l -Arabinose Isomerase Formation in a Conditional Mutant of Gene araA of Escherichia coli B/r

Abstract

A temperature-sensitive mutant of Escherichia coli in which the synthesis of l -arabinose isomerase is blocked during growth at 42 C was found to possess the following properties. (i) The mutation occurred in the structural gene for the isomerase, gene araA . (ii) During growth at elevated temperatures the mutant accumulates a product which is a precursor to the active enzyme. (iii) The precursor produced at 42 C is slowly converted to active enzyme at 28 C in the absence of protein and ribonucleic acid synthesis. It is concluded that the mutation results in a change in the structure of isomerase which causes formation of active enzyme to be thermolabile at a step beyond the level of translation.

Crystallization and preliminary X-ray crystallographic analysis ofL-arabinose isomerase from thermophilicGeobacillus kaustophilus

“…The asymmetric unit is likely to contain six GKAI molecules, corresponding to a calculated Matthews coefficient of 2.25 Å 3 Da À1 and a solvent content of 45.39% (Matthews, 1968). Previously, biophysical and electronmicroscopy studies demonstrated that native ECAI exists as a homohexamer complex in solution (Pauley et al, 1972;Wallace et al, 1978), while thermostable AIs mostly exhibit homotetramers as described in Lee et al (2004), Jørgensen et al (2004) and Manjasetty & Chance (2006). However, our analytical size-exclusion chromatography revealed that the purified GKAI in this study has a hexameric structure ($321 kDa), which correlated well with the predicted molecular weight ($336 kDa) of the homohexameric complex.…”