In agarolytic microorganisms, a-neoagarobiose hydrolase (NABH) is an essential enzyme to metabolize
agar because it converts α-neoagarobiose (O-3,6-anhydro-alpha-L-galactopyranosyl-(1,3)-D-galactose)
into fermentable monosaccharides (D-galactose and 3,6-anhydro-L-galactose) in the agarolytic pathway.
NABH can be divided into two biological classes by its cellular location. Here, we describe a structure and
function of cytosolic NABH from Saccharophagus degradans 2–40 in a native protein and D-galactose complex
determined at 2.0 and 1.55 Å, respectively. The overall fold is organized in an N-terminal helical
extension and a C-terminal five-bladed β-propeller catalytic domain. The structure of the enzyme–ligand
(D-galactose) complex predicts a +1 subsite in the substrate binding pocket. The structural features may
provide insights for the evolution and classification of NABH in agarolytic pathways
