3.2.1.123 by vapor diffusion method, crystals of the native enzyme belong to space group P21 with unit cell dimensions a=53.8 A, b=92.9 Å, c=94.5 A,beta=98.6°, to 1.6 A resolution. Crystal structure of mutant E351S in complex with the ganglioside GM3, crystals belong to space group C2, with unit cell dimensions a = 77.8 A, b = 62.0 A, c = 102.8 A, beta = 112.3°, to 1.1 A resolution. Active site of endo-glycoceramidase is split into a wide, polar cavity to bind the polyhydroxylated oligosaccharide moiety and a narrow, hydrophobic tunnel to bind the ceramide lipid chains 680770 3.2.1.123 EGC-inhibitor complexes, to 1.50-1.85 A resolution. Both (3R,4R,5R)-4-(beta-D-glucopyranosyl)oxy-3-hydroxy-5-(hydroxymethyl)piperidine and (5R,6R,7S,8S)-6-(beta-D-glucopyranosyloxy)-5,6,7,8-tetrahydro-5-(hydroxymethyl)imidazo-[1,2-a]pyridine-7,8-diol bind in the -2 and -1 subsites of the enzyme, with the isofagomine and glucoimidazole moieties located in the catalytic -1 subsite. 1-(4-dimethylamino)benzoylamino-1,2,5-trideoxy-2,5-imino-d-mannitol binds in the -1 subsite in an envelope conformation. The ring nitrogen superimposes with the anomeric carbon of the lactosyl-enzyme intermediate and the ring nitrogen of the isofagomine 677557 3.2.1.123 hanging drop vapor diffusion method at 20°C, X-ray crystal structures of the enzyme alone and in complex with its substrates monosialodihexosylganglioside and monosialotetrahexosylganglioside determined at 2.11 A resolution. Compared with EGCase II from Rhodococcus sp. M-777, which possesses strict substrate specificity, EGCase I from Rhodococcus hoagii 103S possesses a longer alpha7-helix and a shorter loop 4, which forms a larger substrate-binding pocket that could accommodate more extended oligosaccharides. In addition, loop 2 and loop 8 of the enzyme adopt a more open conformation, which also enlarges the oligosaccharide-binding cavity 751102