycosylation , biochemistry , gene , mathematics , combinatorics
A common feature among the Na + ‐dependent members of the SLC4 bicarbonate transporter family is the presence of four cysteines (Cys) in the glycosylated extracellular loop 3 (EC‐loop 3). We recently determined that EC‐loop 3 is the largest highly exposed surface loop in NBCe1‐A and resides at the dimer interface. In the present study, we extensively analyzed the pattern of disulfide bond formation among the four Cys in the NBCe1‐A EC‐loop 3 and discovered: 1) the four cys in EC‐loop 3 are in a folded conformation and intra‐disulfided; 2) cys 583/585 and cys 630/642 form two disulfide bonds; 3) the first disulfide bond (cys 583/585) determines the number of glycosylation sites in EC‐loop 3; 4) glycosylation of EC‐loop 3 guides the disulfide bond formation between cys 630 and 642; 5) in the absence of the four endogenous cys, NBCe1‐A traffics normally to the plasma membrane, however, unlike wild‐type NBCe1‐A, Asn 582 becomes glycosylated; furthermore, every introduced cys in EC‐loop 3 (Tyr 567 to Asp 647) becomes self cross‐linked. Our findings suggest that the EC‐loop 3 from each NBCe1‐A monomer interact to form a domain‐like structure on the surface of the dimerized transporter whose physiological function is currently unknown.