Premium
Influence of divalent cations on the structural thermostability and thermal inactivation kinetics of class II xylose isomerases
Author(s) -
Epting Kevin L.,
Vieille Claire,
Zeikus J. Gregory,
Kelly Robert M.
Publication year - 2005
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2005.04577.x
Subject(s) - thermostability , bacillus licheniformis , chemistry , kinetics , thermophile , mesophile , isomerase , crystallography , divalent , metal , stereochemistry , biochemistry , bacillus subtilis , bacteria , enzyme , biology , organic chemistry , physics , quantum mechanics , genetics
The effects of divalent metal cations on structural thermostability and the inactivation kinetics of homologous class II d ‐xylose isomerases (XI; EC 5.3.1.5) from mesophilic ( Escherichia coli and Bacillus licheniformis ), thermophilic ( Thermoanaerobacterium thermosulfurigenes ), and hyperthermophilic ( Thermotoga neapolitana ) bacteria were examined. Unlike the three less thermophilic XIs that were substantially structurally stabilized in the presence of Co 2+ or Mn 2+ (and Mg 2+ to a lesser extent), the melting temperature [( T m ) ≈100 °C] of T. neapolitana XI (TNXI) varied little in the presence or absence of a single type of metal. In the presence of any two of these metals, TNXI exhibited a second melting transition between 110 °C and 114 °C. TNXI kinetic inactivation, which was non‐first order, could be modeled as a two‐step sequential process. TNXI inactivation in the presence of 5 m m metal at 99–100 °C was slowest in the presence of Mn 2+ [half‐life ( t 1/2 ) of 84 min], compared to Co 2+ ( t 1/2 of 14 min) and Mg 2+ ( t 1/2 of 2 min). While adding Co 2+ to Mg 2+ increased TNXI's t 1/2 at 99–100 °C from 2 to 7.5 min, TNXI showed no significant activity at temperatures above the first melting transition. The results reported here suggest that, unlike the other class II XIs examined, single metals are required for TNXI activity, but are not essential for its structural thermostability. The structural form corresponding to the second melting transition of TNXI in the presence of two metals is not known, but likely results from cooperative interactions between dissimilar metals in the two metal binding sites.