1O8G: Pectate Lyase C from Erwinia Chrysanthemi at pH 9.5 with 5mM Ca2+

Ca(2+) is essential for in vitro activity of Erwinia chrysanthemi pectate lyase C (PelC). Crystallographic analyses of 11 PelC-Ca(2+) complexes, formed at pH 4.5, 9.5, and 11.2 under varying Ca(2+) concentrations, have been solved and refined at a resolution of 2.2 A. The Ca(2+) site represents a new motif for Ca(2+), consisting primarily of beta-turns and beta-strands. The principal differences between PelC and the PelC-Ca(2+) structures at all pH values are the side-chain conformations of Asp-129 and Glu-166 as well as the occupancies of four water molecules. According to calculations of pK(a) values, the presence of Ca(2+) and associated structural changes lower the pK(a) of Arg-218, the amino acid responsible for proton abstraction during catalysis. The Ca(2+) affinity for PelC is weak, as the K(d) was estimated to be 0.132 (+/-0.004) mm at pH 9.5, 1.09 (+/-0.29) mm at pH 11.2, and 5.84 (+/-0.41) mm at pH 4.5 from x-ray diffraction studies and 0.133 (+/-0.045) mm at pH 9.5 from intrinsic tryptophan fluorescence measurements. Given the pH dependence of Ca(2+) affinity, PelC activity at pH 4.5 has been reexamined. At saturating Ca(2+) concentrations, PelC activity increases 10-fold at pH 4.5 but is less than 1% of maximal activity at pH 9.5. Taken together, the studies suggest that the primary Ca(2+) ion in PelC has multiple functions.
PDB ID: 1O8GDownload
MMDB ID: 21918
PDB Deposition Date: 2002/11/27
Updated in MMDB: 2012/10
Experimental Method:
x-ray diffraction
Resolution: 2.2  Å
Source Organism:
Similar Structures:
Biological Unit for 1O8G: monomeric; determined by author and by software (PQS)
Molecular Components in 1O8G
Label Count Molecule
Protein (1 molecule)
Pectate Lyase C
Molecule annotation
Chemical (1 molecule)
* Click molecule labels to explore molecular sequence information.

Citing MMDB