Board P G, Coggan M, Wilce M C, Parker M W
John Curtin School of Medical Research, Australian National University, Canberra.
Biochem J. 1995 Oct 1;311 ( Pt 1)(Pt 1):247-50. doi: 10.1042/bj3110247.
A consistent feature of the Alpha-, Mu- and Pi-class glutathione transferases (GSTs) is the presence near the N-terminus of a tyrosine residue that contributes to the activation of glutathione. While this residue appears to be conserved in many Theta-class GSTs, its absence in some suggested that the Theta-class GSTs may have a significantly different structure or catalytic mechanism. The elucidation of the crystal structure of the Theta-class GST from the Australian sheep blowfly, Lucilia cuprina, has indicated that a serine residue rather than a tyrosine residue can form a hydrogen bond with the glutathionyl sulphur atom. The present studies show that mutation of Ser-9 to alanine substantially inactivates the L. cuprina GST, confirming its importance in the reaction mechanism. As this serine is conserved in all Theta-class enzymes reported so far, it seems that an active-site serine is a significant factor that distinguishes the Theta-class GSTs from members of the Alpha-, Mu- and Pi-class isoenzymes.
α-、μ-和π-类谷胱甘肽转移酶（GSTs）的一个共同特征是在N端附近存在一个酪氨酸残基，该残基有助于谷胱甘肽的活化。虽然这个残基在许多θ-类GSTs中似乎是保守的，但在一些酶中没有该残基，这表明θ-类GSTs可能具有显著不同的结构或催化机制。对澳大利亚羊蝇Lucilia cuprina的θ-类GST晶体结构的阐明表明，是一个丝氨酸残基而非酪氨酸残基能与谷胱甘肽硫原子形成氢键。目前的研究表明，将Ser-9突变为丙氨酸会使铜绿丽蝇GST基本失活，证实了其在反应机制中的重要性。由于该丝氨酸在目前报道的所有θ-类酶中都是保守的，所以活性位点丝氨酸似乎是区分θ-类GSTs与α-、μ-和π-类同工酶成员的一个重要因素。
