The X-ray structure of hen egg white (HEW) lysozyme

(a) The polypeptide chain is show with a bound (NAG)6 substrate (green). The positions of the backbone Ca atoms are indicated together with the side chains of the catalytic residues Asp 52 and Glu 35 (red) and those that form disulfide bonds (yellow). The substrate’s sugar rings are designated A, at its nonreducing end (right), through F, at its reducing end (left). Lysozyme catalyzes the hydrolysis of the glycosidic bond between residues D and E. Rings A, B, and C are observed in the X-ray structure of the complex of (NAG)3 with lysozyme; the positions of rings D, E, and F were inferred from model building studies.

 

(b) A ribbon diagram of lysozyme highlighting the protein’s secondary structure and indicating the positions of its catalytically important side chains.

(c) A computer-generated model showing the protein’s molecular envelope (purple) and Ca backbone (blue). The side chains of the catalytic residues, Asp 52 (above) and Glu 35 (below), are colored yellow. Note the enzyme’s prominent substrate-binding cleft.