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PMID:10801856

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Citation

Mandal, D, Woolf, TB and Rao, R (2000) Manganese selectivity of pmr1, the yeast secretory pathway ion pump, is defined by residue gln783 in transmembrane segment 6. Residue Asp778 is essential for cation transport. J. Biol. Chem. 275:23933-8

Abstract

We have solubilized and purified the histidine-tagged yeast secretory pathway/Golgi ion pump Pmr1 to near homogeneity in one step, using nickel affinity chromatography. The purified pump demonstrates both Ca(2+)- and Mn(2+)-dependent ATP hydrolysis and phosphoenzyme intermediate formation in forward (ATP) and reverse (P(i)) directions. This preparation has allowed us to examine, in detail, the properties of mutations D778A and Q783A in transmembrane segment M6 of Pmr1. In phenotypic screens of Ca(2+) chelator and Mn(2+) toxicity reported separately (Wei, Y., Chen, J., Rosas, G., Tompkins, D.A., Holt, P.A., and Rao, R. (2000) J. Biol. Chem. 275, XXXX-XXXX), D778A was a loss-of-function mutant apparently defective for transport of both Ca(2+) and Mn(2+), whereas mutant Q783A displayed a differential sensitivity consistent with the selective loss of Mn(2+) transport. We show that mutant D778A is devoid of cation-dependent ATP hydrolytic activity and phosphoenzyme formation from ATP. However, reverse phosphorylation from P(i) is preserved but is insensitive to inhibition by Ca(2+) or Mn(2+) ions, which is evidence for a specific inability to bind cations in this mutant. We also show that Ca(2+) can activate ATP hydrolysis in the purified Q783A mutant, with a half-maximal concentration of 0.06 micrometer, essentially identical to that of wild type (0.07 micrometer). Mn(2+) activation of ATP hydrolysis was half-maximal at 0.02 micrometer in wild type, establishing a normal selectivity profile of Mn(2+) > Ca(2+). Strikingly, Mn(2+)-ATPase in the Q783A mutant was nearly abolished, even at concentrations of up to 10 micrometer. These results were confirmed in assays of phosphoenzyme intermediates. Molecular modeling of the packing between helices M4 and M6 suggests that residue Gln(783) in M6 may form a critical hydrophobic interaction with Val(335) in M4, such that the Ala substitution modifies the packing or tilt of the helices and thus the ion pore. The data emphasize the critical role of transmembrane segment M6 in defining the cation binding pocket of P-type ATPases.

Links

PubMed Online version:10.1074/jbc.M002619200

Keywords

ATP-Binding Cassette Transporters/genetics; ATP-Binding Cassette Transporters/isolation & purification; ATP-Binding Cassette Transporters/metabolism; Adenosine Triphosphatases/genetics; Adenosine Triphosphatases/isolation & purification; Adenosine Triphosphatases/metabolism; Adenosine Triphosphate/metabolism; Amino Acid Sequence; Aspartic Acid; Binding Sites; Calcium-Transporting ATPases/genetics; Cations, Divalent/metabolism; Egtazic Acid/analogs & derivatives; Egtazic Acid/metabolism; Fungal Proteins/secretion; Glutamine; Histidine; Ion Pumps/genetics; Ion Pumps/isolation & purification; Ion Pumps/metabolism; Manganese/metabolism; Models, Molecular; Molecular Sequence Data; Mutation; Peptides; Phosphoproteins/metabolism; Phosphorylation; Protein Structure, Secondary; Protein Structure, Tertiary; Saccharomyces cerevisiae Proteins; Sarcoplasmic Reticulum Calcium-Transporting ATPases

Significance

Annotations

Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status

YEAST:ATC1

involved_in

GO:0006828: manganese ion transport

ECO:0000314: direct assay evidence used in manual assertion

P

Seeded From UniProt

complete

YEAST:ATC1

enables

GO:0140613: P-type manganese transporter activity

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete


See also

References

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