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Deletions in the A(L) region of the h4xb plasma membrane Ca(2+) pump. High apparent affinity for Ca(2+) of a deletion mutant resembling the alternative spliced form h4zb
Authors:de Tezanos Pinto Felicitas  Adamo Hugo P
Institution:IQUIFIB-Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires Junín 956, 1113 Buenos Aires, Argentina.
Abstract:Mutants of the plasma membrane Ca(2+) pump (human isoform 4xb) with deletions in the linker between domain A and transmembrane segment M3 (A(L) region) were constructed and expressed in Chinese hamster ovary cells. The total or partial removal of the amino acid segment 300-349 did not change the maximal Ca(2+) transport activity, but mutants with deletions involving residues 300-338 exhibited a higher apparent affinity for Ca(2+) than the wild type h4xb enzyme. Deletion of the putative acidic lipid interacting sequence (residues 339-349) had no observable functional consequences. The removal of either residues 300-314 or 313-338 resulted in a similar increase in the apparent Ca(2+) affinity of the pump although the increase was somewhat lower than that obtained by the deletion 300-349 suggesting that both deletions affected the same structural determinant. The results show that alterations in the region of the alternative splicing site A change the sensitivity to Ca(2+) of the human isoform 4 of the PMCA.
Keywords:PMCA  plasma membrane Ca2+ pump  h4xb  x at the splicing site “A” and spliced form b at the splicing site “C”" target="_blank">plasma membrane Ca2+ pump derived from the human gene 4 spliced form x at the splicing site “A” and spliced form b at the splicing site “C”  h4zb  z at the splicing site “A” and spliced form b at the splicing site “C”" target="_blank">human PMCA isoform 4 spliced form z at the splicing site “A” and spliced form b at the splicing site “C”  ct120  h4xb lacking the C-terminal 120 amino acids  SERCA  sarcoplasmic/endoplasmic Ca2+ pump  M1-M10  putative transmembrane segments of the PMCA numbered from the N-terminal end of the peptide  CHO  Chinese hamster ovary  The deletions are indicated as d(n1-n2) where n1 and n2 indicate the first and the last amino acids that were deleted without taking in account the threonine and arginine residues introduced by the construction of the deletions
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