RESUMO
The primary structure of the alpha-subunit of the adenylate cyclase-inhibiting G-protein (Gi) has been deduced from the nucleotide sequence of cloned DNA complementary to the bovine cerebral mRNA encoding the polypeptide. A much higher degree of amino acid sequence homology is observed between the alpha-subunits of Gi and transducin (68%) than between those of Gi and the adenylate cyclase-stimulating G-protein (Gs) (43%) or between those of transducin and Gs (42%).
Assuntos
Inibidores de Adenilil Ciclases , DNA , Proteínas de Ligação ao GTP/genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Química Encefálica , Bovinos , DNA Recombinante , Proteínas de Membrana/genética , Hibridização de Ácido Nucleico , Fragmentos de Peptídeos , Poli A/genética , RNA/genética , RNA Mensageiro , TransducinaAssuntos
Endopeptidases , Endotoxinas/farmacologia , Precursores Enzimáticos , Teste do Limulus , Sequência de Aminoácidos , Animais , Fatores de Coagulação Sanguínea/metabolismo , Proteínas Sanguíneas/isolamento & purificação , Géis , Caranguejos Ferradura/metabolismo , Lipopolissacarídeos/antagonistas & inibidores , Peso MolecularRESUMO
The complete amino acid sequence of the coagulogen from hemocyte lysates of Limulus polyphemus has been determined by sequencing the peptides obtained from tryptic, chymotryptic, staphylococcal protease V8 and lysyl endopeptidase digestions. These results established the following sequence: (formula; see text) Limulus coagulogen consists of a single chain with a total of 175 amino acid residues and the molecular weight is calculated to be 19,675. It contains 16 half-cystines in disulfide linkages, with 5 half-cystines located in a cluster in the COOH-terminal 14 residues. The sequence of Limulus coagulogen is very close to that for the coagulogen of Tachypleus tridentatus (Japanese horseshoe crab), having 69% sequence homology. The 16 half-cystines of these coagulogens are in the same positions, suggesting a very similar conformation. Moreover, the COOH-terminal tripeptide regions of the A chain (from the NH2-terminal end to Arg-18) and peptide C (from Lys-19 to Arg-46), both of which seem to interact with a Limulus clotting enzyme to liberate peptide C, are completely conserved. From secondary structure predictions by the method of Chou and Fasman (Chow, P.Y., and Fasman, G. D. (1974) Biochemistry 13, 211-222), the coagulogen appears to contain an alpha-helical region in the peptide C segment, released by the clotting enzyme, suggesting a marked conformational change in the transformation of the coagulogen to the coagulin gel. beta-sheet and reverse turn regions are distributed in the B chain segment (from Gly-47 to the COOH-terminal end). It is likely that the 16 half-cystines and abundant beta-sheet structure make the coagulogen molecule compact.