Characterization, cloning, and evolutionary history of the chloroplast andcytosolic class I aldolases of the red alga Galdieria sulphuraria

Two fructose-1,6-bisphosphate aldolases from the acido- and thermophilic re d alga Galdieria sulphuraria were purified to apparent homogeneity and N-te rminally microsequenced. Both aldolases had similar biochemical properties such as Km (FBP) (5.6-5.8 mu M) and molecular masses of the native enzymes (165 kDa) as determined by size exclusion chromatography. The subunit size of the purified aldolases, as determined by SDS-PAGE, was 42 kDa for both a ldolases. The isoenzymes were not inhibited by EDTA or affected by cysteine or potassium ions, implying that they belong to the class I group of aldol ases, while other red algae are known to have one class I and one class II aldolase inhibited by EDTA. cDNA clones of the cytosolic and plastidic aldo lases were isolated and sequenced. The gene for the cytosolic isoenzyme con tained a 303 bp untranslated leader sequence, while the gene for the plasti dic isoenzyme exhibited a transit sequence of 56 amino-acid residues. Both isoenzymes showed about 48% homology in the deduced amino-acid sequences. A gene tree relates both aldolases to the basis of early eukaryotic class I aldolases. The phylogenetic relationship to other aldolases, particularly t o cyanobacterial class II aldolases, is discussed. (C) 1999 Elsevier Scienc e B.V. All rights reserved.