1ux0

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spinqualitylabelsall models 1ux0, resolution 1.99Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

BACILLUS SUBTILIS CYTIDINE DEAMINASE WITH AN ARG56- GLN SUBSTITUTION

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, 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

1UX0 is a Single protein structure of sequence from Bacillus subtilis with ZN and THU as ligands. Active as Cytidine deaminase, with EC number 3.5.4.5 Structure known Active Site: AC1. Full crystallographic information is available from OCA.

Reference

Structural, kinetic, and mutational studies of the zinc ion environment in tetrameric cytidine deaminase., Johansson E, Neuhard J, Willemoes M, Larsen S, Biochemistry. 2004 May 25;43(20):6020-9. PMID:15147186

Page seeded by OCA on Mon Nov 5 17:14:16 2007