Secondary structure of the membrane-bound domains of H+,K+-ATPase and Ca2+-ATPase, a comparison by FTIR after proteolysis treatment of the native membranes.
The sarcoplasmic reticulum Ca2+-ATPase and the gastric H+,K+-ATPase were cleaved under three different proteolysis conditions. After elimination of the protease and of the cleaved peptides, the vesicles containing the membrane-bound peptides of the ATPases were studied by Fourier transform attenuated total reflection infrared spectroscopy. In the harsher proteolysis conditions, the membrane-associated domain of the Ca2+-ATPase represented about 20% of the protein and was mainly constituted of alpha-helices. Polarized infrared spectroscopy showed that these alpha-helices were mainly oriented perpendicular to the membrane. However, only 10-20% of the H+,K+-ATPase was cleaved. The remaining, membrane-associated domain of the protein contained about 30% of alpha-helices and 30% of beta-sheet structures. The alpha-helices adopted a mainly transmembrane orientation. While the data on the Ca2+-ATPase are in general agreement with the current model of the protein, our results indicate that caution must be used in choosing this protein as a general structural model for all P-type ATPases. The protease-resistant, membrane-associated domain of the H+K+-ATPase is indeed much larger than predicted and also contained beta-sheet structures.
Raussens
V
V
Laboratoire de Chimie-Physique des Macromolécules aux Interfaces, Université Libre de Bruxelles, Brussels, Belgium.
le Maire
M
M
Ruysschaert
J M
JM
Goormaghtigh
E
E
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000737:chemistry* / Q000378:metabolism; D017506:H(+)-K(+)-Exchanging ATPase / Q000737:chemistry* / Q000378:metabolism; D006868:Hydrolysis; D007425:Intracellular Membranes / Q000201:enzymology*; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000737:chemistry / Q000201:enzymology; D017550:Spectroscopy, Fourier Transform Infrared; D013552:Swine
D008565:Membrane Proteins; D000255:Adenosine Triphosphate; D010447:Peptide Hydrolases; D017506:H(+)-K(+)-Exchanging ATPase; D000252:Calcium-Transporting ATPases