Cellobiohydrolase I (CBH I) was isolated from
a cellulolytic fungal strain Trichoderma pseudokoningii S38,
and its ultrastructure was investigated with a scanning tunneling
microscope (STM). The STM images showed that the
shape of intact CBH I was tadpole-like, consisting of a big
head and a long tail. It could be deduced that the head domain
was the core protein for the catalytic function, and the long
tail was the cellulose binding domain for substrate binding.
Thus, for this enzyme molecule, functional differentiation is
reflected in the structure peculiarities. This is the first direct
observation of the three-dimensional structure of intact CBH
I from real space at nanometer scale. The functional mechanism
is also discussed.