When using head-derived fluids, we observed a single 45-kDa
cellulase activity band in our zymograms with purified fractions
(Fig. 3F). However, when staining this purified sample for total
protein before cutting the bands, we observed two protein bands of
45- and 43-kDa in the region of cellulase activity. It is likely that
overlapping activities explain the single activity signature observed
on zymograms. Proteins corresponding to each activity were
extracted from the PVDF blot and submitted to N-terminal sequencing
(Table 1). In database searches, the N-terminal sequence tag obtained
for the 45-kDa protein (AKYDYADAIRKSILFYQAQRS) had 84% identity
to the predicted N-terminal region of a cellulase from the digestive
system of the emma cricket, T. emma (Kim et al., 2008). A lower
probability and identity (70%) match was found to a predicted
cellulase from the acorn worm, Saccoglossus kowalevskii, and the Nterminal
region of a β-1,4-endoglucanase from the fresh water snail
Biomphalaria glabrata. From the 43-kDa purified cellulase, we
obtained a sequence tag (YEYRDALCKSLLF) that matched with low
probability and 76% identity to the N-terminal region of a cellulosebinding
protein from Eubacterium celulosolvens. Lower identity was
found for an endoglucanase from Ricinus communis (Table 1), and
other plant and insect-derived cellulases (data not shown).