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The molecular structure of two homogeneously purified cellobiohydrolases
from Trichoderma reesei has been studied employing high resolution
transmission electron microscopy (TEM) and digital image processing. By
combining low dose TEM, a 3% (w/v) solution of methylamine tungstate as
the negative staining agent, and digital image processing, it has been
possible to unambiguously view molecular architecture of cellobiohydrolases
from Trichoderma reesei. Cellobiohydrolase I(CBH I) and Cellobiohydrolase
II (CBH II) have ellipsoidal heads and long, extended helical tails. CBH
I has a head with an average diameter of 4.5 - 0.5 nm. The average length
of CBH I is 15.1+- 1.3 nm. CBH II has a head with an average diameter of
4.4 - 0.3 nm. Average length of CBH I is 13.4+- 2.6 nm. Overall, the structure
of the digitally enhanced TEM images of these two glycosyl hydrolases correlated
well with the reported small angle X-ray scattering analysis (SAXS) models,
thereby establishing the reliability of high resolution TEM studies in
a novel way. The linker regions (LRs) of two CBHs have been visualized.
The LR of both enzymes are probably helical in nature, suggesting an extended
peptide sequence that lacks secondary structure due to the lack of amino
acid/amino acid interactions in this region. A possible structural and
functional role of O-glycosylation on these linker regions is given by
combining the TEM observations with known biochemical data
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Last modified March 25, 2008.
This document is maintained by R.
Malcolm Brown, Jr.