The invention relates to an endocellulase catalytic domain comprising the sequence of SEQ ID NO: 1 or a functionally equivalent variant of said catalytic domain that substantially maintains or improves its catalytic activity. The invention also relates to a polypeptide, a nucleic acid, an expression cassette, a vector or a host cell. Additionally, the invention relates to the use of an endocellulase catalytic domain or the polypeptide of the invention for hydrolysing cellulose, producing bioethanol or as a detergent. The invention also relates to a method for hydrolysing cellulose and for producing bioethanol.