RESUMO
A phosphorylatable protein band of about 94 kDa (as judged by SDS-PAGE) which co-purifies and co-immunoprecipitates with Golgi apparatus casein kinase (G-CK) from rat lactating mammary gland has been shown by mass spectrometric sequence analysis to be identical or very similar to the glucose-regulated protein, GRP94. GRP94 is also readily phosphorylated by G-CK (K(m)=0.2 microM) at seryl sites which are different from the sites affected by casein kinase-2 (CK2) in the same protein. A study with peptide substrates would indicate that the G-CK sites in GRP94 conform to the motif S-R/K-E-X (X being different from D and E) which is not recognized by CK2.
Assuntos
Complexo de Golgi/enzimologia , Proteínas de Choque Térmico HSP70/metabolismo , Lactação , Glândulas Mamárias Animais/metabolismo , Proteínas de Membrana/metabolismo , Proteínas Quinases/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Animais , Caseína Quinase II , Caseína Quinases , Feminino , Proteínas de Choque Térmico HSP70/química , Proteínas de Choque Térmico HSP70/isolamento & purificação , Cinética , Glândulas Mamárias Animais/enzimologia , Espectrometria de Massas , Proteínas de Membrana/química , Proteínas de Membrana/isolamento & purificação , Microssomos Hepáticos , Dados de Sequência Molecular , Peso Molecular , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Fosforilação , Fosfosserina/metabolismo , Testes de Precipitina , Ligação Proteica , Proteínas Quinases/isolamento & purificação , Proteínas Serina-Treonina Quinases/metabolismo , Ratos , Especificidade por SubstratoRESUMO
Rat liver plectin was found to be mainly associated with plasma membrane fractions enriched in junctional complexes. The membrane-associated plectin has been partially isolated. Plectin co-purifies with a 200 kDa polypeptide which, on the basis of sequence homology, has been identified as a myosin like-protein. The interaction of mu-calpain with liver plectin has been investigated. Plectin is very sensitive to mu-calpain and is digested to give a fragment of 240 kDa.