The dhnA gene of Escherichia coli encodes a Class I fructose bisphosphate aldolase

Abstract

The gene encoding the Escherichia coli Class I fructose-1,6-bisphosphate aldolase (FBP aldolase) has been cloned and the protein overproduced in high amounts. This gene sequence has previously been identified as encoding an E. coli dehydrin in the GenBank™ database [gene dhnA; entry code U73760; Close and Choi (1996) Submission to GenBank™]. However, the purified protein overproduced from the dhnA gene shares all its properties with those known for the E. coli Class I FBP aldolase. The protein is an 8–10-mer with a native molecular mass of approx. 340 kDa, each subunit consisting of 349 amino acids. The Class I enzyme shows low sequence identity with other known FBP aldolases, both Class I and Class II (in the order of 20%), which may be reflected by some novel properties of this FBP aldolase. The active-site peptide has been isolated and the Schiff-base-forming lysine residue (Lys236) has been identified by a combination of site-directed mutagenesis, kinetics and electrospray-ionization MS. A second lysine residue (Lys238) has been implicated in substrate binding. The cloning of this gene and the high levels of overexpression obtained will facilitate future structure–function studies.