X-ray structure of HEW lysozyme in complex with (NAG)₆. The protein is drawn in worm form colored in rainbow order from its N-terminus (blue) to its C-terminus (red) embedded in its transparent molecular surface (gray). The (NAG)₆, which is drawn in stick form with its sugar residues designated A, at its nonreducing end, through F, at its reducing end, binds in a deep cleft in the enzyme surface. Rings A, B, and C (colored according to atom type with C green, N blue, and O red) are observed in the X-ray structure of the complex of (NAG)₃ with lysozyme; the positions of rings D, E, and F (C cyan, N blue, O red) were inferred by model building. The side chains of lysozyme's active site residues, Glu 35 and Asp 52, which are drawn in space-filling form (C yellow, O red), catalyze the hydrolysis of the glycosidic bond between rings D and E. [Based on an X-ray structure by David Phillips, Oxford University. PDBid 1HEW.]