Glutamate decarboxylase (GAD) can catalyze the decarboxylation of glutamate into γ-aminobutyrate (GABA) and is the only enzyme of GABA biosynthesis. Improving GAD activity and thermostability will be helpful for the highly efficient biosynthesis of GABA. According to the Ramachandran plot information of GAD 1407 three-dimensional structure from Lactobacillus brevis CGMCC No. 1306, we identified the unstable site K413 as the mutation target, constructed the mutant GAD by site-directed mutagenesis and measured the thermostability and activity of the wide type and mutant GAD. Mutant K413A led to a remarkably slower inactivation rate, and its half-life at 50 °C reached 105 min which was 2.1-fold higher than the wild type GAD1407. Moreover, mutant K413I exhibited 1.6-fold higher activity in comparison with the wide type GAD1407, although it had little improvement in thermostability of GAD. Ramachandran plot can be considered as a potential approach to increase GAD thermostability and activity.
Glutamate Decarboxylase ; metabolism ; Half-Life ; Industrial Microbiology ; Lactobacillus brevis ; enzymology ; Mutagenesis, Site-Directed ; Mutation ; Temperature

Objective To study the changes of plasma cystatin C level (PcyC),and evaluate the effects of the joint use of atorvastatin and probucol on PcyC and severity of coronary lesion in patients with borderline lesion of coronary artery.Methods One hundred and thirty consecutive patients with borderline coronary lesion assessed by quantitative coronary angiography were enrolled into borderline coronary lesion group (BCL),and another 136 subjects without coronary lesion were enrolled as controls (CTR).And in the meantime,the subjects in BCL group were randomized (closed envelope method) into routine treatment subgroup ( RTT,n =60),and combined treatment subgroup in which patients were treated with atorvastatin 20 mg plus probucol 1.0 g daily in addition to routine medication ( CBT,n =70) for 6 months.There were no statistical differences in basic clinical features between two subgroups.PcyC,high-sensitive C-reactive protein (hs-CRP),total cholesterol (TC),low-density lipoprotein cholesterol (LDL-C),high-density lipoprotein cholesterol ( HDL-C ) and triglycerides (TG) were determined.Of them,104 patients in BCL group rechecked by coronary angiography.Comparison of biomarkers carried out between two groups by using a number of independent-sample t-test and analysis of variance.For enumeration data,chi-square test was used to compare mean values of biomarkers between groups. P ＜ 0.05 was considered statistically significant.Results PcyC levels were significantly higher in BCL group than those in CTR group ( P ＜ 0.05 ).Compared with RTT subgroup,levels of PcyC,TC,LDL-C,TG and hs-CRP were more significantly decreased in CBT subgroup (P ＜ 0.05,P ＜ 0.01 ).Moreover,there was a trend of slight decrease in the mean percent of stenosis (MPS) of coronary artery with borderline lesion in RTT subgroup treated for 6 months,whereas more marked decrease in the MPS of coronary artery with borderline coronary lesion in CBT subgroup treated for 6 months ( P ＞ 0.05 ; P ＜ 0.05 ).Conclusions Cystatin C plays an important role in the pathogenesis of coronary artery,and PcyC is associated with severity of coronary lesion,the combination of atorvastatin and probucol decreases the PcyC level,and it may be the treatment of choice for borderline lesion of coronary artery.

Objective To explore whether ultrasound-mediated microbubbles destruction could enhance anti-sense RNA transfection and expression. Methods Phospholamban antisense RNA eukaryon vector PcDNA 4. 1-asPLB was successfully constructed and it was transfected into cardiac myocytes by various methods including calcium phosphate precipitation, ultrasound exposure and ultrasound-mediated microbubbles destruction. The expression of PLB and sarcoplasmic retculum Ca2+ ATPase (SERCA2a) in cardiac myocytes was tested by RT-PCR and western blot. Results The transfection and expression of PcDNA 4. 1-asPLB increased significantly in cells treated with ultrasound-mediated microbubbles destruction compared to other transfer groups( P ＜0.05). The expression of PLB was inhibited specifically after cardiac myocytes were transfected with PcDNA 4. 1-asPLB. There was no change of PLB expression after cardiac myocytes transfected with PcDNA 4. 1 ( P ＜0.05). Though the expression of SERCA2a never exhibited any changes after PcDNA 4. 1-asPLB transfection, the PLB/SERCA2a ratio decreased markedly. Conclusions As a highly effective antisense RNA transfer method, ultrasound-mediated microbubbles destruction can enhance the transfection and expression of the PcDNA 4. 1-asPLB significantly. The PcDNA4. 1-asPLB transfection inhibits the expression of PLB and result in decrease of PLB/SERCA2a ratio in cardiac myocytes.

Objective To evaluate the relationship between plasma cystatin C concentration (PcyC) and coronary artery diseases (CAD). Method A total of 126 subjects with CAD evidenced by coronary angiography admitted from April 2007 to March 2009 were divided into three groups: stable angina pectoris (SAPs, n = 34),unstable angina pectoris (UAPs, n = 56) and acute myocardial infarction (AMIs, n = 36), according to the diag-nostic criteria of CAD set by WHO. Another 34 subjects without CAD were taken as controls. There were no statis-tical differences in demographics among four groups. Serum lipids profile, uric acid (UA), PcyC and high-sensi-tive C-reactive protein (hs-CRP) were determined. And in the meantime, all patients were followed up for six months and adverse cardiovascular events were recorded. Comparisons were made between groups with a number of independent-sample t -tests. Data were processed with analysis of variance to test the differences in means among four groups, and the means were compared with chi-square test. Statistical significance was established at a P val-ue of less than 0.05. Results Cystatin C levels were significantly higher in UAPs than that in SAPs and in controls (P < 0.05), but were much lower than that in AMIs (P < 0.05). And much higher concentration of hs-CRP was found in UAPs (P < 0.05) and in AMIs (P < 0.01). Cystatin C was positively and significantly corre-lated with age, hs-CRP, WBC, creatinine and UA (r > 0, P < 0.05), whereas a significantly negative correla-tion with high-density lipoprotein cholesterol was found (r = - 0.227, P < 0.05). These coefficients were obvi-ously high for creatinine (r = + 0. 612), and WBC (r = + 0.459). During the period of six-month follow-up, 26 patients with adverse cardiovascular events were found, and had significantly higher cystatin C levels than 22 con-trols at admission (P < 0.01). Conclusions Cystatin C plays a pivotal role in the course of CAD, and the PcyC is a strong predictor for the risk of cardiovascular events.

Glutamate decarboxylase, a unique pyridoxal 5'-phosphate-dependent enzyme, catalyzes α-decarboxylation of L-glutamate to γ-aminobutyrate. However, glutamate decarboxylase from different sources has the common problem of poor thermostability that affects its application in industry. In this study, proline was introduced at 13 different positions in glutamate decarboxylase by using the design strategy of homologous sequence alignment between Thermococcus kodakarensis and Lactobacillus brevis CGMCC No.1306. A mutant enzyme G364P with higher thermostability was obtained. Compared to the wild type, thermostability of the mutant G364P was significantly improved, the half-life time (t1/2) at 55 °C and the semi-inactivation temperature (T₅₀ ¹⁵) of the mutant G364P increased 19.4 min and 5.3 °C, respectively, while kcat/Km of the mutant enzyme remained nearly unchanged. Further analysis of their thermostability by molecular dynamics simulations were performed. The root mean square deviation of G364P and root mean square fluctuation in the loop region including G364 were lower than the wild type at 313 K for 10 ns, and G364P increased one hydrophobic interaction in the loop region. It proves that mutation of flexible 364-Gly to rigid proline endows glutamate decarboxylase with enhanced thermostability.
Glutamate Decarboxylase ; Glutamic Acid ; Lactobacillus brevis ; Molecular Dynamics Simulation ; Proline