S-Ribosylhomocysteinase (LuxS) Is a Mononuclear Iron Protein

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• 作者：Jinge Zhu ; Eric Dizin ; Xubo Hu ; Anne-Sophie Wavreille ; Junguk Park ; and Dehua Pei
• 刊名：Biochemistry
• 出版年：2003
• 出版时间：April 29, 2003
• 年：2003
• 卷：42
• 期：16
• 页码：4717 - 4726
• 全文大小：199K
• 年卷期：v.42,no.16(April 29, 2003)
• ISSN：1520-4995

文摘

S-Ribosylhomocysteinase (LuxS) catalyzes the cleavage of the thioether linkage of S-ribosylhomocysteine (SRH) to produce L-homocysteine and 4,5-dihydroxy-2,3-pentanedione (DHPD). Thisis a key step in the biosynthetic pathway of the type II autoinducer (AI-2) in both Gram-positive andGram-negative bacteria. Previous studies demonstrated that LuxS contains a divalent metal cofactor, whichhas been proposed to be a Zn²⁺ ion. To gain insight into the catalytic mechanism of this unusual reactionand the function of the metal cofactor, we developed an efficient expression and purification system toproduce LuxS enriched in either Fe²⁺, Co²⁺, or Zn²⁺. Comparison of the catalytic properties and stabilityof the metal-substituted LuxS with those of the native enzyme revealed that the native metal ion is Fe²⁺.The electronic absorption spectrum of the Co(II)-substituted LuxS underwent dramatic catalysis-dependentchanges, suggesting the direct involvement of the metal ion in catalysis. Site-directed mutagenesis studiesshowed that Glu-57 and Cys-84 are essential for catalysis, most likely acting as general acids/bases. Reactionin D₂O resulted in the incorporation of deuterium at the C-1, C-2, and C-5 positions of the diketoneproduct. These data suggest a catalytic mechanism in which the metal ion catalyzes an intramolecularredox reaction, shifting the carbonyl group from the C-1 position to the C-3 position of the ribose.Subsequent mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-elimination at the C-4 and C-5 positions releases homocysteine as a free thiol.