Attack of carboxymethylcellulose at opposite ends by two cellobiohydrolases from Cellulomonas fimi

The patterns of reducing sugar release following sequential addition of two Cellulomonas fimi cellobiohydrolases to carboxymethylcellulose corroborate previous evidence for preferential attack of β-1,4-glucans at opposite ends. In other experiments, sequential additions involving a single cellobiohydrolase and an Agrobacterium β-glucosidase indicate that CbhA attacks preferentially from the non-reducing end, CbhB from the reducing end. We suggest that all aerobic bacteria and fungi involved in cellulose hydrolysis produce a similar pair of cellobiohydrolases: a family 6 cellobiohydrolase that attacks from the non-reducing end and a family 48 (bacterial) or family 7 (fungal) cellobiohydrolase that attacks from the reducing end.