Permanent URL to this publication: http://dx.doi.org/10.5167/uzh-24624
Raschle, T; Arigoni, D; Brunisholz, R; Rechsteiner, H; Amrhein, N; Fitzpatrick, T B (2007). Reaction mechanism of pyridoxal 5'-phosphate synthase: detection of an enzyme-bound chromophoric intermediate. Journal of Biological Chemistry, 282(9):6098-6105.
Vitamin B6 is an essential metabolite in all organisms. De novo synthesis of the vitamin can occur through either of two mutually exclusive pathways referred to as deoxyxylulose 5-phosphate-dependent and deoxyxylulose 5-phosphate-independent. The latter pathway has only recently been discovered and is distinguished by the presence of two genes, Pdx1 and Pdx2, encoding the synthase and glutaminase subunit of PLP synthase, respectively. In the presence of ammonia, the synthase alone displays an exceptional polymorphic synthetic ability in carrying out a complex set of reactions, including pentose and triose isomerization, imine formation, ammonia addition, aldol-type condensation, cyclization, and aromatization, that convert C3 and C5 precursors into the cofactor B6 vitamer, pyridoxal 5'-phosphate. Here, employing the Bacillus subtilis proteins, we demonstrate key features along the catalytic path. We show that ribose 5-phosphate is the preferred C5 substrate and provide unequivocal evidence that the pent(ul)ose phosphate imine occurs at lysine 81 rather than lysine 149 as previously postulated. While this study was under review, corroborative crystallographic evidence has been provided for imine formation with the corresponding lysine group in the enzyme from Thermotoga maritima (Zein, F., Zhang, Y., Kang, Y.-N., Burns, K., Begley, T. P., and Ealick, S. E. (2006) Biochemistry 45, 14609-14620). We have detected an unanticipated covalent reaction intermediate that occurs subsequent to imine formation and is dependent on the presence of Pdx2 and glutamine. This step most likely primes the enzyme for acceptance of the triose sugar, ultimately leading to formation of the pyridine ring. Two alternative structures are proposed for the chromophoric intermediate, both of which require substantial modifications of the proposed mechanism.
|Item Type:||Journal Article, refereed, original work|
|Communities & Collections:||04 Faculty of Medicine > Functional Genomics Center Zurich|
08 University Research Priority Programs > Systems Biology / Functional Genomics
|DDC:||570 Life sciences; biology|
610 Medicine & health
|Date:||02 March 2007|
|Deposited On:||18 Dec 2009 14:12|
|Last Modified:||23 Nov 2012 13:28|
|Publisher:||American Society for Biochemistry and Molecular Biology|
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