Topology and biosynthesis of the anion exchanger 1 mutant of Southeast Asian ovalocytosis.
Published: 2005
Language: eng
Number of pages: 217
Description: Anion exchanger 1 (AE1) is a palmitoylated membrane glycoprotein responsible for chloride/bicarbonate exchange in erythrocytes. An N-terminally truncated version (kAE1) is present at the basolateral membrane of kidney alpha-intercalated cells. Southeast Asian ovalocytosis (SAO) is caused by deletion of Ala400-Ala408 at the boundary of the cytosolic domain and transmembrane segment (TM) 1 of AE1, resulting in a protein that is misfolded and inactive in anion transport.These studies in AE1 and various mutants have revealed novel aspects in AE1 topology and biosynthesis, and have raised questions for further investigation. Future studies on this model protein will help us to better understand its structure, function, biosynthesis, and membrane proteins in general.A role of palmitoylation in AE1 biosynthesis was investigated using transfected cells. AE1 could traffic to the cell surface, although no palmitoylation was detected, suggesting that palmitoylation is not essential for surface expression of AE1. Further studies are required to determine the function of AE1 palmitoylation.Scanning N-glycosylation mapping of full-length proteins expressed in a cell-free system and transfected cells showed that membrane integration of SAO TM1 is impaired. However, its C-terminal end is positioned similarly to AE1 TM1 in the membrane, suggesting that residues N-terminal of the SAO deletion may be pulled into the membrane to compensate for the helical length of SAO TM1.Scanning N-glycosylation mapping of TM2-3 region in AE1 indicates exposure of the region to the endoplasmic reticulum lumen during biosynthesis, suggesting that it may form a re-entrant loop. A refinement of the lumenal ends of TMs 1 and 4 in the AE1 folding model is presented. In contrast to AE1, TM2-3 sites in AE1 SAO were not glycosylated. TMs 1 and 2 are likely exposed to the cytosol in most SAO proteins.The effect of SAO deletion on AE1 biosynthesis was examined in transfected HEK293 and polarized MDCK cells. Erythroid and kidney SAO proteins can form homodimers and heterodimers with normal proteins; presence of normal proteins could rescue SAO protein trafficking. Erythroid-specific mechanisms may also be involved in trafficking AE1 SAO in erythroid precursors.
Notes: Source: Dissertation Abstracts International, Volume: 66-10, Section: B, page: 5377.

Thesis (Ph.D.)--University of Toronto, 2005.

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