IE-CBHI or Cellobiohydrolase I is a plant-produced exocellulase (Cel6A; E.C. from Hypocrea jecorina. It is an enzyme present in many fungi, but particularly wood rot fungi. It is a monomer of 53 kDa with a catalytic domain and a cellulose binding domain. Its reaction adds water to the glucose bonds in cellulose (non-reducing ends of the chain), yielding cellobiose.