A Novel Enzyme, {lambda}-Carrageenase, Isolated from a Deep-Sea Bacterium

A λ-carrageenan–degrading Pseudoalteromonas bacterium, strain CL19, was isolated from a deep-sea sediment sample. A λ-carrageenase from the isolate was purified to homogeneity from cultures containing λ-carrageenan as a carbon source. This is the first report of the isolation of λ-carrageenase together with the gene sequence for the enzyme. The molecular mass of the purified enzyme was approximately 100 kDa on both SDS-PAGE and gel-filtration chromatography, suggesting that the enzyme is a monomer. The optimal pH and temperature for activity were about 7 and 35°C, respectively. The enzyme had specific activity of 253 U/mg protein. The enzyme required monovalent salts for the activity. Carbohydrates, such as sorbitol, sucrose, trehalose, improved the enzyme stability. The pattern of λ-carrageenan hydrolysis showed that the enzyme is an endo-type λ-carrageenase, and the final main product was a tetrasaccharide of the λ-carrageenan ideal structure with galactose 2,6-disulfate at the reducing end, indicating the enzyme cleaves the β-1,4 linkages of its backbone structure. Furthermore, the gene ( cglA ) encoding the enzyme was sequenced. It encoded a mature protein of 103 kDa (917 amino acids). Remarkably, the deduced amino acid sequence showed no similarity to any reported proteins.