cAMP-dependent protein kinase (A-kinase) anchoring proteins (AKAPs) ar
e responsible for the subcellular sequestration of the type II A-kinas
e. Previously, we identified a 78 kDa AKAP which was enriched in gastr
ic parietal cells. We have now purified the 78 kDa AKAP to homogeneity
from gastric fundic mucosal supernates using type II A-kinase regulat
ory subunit (R(II)) affinity chromatography. The purified 78 kDa AKAP
was recognized by monoclonal antibodies against ezrin, the canalicular
actin-associated protein. Recombinant ezrin produced in either Sf9 ce
lls or bacteria also bound R(II). Recombinant radixin and moesin, ezri
n-related proteins, also bound R(II) in blot overlay. Analysis of reco
mbinant truncations of ezrin mapped the R(II) binding site to a region
between amino acids 373 and 439. This region contained a lit-aminoaci
d amphipathic alpha-helical putative R(II) binding region. A synthetic
peptide containing the amphipathic helical region (ezrin(409-438)) bl
ocked R(II) binding to ezrin, but a peptide with a leucine to proline
substitution at amino acid 421 failed to inhibit R(II) binding. In mou
se fundic mucosa, R(II) immunoreactivity redistributed from a predomin
antly cytosolic location in resting parietal cells, to a canalicular p
attern in mucosa from animals stimulated with gastrin. These results d
emonstrate that ezrin is a major AKAP in gastric parietal cells and ma
y function to tether type II A-kinase to a region near the secretory c
analiculus.