Several recombinant fungal enzymes (endoglucanase and pectinase) were studied 
for their interactions with alpha-expansin in cell wall extension and 
polysaccharide degradation. Both Cel12A and Cel5A were able to hydrolyze 
cellulose CMC-Na and mixed-linkage beta-glucan. In contrast to Cel5A, Cel12A 
could also hydrolyze xyloglucan and induce wall extension of cucumber hypocotyls 
in an in vitro assay. Combining alpha-expansin, even at high concentrations, 
with Cel12A did not enhance the maximum/final wall extension rate induced by 
Cel12A alone. These results strongly suggest that modification/degradation of 
the xyloglucan molecule/network is the key for cell wall extension, and 
alpha-expansin and Cel12A may share the same acting site in the substrate. 
Pectinase (Pel1, a pectin lyase) enhanced alpha-expansin-induced wall extension 
in a concentration-dependent manner, suggesting that the pectin network may 
normally regulate accessibility of expansin to the xyloglucan-cellulose complex. 
alpha-Expansin enhanced Cel12A's hydrolytic activity on cellulose CMC-Na but not 
on xyloglucan and beta-glucan. Expansin did not affect Cel5A's hydrolytic 
activity. Interestingly, expansin also enhanced Pel1's activity on degrading 
high esterified pectin. A potential explanation for why expansin could 
synergistically interact with only certain enzymes on specific polysaccharides 
is discussed. Additional results also suggested that cell wall swelling may not 
be a significant event during the action of expansin and hydrolases.