Digestion of single crystals of mannan I by an endo-mannanase from Trichoderma reesei

The enzymatic degradation of single crystals of mannan I with the catalytic core domain of a beta-mannanase (EC 3.2.1.78 or Man5A) from Trichoderma re esei was investigated by transmission electron microscopy and electron diff raction. The enzyme attack took place at the edge of the crystals and progr essed towards their centres. Quite remarkably the crystalline integrity of the crystals was preserved almost to the end of the digestion process. This behaviour is consistent with an endo-mechanism, where the enzyme interacts with the accessible mannan chains located at the crystal periphery and cle aves one mannan molecule at a time. The endo mode of digestion of the cryst als was confirmed by an analysis of the soluble degradation products.