Purification and characterization of a novel thermoacidophilic and thermostable alpha -mannosidase from the digestive fluid of oil palm weevil Rhynchophorus palmarum (Coleoptera: Curculionidae) larvae

An extracellular [alpha]-mannosidase with unusual properties was purified from the digestive fluid of oil palm weevil (Rhynchophorus palmarum Linnaeus) larvae using ammonium sulphate saturation, size exclusion and anion-exchange chromatography. The enzyme named RpltM is thermoacidophilic, thermostable and behaves like lysosomal [alpha]-mannosidase (EC 3.2.1.24). The molecular weight, Km value, optimum reaction temperature and pH are 108-112 kDa, 0.36 mM, 65[degree]C and 4.5, respectively. Zn2+ enhanced whereas Cu2+ Sodium dodecyl sulphate, swainsonine and 1,4-dideoxy-1,4-iminomannitol strongly inhibited its hydrolytic activity. The enzyme was stable for 25 min at 65[degree]C and retained 70% of its initial activity after 60 min. At 70[degree]C, around 60% of this activity was conserved after 25 min. RpltM retained more than 90% of its activity over a pH range of 4.2 to 5.0 and remained fully active in the presence of detergents such as nonidet P-40, triton X-100, polyoxyethylen-10-oleyl ether (up to 1%, w/v), dithiothreitol and [beta]-mercaptoethanol. The stability under these conditions is also better than that reported for other insect [alpha]-mannosidases. Thus, RpltM could be used as an important bioindustrial tool for removing mannose residues from oligosaccharides.