RESUMO
The expression of sarcoplasmic reticulum SERCA1a Ca2+-ATPase wild-type and D351E mutants was optimized in yeast under the control of a galactose promoter. Fully active wild-type enzyme was recovered in yeast microsomal membrane fractions in sufficient amounts to permit a rapid and practical assay of ATP hydrolysis and phosphoenzyme formation from ATP or Pi. Mutant and wild-type Ca2+-ATPase were assayed for phosphorylation by Pi under conditions that are known to facilitate this reaction in the wild-type enzyme, including pH 6.0 or 7.0 at 25°C in the presence of dimethylsulfoxide. Although glutamyl (E) and aspartyl (D) residue side chains differ by only one methylene group, no phosphoenzyme could be detected in the D351E mutant, even upon the addition of 40 percent dimethylsulfoxide and 1 mM 32Pi in the presence of 10 mM EGTA and 5 mM MgCl2. These results show that in the D351E mutant, increasing hydrophobicity of the site with inorganic solvent was not a sufficient factor for the required abstraction of water in the reaction of E351 with Pi to form a glutamylphosphate (P-E351) phosphoenzyme moiety. Mutation D351E may disrupt the proposed alignment of the reactive water molecule with the aspartylphosphate (P-D351) moiety in the phosphorylation site, which may be an essential alignment both in the forward reaction (hydrolysis of aspartylphosphate) and in the reverse reaction (abstraction of water upon formation of an aspartylphosphate intermediate).
Assuntos
Animais , Coelhos , Mutação/genética , Fosfatos/metabolismo , Saccharomyces cerevisiae/genética , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/genética , Retículo Sarcoplasmático/enzimologia , Regulação Fúngica da Expressão Gênica , Vetores Genéticos , Fosforilação , Saccharomyces cerevisiae/metabolismo , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/metabolismoRESUMO
We want to construct a yeast expression system for thymosin a1 (Ta1) to make the orally administered Ta1 preparation possible. The whole Ta1 DNA fragment was obtained by PCR. After being digested with restriction enzymes, it was cloned into pYES2 vector. Sequencing was performed to identify the recombinant. The sequence of Ta1 in recombinant coincided with the original one reported in Genbank. When pYES2-Ta1 plasmid was transformed into yeast, galactose instead of glucose was used to induce Ta1 expression. Western blot was performed to identify the quality of the expressed Ta1. Dried yeast containing pYEST2-Ta1 was fed to Balb/c mice whose immunities were inhibited by cyclophosphamide in advance. Synthesized Ta1 peptide was used as positive control and empty yeast was used as negative control. Compared with the negative control group, both dried yeast containing pYEST2-Ta1 and synthesized Ta1 peptide can significantly increase the CD8+ level (22.74±1.09 and 18.77±4.72 vs 7.49±2.14, p<0.01), while both of them had little effect on the CD4+ lymphocytes (61.86±6.94 and 65.91±4.78 vs 57.93±10.40, p>0.05). We concluded that a high effective yeast expression system for Ta1 was constructed successfully and the Ta1 protein expressed by this system can improve CD8+ level in immune inhibited mice.