Crystal structure of phenylacetic acid degradation protein PaaG from Thermus thermophilus HB8
Crystal structure of phenylacetic acid degradation protein PaaG from Thermus thermophilus HB8
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DOI：
10.1002/prot.22455
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发表时间：
2009-09-01
影响因子：
2.9
通讯作者：
Miki, Kunio
中科院分区：
文献类型：
--
作者：
Kichise, Tomoyasu;Hisano, Tamao;Miki, Kunio
苯乙酸的微生物降解通过混合途径进行，包括形成辅酶A硫酯、环羟基化、非氧化开环和β-氧化样反应。苯乙酸降解蛋白PaaG是巴豆酸酶超家族的成员，并且是候选的非氧化开环酶。以1.85埃的分辨率测定了来自嗜热栖热菌HB 8的PaaG的晶体结构。PaaG由三个相同的亚基通过局部三重对称性相关。单体由具有巴豆酸酶超家族特征性折叠的螺旋和螺旋结构域组成。一个推定的活性位点残基，Asp 136，位于活性位点空腔中，并被几个疏水性和亲水性残基包围。活性位点腔足够大以容纳环形衬底。两个构象观察螺旋H2位于邻近的活性位点。H2在两个亚基中在Asn 81处扭结，而在另一个亚基中在Leu 77处扭结，并且Tyr 80的侧链更接近Asp 136。这表明PaaG的催化反应可能在活性位点发生较大的构象变化。Asp 136是活性位点中唯一保守的极性残基。它位于与4-氯苯甲酰辅酶A脱卤酶和过氧化物酶体Delta（3），Delta（2）-烯酰辅酶A异构酶相同的位置，表明PaaG可能通过Delta（3），Delta（2）-烯酰辅酶A异构酶样机制进行异构化或开环反应。
Microbial degradation of phenylacetic acid proceeds via the hybrid pathway that includes formation of a coenzyme A thioester, ring hydroxylation, non-oxygenolytic ring opening, and beta-oxidation-like reactions. A phenylacetic acid degradation protein PaaG is a member of the crotonase superfamily, and is a candidate non-oxygenolytic ring-opening enzyme. The crystal structure of PaaG from Thermus thermophilus HB8 was determined at a resolution of 1.85 angstrom. PaaG consists of three identical subunits related by local three-fold symmetry. The monomer is comprised of a spiral and a helical domain with a fold characteristic of the crotonase superfamily. A putative active site residue, Asp136, is situated in an active site cavity and surrounded by several hydrophobic and hydrophilic residues. The active site cavity is sufficiently large to accommodate a ring substrate. Two conformations are observed for helix H2 located adjacent to the active site. Helix H2 is kinked at Asn81 in two subunits, whereas it is kinked at Leu77 in the other subunit, and the side chain of Tyr80 is closer to Asp136. This indicates that catalytic reaction of PaaG may proceed with large conformational changes at the active site. Asp136 is the only conserved polar residue in the active site. It is located at the same position as those of 4-chlorobenzoyl-CoA dehalogenase and peroxisomal Delta(3),Delta(2)-enoyl-CoA isomerase, indicating that PaaG may undergo isomerization or a ring-opening reaction via a Delta(3),Delta(2)-enoyl-CoA isomerase-like mechanism.