Crystal structure and biochemical characterization of CJP38, a β-1,3-glucanase and allergen of Cryptomeria japonica pollen

A 38 kDa β-1,3-glucanase allergen from Cryptomeria japonica pollen (CJP38) was recombinantly produced in E. coli and purified to homogeneity with the use of Ni-affinity resin. CJP38 hydrolyzed β-1,3-glucans such as CM-curdlan and laminarioligosaccharides in an endo-splitting manner. The optimum pH and temperature for β-1,3-glucanase activity were approximately 4.5 and 50 °C, respectively. The enzyme was stable at 30–60 °C and pH 4.0–10.5. Furthermore, CJP38 catalyzed a transglycosylation reaction to yield reaction products with a molecular weight higher than those of the starting laminarioligosaccharide substrates. The three-dimensional structure of CJP38 was determined using X-ray crystallography at 1.5 Å resolution. CJP38 exhibited the typical (β/α)₈ TIM-barrel motif, similar to allergenic β-1,3-glucanases from banana (Mus a 5) and rubber tree latex (Hev b 2). Amino acid sequence alignment of these proteins indicated that the two-consensus IgE epitopes identified on the molecular surfaces of Mus a 5 and Hev b 2 were highly conserved in CJP38. Their conformations and surface locations were quite similar for these proteins. Sequence and structural conservation of these regions suggest that CJP38 is a candidate allergen responsible for the pollen-latex-fruit syndrome relating to Japanese cedar pollinosis.