1s0a: Difference between revisions

==Overview==

The vitamin B(6)-dependent enzyme 7,8-diaminopelargonic acid (DAPA), synthase catalyzes the antepenultimate step in the synthesis of biotin, the transfer of the alpha-amino group of S-adenosyl-l-methionine (SAM) to, 7-keto-8-aminopelargonic acid (KAPA) to form DAPA. The Y17F, Y144F, and, D147N mutations in the active site were constructed independently. The, k(max)/K(m)(app) values for the half-reaction with DAPA of the Y17F and, Y144F mutants are reduced by 1300- and 2900-fold, respectively, compared, to the WT enzyme. Crystallographic analyses of these mutants do not show, significant changes in the structure of the active site. The kinetic, deficiencies, together with a structural model of the enzyme-PLP/DAPA, Michaelis complex, point to a role of these two residues in recognition of, the DAPA/KAPA substrates and in catalysis. The k(max)/K(m)(app) values for, the half-reaction with SAM are similar to that of the WT enzyme, showing, that the two tyrosine residues are not involved in this half-reaction., Mutations of the conserved Arg253 uniquely affect the SAM kinetics, thus, establishing this position as part of the SAM binding site. The D147N, mutant is catalytically inactive in both half-reactions. The structure of, this mutant exhibits significant changes in the active site, indicating, that this residue plays an important structural role. Of the four residues, examined, only Tyr144 and Arg253 are strictly conserved in the available, amino acid sequences of DAPA synthases. This enzyme thus provides an, illustrative example that active site residues essential for catalysis are, not necessarily conserved, i.e., that during evolution alternative, solutions for efficient catalysis by the same enzyme arose. Decarboxylated, SAM [S-adenosyl-(5')-3-methylthiopropylamine] reacts nearly as well as SAM, and cannot be eliminated as a putative in vivo amino donor.

==About this Structure==

1S0A is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with NA as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Adenosylmethionine--8-amino-7-oxononanoate_transaminase Adenosylmethionine--8-amino-7-oxononanoate transaminase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.6.1.62 2.6.1.62] Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1S0A OCA].

 

==Reference==

Conserved and nonconserved residues in the substrate binding site of 7,8-diaminopelargonic acid synthase from Escherichia coli are essential for catalysis., Sandmark J, Eliot AC, Famm K, Schneider G, Kirsch JF, Biochemistry. 2004 Feb 10;43(5):1213-22. PMID:[http://ispc.weizmann.ac.il//pmbin/getpm?pmid=14756557 14756557]

[[Category: Single protein]]

[[Category: Eliot, A.C.]]

[[Category: Famm, K.]]

[[Category: Kirsch, J.F.]]

[[Category: Sandmark, J.]]

[[Category: Schneider, G.]]

[[Category: aminotransferase]]