Catalysis by a rigid enzyme

Many enzymes are dynamic entities, sampling conformational states that are relevant for catalytic activity. Nevertheless, crystal structures of catalytic intermediates suggest that other enzymes do not require structural changes for activity. The single domain enzyme xylanase from Bacillus circulans (BCX) is involved in the degradation of hemicellulose. It is demonstrated that BCX in solution is undergoing minimal structural changes during catalysis. A rigid protein matrix provides a frame for fast substrate binding, followed slow distortion induced by the enzyme to enable hydrolysis. Thus, the dynamics of the substrate rather than the enzyme are essential for catalysis.