The roles of carbohydrate chains of the beta-subunit on the functional expression of gastric H(+),K(+)-ATPase.
Gastric H(+),K(+)-ATPase consists of alpha and beta-subunits. The alpha-subunit is the catalytic subunit, and the beta-subunit is a glycoprotein stabilizing the alpha/beta complex in the membrane as a functional enzyme. There are seven putative N-glycosylation sites on the beta-subunit. In this study, we examined the roles of the carbohydrate chains of the beta-subunit by expressing the alpha-subunit together with the beta-subunit in which one, several, or all of the asparagine residues in the N-glycosylation sites were replaced by glutamine. Removing any one of seven carbohydrate chains from the beta-subunit retained the H(+),K(+)-ATPase activity. The effects of a series of progressive removals of carbohydrate chains on the H(+),K(+)-ATPase activity were cumulative, and removal of all carbohydrate chains resulted in the complete loss of H(+), K(+)-ATPase activity. Removal of any single carbohydrate chain did not affect the alpha/beta assembly; however, little alpha/beta assembly was observed after removal of all the carbohydrate chains from the beta-subunit. In contrast, removal of three carbohydrate chains inhibited the surface delivery of the beta-subunit and the alpha-subunit assembled with the beta-subunit, indicating that the surface delivery mechanism is more dependent on the carbohydrate chains than the expression of the H(+),K(+)-ATPase activity and alpha/beta assembly.
Asano
S
S
Molecular Genetics Research Center, 2630 Sugitani, Toyama 930-0194, Japan. shinji@ms.toyama-mpu.ac.jp
Kawada
K
K
Kimura
T
T
Grishin
A V
AV
Caplan
M J
MJ
Takeguchi
N
N
D000818:Animals; D019556:COS Cells; D002451:Cell Compartmentation; D005753:Gastric Mucosa / Q000201:enzymology*; D015971:Gene Expression Regulation, Enzymologic; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D006031:Glycosylation; D017506:H(+)-K(+)-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism
D006023:Glycoproteins; D011994:Recombinant Proteins; D017506:H(+)-K(+)-Exchanging ATPase