Calcium-dependent association of a protein complex with the lymphocyte plasma membrane: probable identity with calmodulin-calcineurin.

Open Access
Publisher Website
Google Scholar
Abstract
A protein complex is shown to participate in a Ca-dependent association with plasma membranes purified either from pig mesenteric lymph node lymphocytes or from human lymphoblastoid cell lines. Plasma membranes prepared in the presence of Ca possess this complex; those prepared in the absence of Ca (5 mM EGTA [ethylene glycol bis(.beta.-aminoethyl ether)N,N,N'',N''-tetraacetic acid]) do not. The complex associates itself with the inner cytoplasmic surface of the plasma membrane. This complex is referred to as the acidic protein band because of its location during migration upon alkaline-urea gel electrophoresis. The complex dissociates from the plasma membrane during electrophoresis on 8-M urea gels, irrespective of Ca levels during the electrophoresis; at intermediate urea concentrations (4-6 M), the complex is not dissociated in the presence of Ca. Upon purification of the acidic protein band, SDS [sodium dodecyl sulfate] acrylamide gel electrophoresis, immunoblotting and radioimmunoassay techniques suggest that the acidic protein band is composed of a least 4 peptides (designated 68K, 59K, 20K, 20K): 2 of these (68K, 20K) are immunopositive for calcineurin and 1 (20K) is immunopositive for calmodulin. Immunoblots of urea gels also indicate that the calcineurin H chain (68K) can also appear at 3 different locations on the urea gel. Patches and caps induced in human peripheral blood lymphocytes by fluorescein-conjugated goat anti-human IgG are not coincident with the location of calcineurin, which remains distributed throughout the cell.