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Objective:To obtain recombinant D227A mutation Staphylococcal enterotoxin A protein(rSEAD227A) with low toxicity but still retain its immunological activity and high purity. Methods: The SEA gene containing D227A mutation was cloned by PCR. By constructing pET44a-SEAD227Avector and transfecting the expression strain Rosetta, inclusion bodies were solubilized with guanidium hydrochloride and refolded by gradient dialysis;proteins were purified using StrepⅡ affinity chromatography,and identified by Western blot and high performance liquid chromatography-mass spectrometry(LC-MS/MS). Results: The D227A mutation of SEA was cloned and the expression system of Rosetta-rSEAD227Awas constructed. The purified rSEAD227Aprotein was obtained by refolding with gradient dialysis and affinity purification. LC-MS/MS analysis confirmed that the tryptic digested rSEAD227A peptide sequences matched the sequences of SEA in the database. Conclusion: The rSEAD227A protein in high purity was obtained,which provided the ex-perimental basis for further basic research and clinical application of SEA.
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<p><b>OBJECTIVE</b>To explore the establishment of the mimetic aging effect in guinea pigs induced by D-galactose, and to detect the biological indicatrix associated with hearing loss and provide a new tool for molecular pathogenesis of hearing loss.</p><p><b>METHODS</b>Total of 51 guinea pigs were randomly divided into three groups: group A (model aging group, n = 25), which were injected with D-galactose (200 mgxkg(-1)xd(-1)) by intra peritoneum for 6 weeks, group B (model control group, n = 18), which were given the same amount of saline only, and group C (vacant group, n = 15) were not treated. Then, The guinea pigs in group A and B were exposed in noise for 8 days, 8 hours once a day. Auditory brainstem response (ABR) was used to test the hearing threshold of guinea pigs thrice, first before the drug administered, then after 6 weeks the drug used, third after noise exposure. And colorimetry was used to analyze the activity of superoxide dismutase (SOD) and malon dialdehyde (MDA) in brain and liver tissue. The DNA of inner ear tissue was harvested and amplified fragment length polymorphism (AFLP) was used to detect the differential polymorphic markers.</p><p><b>RESULTS</b>After injection, there was no significant difference in elevation of ABR threshold between the group A and group B (t = 1.14, P > 0.05). However, exposure of noise later, elevation in ABR threshold of (22.97 +/- 10.56) dB peSPL was observed in group A, and (14.16 +/- 7.36) dB peSPL in group B. The was significant difference in variation of hearing threshold between group A and group B (t = 2.78, P < 0.05). The activity of SOD in brain and liver tissue in group A was lower than that in group B. the level of MDA was opposite between group A and group B. The difference between group A and group B was significant (P < 0.01). A differential polymorphic marker was observed by AFLP.</p><p><b>CONCLUSIONS</b>The mimetic aging effect of the guinea pigs can be induced by D-galactose, and this model can not directly induce the hearing loss. The differential polymorphic marker possibly act as a predisposing factor which can greatly enhance the sensitivity of the ear to the noise.</p>