Crystal structure of human muscle aldolase complexed with fructose 1,6-bisphosphate: Mechanistic implications

Fructose 1,6-bisphosphate aldolase catalyzes the reversible cleavage of fru ctose 1,6-bisphosphate and fructose 1-phosphate to dihydroxyacetone phospha te and either glyceraldehyde 3-phosphate or glyceraldehyde, respectively Ca talysis involves the formation of a Schiff's base intermediate formed at th e E-amino group of Lys229. The existing apo-enzyme structure was refined us ing the crystallographic free-R-factor and maximum likelihood methods that have been shown to give improved structural results that are less subject t o model bias. Crystals were also soaked with the natural substrate (fructos e 1,6-bisphosphate), and the crystal structure of this complex has been det ermined to 2.8 Angstrom. The apo structure differs from the previous Brookh aven-deposited structure (1 ald) in the flexible C-terninal region. This is also the region where the native and complex structures exhibit difference s. The conformational changes between native and complex structure rue not large, but the observed complex does not involve the full formation of the Schiff's base intermediate, and suggests a preliminary hydrogen-bonded Mich aelis complex before the formation of the covalent complex.