2Pushchino State University, pr. Nauki 3, 142290 Pushchino, Moscow Region, Russia; fax: (496) 732-711
* To whom correspondence should be addressed.
Received December 23, 2009; Revision received February 10, 2010
The gene fba from the thermotolerant obligate methanotroph Methylococcus capsulatus Bath was cloned and expressed in Escherichia coli BL21(DE3). The fructose-1,6-bisphosphate aldolase (FBA) carrying six His on the C-end was purified by affinity metal chelating chromatography. The Mc. capsulatus FBA is a hexameric enzyme (240 kDa) that is activated by Co2+ and inhibited by EDTA. The enzyme displays low Km to fructose-1,6-bisphosphate (FBP) and higher Km to the substrates of aldol condensation, dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. The FBA also catalyzes sedoheptulose-1,7-bisphosphate cleavage. The presence of Co2+ in the reaction mixture changes the kinetics of FBP hydrolysis and is accompanied by inhibition of the reaction by 2 mM FBP. Phylogenetically, the Mc. capsulatus enzyme belongs to the type B of class II FBAs showing high identity of translated amino acid sequence with FBAs from autotrophic bacteria. The role of the FBA in metabolism of Mc. capsulatus Bath, which realizes simultaneously three C1 assimilating pathways (the ribulose monophosphate, the ribulose bisphosphate, and the serine cycles), is discussed.
KEY WORDS: fructose-1,6-bisphosphate aldolase, methanotrophs, Methylococcus capsulatus, Calvin cycle