1ux1: Difference between revisions
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==Overview== | ==Overview== | ||
The zinc-containing cytidine deaminase (CDA, EC 3.5.4.5) is a pyrimidine, salvage enzyme catalyzing the hydrolytic deamination of cytidine and, 2'-deoxycytidine forming uridine and 2'-deoxyuridine, respectively., Homodimeric CDA (D-CDA) and homotetrameric CDA (T-CDA) both contain one, zinc ion per subunit coordinated to the catalytic water molecule. The zinc, ligands in D-CDA are one histidine and two cysteine residues, whereas in, T-CDA zinc is coordinated to three cysteines. Two of the zinc coordinating, cysteines in T-CDA form hydrogen bonds to the conserved residue Arg56, and, this residue together with the dipole moments from two alpha-helices, partially neutralizes the additional negative charge in the active site, leading to a catalytic activity similar to D-CDA. Arg56 has been, .. | The zinc-containing cytidine deaminase (CDA, EC 3.5.4.5) is a pyrimidine, salvage enzyme catalyzing the hydrolytic deamination of cytidine and, 2'-deoxycytidine forming uridine and 2'-deoxyuridine, respectively., Homodimeric CDA (D-CDA) and homotetrameric CDA (T-CDA) both contain one, zinc ion per subunit coordinated to the catalytic water molecule. The zinc, ligands in D-CDA are one histidine and two cysteine residues, whereas in, T-CDA zinc is coordinated to three cysteines. Two of the zinc coordinating, cysteines in T-CDA form hydrogen bonds to the conserved residue Arg56, and, this residue together with the dipole moments from two alpha-helices, partially neutralizes the additional negative charge in the active site, leading to a catalytic activity similar to D-CDA. Arg56 has been, substituted by a glutamine (R56Q), the corresponding residue in D-CDA, an, alanine (R56A), and an aspartate (R56D). Moreover, one of the, zinc-liganding cysteines has been substituted by histidine to mimic D-CDA, alone (C53H) and in combination with R56Q (C53H/R56Q). R56A, R56Q, and, C53H/R56Q contain the same amount of zinc as the wild-type enzyme. The, zinc-binding capacity of R56D is reduced. Only R56A, R56Q, and C53H/R56Q, yielded measurable CDA activity, R56A and R56Q with similar K(m) but, decreased V(max) values compared to wild-type enzyme. Because of, dissociation into its inactive subunits, it was impossible to determine, the kinetic parameters for C53H/R56Q. R56A and C53H/R56Q display increased, apparent pK(a) values compared to the wild-type enzyme and R56Q. On the, basis of the structures of R56A, R56Q, and C53H/R56Q an explanation is, provided of kinetic results and the apparent instability of C53H/R56Q. | ||
==About this Structure== | ==About this Structure== | ||
1UX1 is a | 1UX1 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Bacillus_subtilis Bacillus subtilis] with ZN, THU and TRS as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Cytidine_deaminase Cytidine deaminase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.5.4.5 3.5.4.5] Structure known Active Site: AC1. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1UX1 OCA]. | ||
==Reference== | ==Reference== | ||
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[[Category: zinc binding]] | [[Category: zinc binding]] | ||
''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on | ''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on Mon Nov 5 14:34:48 2007'' | ||
