b) MHETase is believed to use a catalytic triad to hydrolyze the ester linkage in MHET, just

like the catalytic triad in the serine proteases. Examine the structure of MHETase

complexed with the analog and identify the 3 residues in the catalytic triad. For each

one, find the most important distance between that residue and its partner in the

mechanism and fill out the chart, identifying the 2 atoms used and the distance between

them. Also identify the secondary structure in which it is found (e.g., a-helix, ß-strand,

tight turn, or loop).

Residue

(name & #)

Ser

His

Asp

Identify the most relevant inter-atomic distance

and identify the atom name (click on it in PyMOL)

(e.g., "CB" or "C4" or "OG")

Atom in Ser:

Atom in substrate analog:

Atom in His:

Atom in Ser:

Atom in Asp:

Atom in His:

distance

between

atoms (Å)

2°

structural

context/nWhat other residues in the enzyme are important for binding MHET? Identify at least 4

that seem to play an important role.

Residue

(chain,

name & #)

Atom of the residue and the substrate analog? distance

Type(s) of interaction (e.g., H-bond,

between

charge-charge, coordination bond, van der Waals)

atoms (Å)

2⁰

structural

context

Which, if any, of these residues might explain why MHET is a good substrate, but BHET

is not? And how would it explain the substrate specificity?