Three-dimensional structure of the flavoenzyme Acyl-CoA oxidase-II from rat liver, the peroxisomal counterpart of mitochondrial Acyl-CoA dehydrogenase
Three-dimensional structure of the flavoenzyme Acyl-CoA oxidase-II from rat liver, the peroxisomal counterpart of mitochondrial Acyl-CoA dehydrogenase
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DOI：
10.1093/oxfordjournals.jbchem.a003111
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发表时间：
2002-03-01
影响因子：
2.7
通讯作者：
Miura, R
中科院分区：
文献类型：
--
作者：
Nakajima, Y;Miyahara, I;Miura, R
酰辅酶A氧化酶(ACO)催化脂肪酸过氧化体β氧化的第一步，也是决定反应速度的第一步。ACO-II是大鼠肝脏ACO的两种形式之一(ACO-I和ACO-II)，它的晶体结构已被解析，并在2.2a分辨率下精炼到20.6%的R因子。该酶是一种同源二聚体，亚基的多肽链被折叠成N-末端的α结构域、β-结构域和C-末端的α结构域。X-射线分析表明，ACO-II少C端221个残基的整体折叠与中链酰基辅酶A脱氢酶(MCAD)相似。然而，与MCAD中的那些相比，N-末端的α-和β-结构域相对于C-末端的α-结构域旋转了13度，从而产生了一个又长又大的缝隙，容纳了辅因子FAD和底物酰基-CoA。FAD结合在β-末端和C-末端结构域之间的缝隙上，其二磷酸腺苷部分与分子的另一个亚基广泛相互作用。FAD的Flavin环位于活性部位，其表面附着在β结构域上，并被活性部位残基包围，其方式与MCAD中发现的类似。然而，由于失去了在MCAD中发现的一些与黄文环的重要氢键，残基与黄素环的相互作用很弱。C-末端α结构域的催化残基Glu421似乎离黄素环太远，无法提取底物酰基-CoA的α-质子，这表明当底物结合时，C-末端结构域移动到关闭活性部位。黄素的嘧啶部分暴露在溶剂中，很容易受到分子氧的攻击，而MCAD中的嘧啶部分则受到溶剂的保护。结合脂肪酰链的缝隙长28埃，宽6埃，大到足以容纳C23酰链。
Acyl-CoA oxidase (ACO) catalyzes the first and rate-determining step of the peroxisomal beta-oxidation of fatty acids. The crystal structure of ACO-II, which is one of two forms of rat liver ACO (ACO-I and ACO-II), has been solved and refined to an R-factor of 20.6% at 2.2-a resolution. The enzyme is a homodimer, and the polypeptide chain of the subunit is folded into the N-terminal alpha-domain, beta-domain, and C-terminal alpha-domain. The X-ray analysis showed that the overall folding of ACO-II less C-terminal 221 residues is similar to that of medium-chain acyl-CoA dehydrogenase (MCAD). However, the N-terminal alpha- and beta-domains rotate by 13degrees with respect to the C-terminal alpha-domain compared with those in MCAD to give a long and large crevice that accommodates the cofactor FAD and the substrate acyl-CoA. FAD is bound to the crevice between the beta- and C-terminal domains with its adenosine diphosphate portion interacting extensively with the other subunit of the molecule. The flavin ring of FAD resides at the active site with its si-face attached to the beta-domain, and is surrounded by active-site residues in a mode similar to that found in MCAD. However, the residues have weak interactions with the flavin ring due to the loss of some of the important hydrogen bonds with the flavin ring found in MCAD. The catalytic residue Glu421 in the C-terminal alpha-domain seems to be too far away from the flavin ring to abstract the alpha-proton of the substrate acyl-CoA, suggesting that the C-terminal domain moves to close the active site upon substrate binding. The pyrimidine moiety of flavin is exposed to the solvent and can readily be attacked by molecular oxygen, while that in MCAD is protected from the solvent. The crevice for binding the fatty acyl chain is 28 Angstrom long and 6 Angstrom wide, large enough to accommodate the C23 acyl chain.