5-22: Aspartic Protease from Trichoderma reesei: Crystal structure and Statistical Coupling Analysis

Trichoderma reesei is an industrially important cellulolytic filamentous fungus, capable of secreting large amounts of several cellulose-degrading enzymes, which has been extensively studied with the aim to produce low-cost enzymes for the conversion of plant biomass materials into industrially useful bioproducts, such as sugars and bioethanol. Fungal aspartic proteases have been shown to participate in the processing of secreted enzymes and, as a rule, to act as regulatory enzymes. Here we present crystal structures of an aspartic protease from Trichoderma reesei (TrAsP) and its complex with a competitive inhibitor, pepstatin A, solved and refined at 1.85 Å resolution. The three-dimensional structure of TrAsP is folded in a predominantly β-sheet bilobal structure with the N-terminal and C-terminal domains of about the same size, that undergo a rigid body movement upon inhibitor binding, tightly enclosing the inhibitor. The structures of TrAsP were used as a template for performing statistical coupling analysis (SCA) of the aspartic protease family. This approach permitted, for the first time, identification of a network of structurally linked residues putatively mediating conformational changes relevant to the function of this family of enzymes. SCA reveals co-evolved continuous clusters of amino acid residues which extend from the active site into the hydrophobic cores of each of the two domains and also include amino acid residues from the flap regions, highlighting the importance of these parts of the protein for its enzymatic activity, extending our comprehension of the protease action and opening new possibilities for its modulation.