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![[Figure 10]](ji5027fig10mag.jpg)
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Figure 10
The proposed catalytic mechanism of the alkaline α-galactosidase AtAkαGal3. Schematic presentation of the proposed catalytic mechanism of the alkaline α-galactosidase AtAkαGal3 with raffinose as a donor and an acceptor. The main interactions of residues involved in substrate recognition and the catalytic process are shown: the nucleophile (Asp383), acid/base catalyst (Asp447), Lys381 and Arg443 for the −1 subsite, Trp78, Lys75, Asp446 and Tyr449 for the +1 subsite, Lys75, Trp77, Thr342 and Asp346 for sucrose at the secondary product-binding site, Asp346 for the +3 subsite and water molecules that help to stabilize the +2 subsite. (a) Raffinose as a donor substrate binds in the catalytic binding site. (b) After the glycosidic bond of raffinose has been cleaved, the sucrose product rotates 180° and binds to the secondary product-binding site. The sucrose is subsequently released and galactose remains in the catalytic pocket. (c) Another raffinose, which acts as an acceptor substrate, enters the pocket and moves towards the galactose that remains at the −1 subsite. (d) The acceptor raffinose is engaged with galactose, resulting in the production of stachyose. |
![[Figure 10]](ji5027fig10.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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