Fructose 6-Phosphate Aldolase FSA

The tight packing of FSA may explain its unusual thermostability (50% of activity retained after 16 h at 75 °C) [36, 37]. 

A schematic representation of the active sites of transaldolase B is given in Fig. 

together with the corresponding amino acid residues in the other Class I aldolases, fructose 1,6-bisphosphate, and FSA. There is one amino acid residue in the active site of FSA which has no counterpart in TAL B, Tyr-131. 

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Figure 10.14 Natural glycolytic substrates of the fructose 1,6-bisphosphate aldolase (FruA) and fructose 6-phosphate aldolase (FSA).

Functionally related to FruA is the novel class I fructose 6-phosphate aldolase (FSA) from E. coli, which catalyzes the reversible cleavage of fructose 6-phosphate (30) to give dihydroxyacetone (31) and d-(18) [90]. It is the only known enzyme that does not require the expensive phosphorylated nucleophile DHAP for synthetic purpose. 

Although fructose-6-phosphate aldolase (FSA) does not belong to the DHAP-dependent aldolases group, it deserves to be mentioned in this chapter as it can be considered as an alternative to those enzymes, or at least, an alternative to FBPA. FSA was described for the first time by Schiirmann and Sprenger in E. coli K-12 strain MG1655 [50]. The enzyme is a class I aldolase with a homodecameric... 

Fig. 2.2.2.S Three-dimensional structures of transaldolase B (TAL B) and fructose 6-phosphate aldolase (FSA) from E. coli. a) TAL B forms a dimer structure b), c) FSA is a decameric enzyme consisting of two pentamer rings (right) one on top of the other, b) Two adjacent subunits of FSA showing the C-terminal extension of one...

Pig. 6.5.13 d-Fructose-6-phosphate aldolase (FSA) catalyzed aldol additions of DHA to a number of aldehyde acceptors... 

The (3S,4R) configured probes were prepared by enzymatic routes based on the stereospecific formation of a C-C bond catalyzed by either TK with Li-HPA as donor or by fructose-6-phosphate aldolase (FSA) Ref. [41]. The advantage of FSA for the synthesis of these probes is that acceptor substrates were commercially available, whereas a-hydroxylated TK acceptor substrates had to be prepared first by chemical routes [40, 41]. In particularly, the recently engineered FSA(A129S) variant that was optimized for dihydroxyacetone (DHA) as the donor substrate was found to be a powerful biocatalyst, leading to D-ketose analogs 16a and 16b with 67% and 77% yields, respectively. TK reactions furnished the same products but with lower yields only (37% and 47% respectively) (Scheme 15.17). 

DIHYDROXYACETONE PHOSPHATE (DHAP)-DEPENDENT ALDOLASES, d-FRUCTOSE-6-PHOSPHATE ALDOLASE (FSA) AND TRANSALDOLASES... 

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