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PDBsum entry 1lzv

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Lyase PDB id
1lzv
Jmol
Contents
Protein chain
256 a.a. *
Metals
_ZN
Waters ×56
* Residue conservation analysis

References listed in PDB file
Key reference
Title Kinetic analysis of multiple proton shuttles in the active site of human carbonic anhydrase.
Authors C.Tu, M.Qian, H.An, N.R.Wadhwa, D.Duda, C.Yoshioka, Y.Pathak, R.Mckenna, P.J.Laipis, D.N.Silverman.
Ref. J Biol Chem, 2002, 277, 38870-38876. [DOI no: 10.1074/jbc.M205791200]
PubMed id 12171926
Abstract
We have prepared a site-specific mutant of human carbonic anhydrase (HCA) II with histidine residues at positions 7 and 64 in the active site cavity. Using a different isozyme, we have placed histidine residues in HCA III at positions 64 and 67 and in another mutant at positions 64 and 7. Each of these histidine residues can act as a proton transfer group in catalysis when it is the only nonliganding histidine in the active site cavity, except His(7) in HCA III. Using an (18)O exchange method to measure rate constants for intramolecular proton transfer, we have found that inserting two histidine residues into the active site cavity of either isozyme II or III of carbonic anhydrase results in rates of proton transfer to the zinc-bound hydroxide that are antagonistic or suppressive with respect to the corresponding single mutants. The crystal structure of Y7H HCA II, which contains both His(7) and His(64) within the active site cavity, shows the conformation of the side chain of His(64) moved from its position in the wild type and hydrogen-bonded through an intervening water molecule with the side chain of His(7). This suggests a cause of decreased proton transfer in catalysis.
Figure 1.
Fig. 1. The pH dependence of R[H2O]/[E] (s 1) catalyzed by wild type HCA II ( ), Y7H HCA II ( ), Y7H/H64A HCA II ( circle ), and H64A HCA II ( ). The values were determined by 18O exchange at 25 °C using solutions containing no buffers; ionic strength of solution was maintained at 0.2 M by addition of Na[2]SO[4]. The lines are least squares fits of Equation 6 to the data yielding the values of pK[a] of the donor and acceptor groups and the values of k[B] given in Table III. The data for H64A HCA II is from Qian et al. (30).
Figure 3.
Fig. 3. The pH dependence of R[H2O]/[E] (ms 1) catalyzed by wild type HCA III ( ), K64H HCA III ( ), R67H HCA III ( ), and the double mutant K64H/R67H HCA III ( circle ). The values were determined by 18O exchange at 25 °C using solutions containing no buffers; ionic strength of solution was maintained at 0.2 M by addition of Na[2]SO[4]. The lines are least squares fits of Equation 6 to the data yielding the values of pK[a] of the donor and acceptor groups and the values of k[B] given in Table IV.
The above figures are reprinted by permission from the ASBMB: J Biol Chem (2002, 277, 38870-38876) copyright 2002.
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