Crystal structures of complexes of the branched-chain aminotransferase from deinococcus radiodurans with α-Ketoisocaproate and L-glutamate suggest the radiation resistance of this enzyme for catalysis

Chung De Chen, Chih Hao Lin, Phimonphan Chuankhayan, Yen Chieh Huang, Yin Cheng Hsieh, Tien Feng Huang, Hong Hsiang Guan, Ming Yih Liu, Wen Chang Chang, Chun Jung Chena

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17 引文 斯高帕斯(Scopus)

摘要

Branched-chain aminotransferases (BCAT), which utilize pyridoxal 5=-phosphate (PLP) as a cofactor, reversibly catalyze the transfer of the α-amino groups of three of the most hydrophobic branched-chain amino acids (BCAA), leucine, isoleucine, and valine, to α-ketoglutarate to form the respective branched-chain α-keto acids and glutamate. The BCAT from Deinococcus radiodurans (DrBCAT), an extremophile, was cloned and expressed in Escherichia coli for structure and functional studies. The crystal structures of the native DrBCAT with PLP and its complexes with L-glutamate and α-ketoisocaproate (KIC), respectively, have been determined. The DrBCAT monomer, comprising 358 amino acids, contains large and small domains connected with an interdomain loop. The cofactor PLP is located at the bottom of the active site pocket between two domains and near the dimer interface. The substrate (L-glutamate or KIC) is bound with key residues through interactions of the hydrogen bond and the salt bridge near PLP inside the active site pocket. Mutations of some interaction residues, such as Tyr71, Arg145, and Lys202, result in loss of the specific activity of the enzymes. In the interdomain loop, a dynamic loop (Gly173 to Gly179) clearly exhibits open and close conformations in structures of DrBCAT without and with substrates, respectively. DrBCAT shows the highest specific activity both in nature and under ionizing radiation, but with lower thermal stability above 60oC, than either BCAT from Escherichia coli (eBCAT) or from Thermus thermophilus (HB8BCAT). The dimeric molecular packing and the distribution of cysteine residues at the active site and the molecular surface might explain the resistance to radiation but small thermal stability of DrBCAT.
原文英語
頁(從 - 到)6206-6216
頁數11
期刊Journal of Bacteriology
194
發行號22
DOIs
出版狀態已發佈 - 十一月 1 2012
對外發佈

ASJC Scopus subject areas

  • 微生物學
  • 分子生物學

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