Analysis of LACS Enzyme Activity
Background
脂肪酸β氧化过程(β-oxidation)在动物组织的线粒体发生的脂肪酸代谢通路,可概括为活化、转移、β氧化及最后经三羧酸循环被彻底氧化生成CO~2~和H~2~O,并释放能量等四个阶段。脂酰辅酶A合成酶(acyl coA synthetase;EC.6.2.1.3),又称为脂肪酸硫激酶(fatty acid thiokinase)或脂酰辅酶A连接酶(acyl coA ligase),是脂肪酸进入β-氧化前的活化所必需:在ATP、CoA-SH、Mg2+存在下,催化饱和或不饱和直链脂肪酸分子(C4)连接辅酶A合成相应的脂酰辅酶A。
脂酰辅酶A合成酶分成三种底物特异性的种类:小于4个碳(C4)的短链脂酰辅酶A合成酶(acetyl-CoA synthetase),介于4至12个碳(C4-C12)的中链脂酰辅酶A合成酶(butyryl-CoA synthetase),和大于12个碳(C12)的长链脂酰辅酶A合成酶(palmitoyl CoA synthetase)。
基于长链脂肪酸棕榈酸(palmitate)和辅酶A在长链脂酰辅酶A合成酶(LACS)的作用下,产生棕榈酰辅酶A(palmitoyl-CoA)后,通过肌激酶(myokinase)、丙酮酸激酶(pyruvate kinase)和乳酸脱氢酶(lactic dehydrogenase)系统,测定还原型烟酰胺腺嘌呤二核苷酸(reduced nicotinamide adenine dinucleotide;NADH)转化为氧化型烟酰胺腺嘌呤二核苷酸(oxidized nicotinamide adenine dinucleotide;NAD)的变化(340nm波长),来定量分析长链脂酰辅酶A合成酶的活性。
LACS反应过程:
Protein expression
利用原核表达的方法,纯化浓缩获得所需要的蛋白。
- 扩增目的基因的全长,并克隆至pET28b载体中,然后转化至表达宿主菌株BL21 Rosetta。
- 用0.05 mM IPTG(isopropyl β-D-1-thiogalactopyranoside)诱导OD600=0.3-0.6的菌株。16°C,120 rpm过夜培养16 h。
- 收集及破碎菌株,用Ni-NTA beads进行纯化,若浓度不够,还需进行浓缩。
Reagents prepare
在正式开始实验前,需要准备好所需的试剂,方便实验进行。主要为预混液premix以及各底物母液配置。
预混溶液的母液配置
其中MgCl~2~和KCl可以称量配制500 ml所需的质量,即分别为2.033*5=10.165 g和0.3728*10=3.728 g。然后,将其加入至500 ml Tris-HCl溶液中,配制成含1 M Tris-HCl(pH7.5)、100 mM MgCl2和100 mM KCl的母液。这三者最终工作液浓度均是稀释10倍,且不会反应。
Stock solution | Volume,mol*V*MW = mass(g) |
---|---|
1 M Tris-HCl (pH7.5) MW: 121.1 | 500 mL, 1*0.5*121.1=60.55 |
200 mM dithiothreitol MW: 154.3 | 5 mL, 0.005*0.2*154.3=0.1543 |
250 mM ATP MW: 551.4 | 4.0 ml, 0.25*0.004*507.18=0.5514 |
100 mM MgCl2 MW: 203.3 | 100 mL, 0.1*0.1*203.3=2.033 |
100 mM KCl MW: 74.55 | 50 mL , 0.1*0.05*74.55=0.3728 |
50 mM CoA MW: 767.5 | 4 mL, 0.05*0.004*767.5=0.0154 |
50 mM NADH MW: 741.6 | 1 mL, 0.05*0.001*741.6=0.0371 |
100 mM phosphoenolpyruvate salt MW: 267.22 | 2.5 mL, 0.1*0.0025*206.13=0.0515 |
底物母液配置
脂肪酸根据碳链长度分为短链脂肪酸(SCFA:小于6个C,挥发性脂肪酸)、中链脂肪酸(MCFA:6-12个C,主要是辛酸C8和癸酸C10)和长链脂肪酸(LCFA:大于12个C)。一般C原子小于10的低级脂肪酸易溶于水,随着C原子继续增加,溶解度减小,溶或者不溶于水,但溶于有机溶剂。除特殊说明,可以使用5% Triton X-100来配制5 mM的C~10~以上的脂肪酸底物。
Substrates | MW,mol,Volume | mol*V*MW=mass (g) |
---|---|---|
Sodium acetate | C2:0 MW: 82.03 50 mM 10 mL | 0.05*0.01*82.03=0.041 |
Sodium butyrate | C4:0 MW: 110.09 5 mM 10 mL | 0.005*0.01*110.09=0.0055 |
Sodium hexanoate | C6:0 MW: 138.14 5mM 10mL | 0.005*0.01*138.14=0.0069 |
Sodium octanoate | C8:0 MW:166.19. 5mM 10mL | 0.005*0.01*166.19=0.0083 |
Sodium decanoate | C10:0 MW:194.25. 5mM 10mL | 0.005*0.01*194.25=0.0097 |
Sodium dodecanoate 月桂酸钠 | C12:0 MW:222.30. 5mM 10mL | 0.005*0.01*222.30=0.0111 |
Sodium myristate 肉豆蔻酸钠 | C14:0 MW:250.35. 5mM 10mL | 0.005*0.01*250.35=0.0125 |
Sodium palmitate 棕榈酸钠 | C16:0 MW:278.41. 5mM 10mL | 0.005*0.01*278.41=0.0139 |
Sodium stearate 硬脂酸钠 | C18:0 MW:306.46. 5mM 10mL | 0.005*0.01*306.46=0.0153 |
Sodium linoleate 亚油酸钠 | C18:2 MW:302.4. 5mM 10mL | 0.005*0.01*302.4=0.0151 in 10% TritonX-100 |
12-oxo-phytodienoic acid (C18H28O3) | OPDA MW: 292.4 (1ug/uL in 100% ethonl) | Take 50uL to dry down and resuspend in 100uL 10% TritonX-100 will give the concentration of 1709.9uM, 1.71mM. |
Dinor-12-oxophytodienoic Acid (C16H24O3) | OPDA-2 MW:264.4 | |
Tridecanoic acid | C13:0 | |
Undecanoic acid | C11:0 | |
11- Methyldodecanoic acid (11- methyllauric acid) | CAS:5681-98-1 |
Enzyme activity assay
- 5% Triton X-100(v/v)配制5 mM的脂肪酸底物。
- 准备酶活分析的预混溶液,均分为95 µl至每个96孔UV板。
Stock solution | Working concentration | Volume in 10 ml | Volume in 7 ml |
---|---|---|---|
1M Tris-HCl(pH7.5) MW:121.1 | 0.1M Tris-HCl(pH7.5) MW:121.1 | 1 mL | 0.7 mL |
200 mM dithiothreitol MW:154.3 | 2 mM dithiothreitol MW:154.3 | 100 uL | 70 uL |
250 mM ATP MW: 551.4 | 5 mM ATP 551.4 | 200 uL | 140 uL |
100 mM MgCl2 (included in Tris) | 10 mM MgCl2 | 0 mL | |
100 mM KCl (included in Tris) | 10 mM KCl | 0 mL | |
50 mM CoA 767.5 | 0.5mM CoA 767.5 | 100uL | 70 uL |
50 mM NADH 741.6 | 0.25 mM NADH 741.6/ 1mM | 50 uL/200 uL | 35 uL/140 uL |
100 mM phosphoenolpyruvate salt MW: 267.22 | 1 mM phosphoenolpyruvate salt MW: 267.22 | 100 uL | 70 uL |
Myokinase M3003 Sigma (2268.11 unit/mg, 3 mg/mL) | 20 units myokinase | 40 uL | 28 uL |
Pyruvate kinase 10128155001 Roche (200 units/mg at RT, 10 mg/mL) | 10 units pyruvate kinase | 50 uL | 35 uL |
Lactate dehydrogenase 10127230001 Roche (550 units/mg at RT, 5 mg/mL) | 10 units lactate dehydrogenase | 40 uL | 28 uL |
5 mM fatty acyl substrate | 250 uM fatty acyl substrate | 5 uL in 100 uL reaction for 1/10 D | 2 uL in 100 uL for 1/50 dilution |
H2O | 8.3 mL | 5.75 mL |
- 加入5 µl(1-2 µg)纯化的目的蛋白,开始反应。
- 在酶标仪中,设置30°C的温度,OD~340nm~处读数40 min,每隔5 min读取一次。
Reference
- Patel SS and Walt DR. (1987). Substrate specificity of acetyl coenzyme A synthetase. Journal of Biological Chemistry 262: 7132–7134.
- Fan PX, Wang PP, Lou YR, Leong BJ, Moore BM, Schenck CA, Combs R, Cao PF, Brandizzi F, Shiu SH, and Last RL. (2020). Evolution of a plant gene cluster in Solanaceae and emergence of metabolic diversity. eLife 9: e56717.