Studies on the Enhancement of Silk Proteins of Silkworm (Bombyx Mori L.) Using Low-Dose Gamma Irradiation and their Thermostability Properties

Abstract

This study was aimed to perceive whether low dose gamma irradiation could enhance the silk proteins of the silkworm, Bombyx mori and to understand their thermal stability properties. At initial stage of this study different extraction procedures of silk proteins were also tried to choose the best extraction procedures. The extraction of silk proteins from the silk gland was conducted in water and in sodium phosphate buffer at pH 7.4. Extraction of silk proteins in water was found to be suitable than the extraction in alkaline sodium phosphate buffer solution. Silk proteins became gelatinized very quickly when extracted in alkaline buffer solution. On the other hand, silk proteins extracted in water remained liquid for at least a week in cold (4°C). This study confirmed that low dose gamma irradiation (1.5 Gy) to embryonic stage could enhance the production of silk proteins. Comparing the proteins from the unirradiated silkworm, significant increase (48.97%) of silk proteins was obtained from the silk gland of irradiated silkworm. Results of thermal stability study showed that both Heavy (~350 kDa) and Light (~30 kDa) chain of fibroin protein were more stable than the sericin protein. Both the chains of fibroin protein could withstand at least 90°C for 10 minutes when extracted in water. But at 90°C, the H-chain of fibroin was found degraded when silk proteins were extracted in alkaline buffer solution. Silk fibroin (both H and L chain) was found quite stable up to 30 minutes at 90°C when extracted from the irradiated silkworm. But L-chain of the fibroin was lost completely at 90°C in 30 minutes. This study suggests the probable presence of hot spot in the genome of silkworm B. mori which is prone to be mutated at low dose gamma irradiation. The increased production of 48.97% silk proteins and the increased thermostability of the L-chain of fibroin from the irradiated silkworm larvae are probably the results of such mutation. This study also cautiously suggests the presence of a dimmer of H-chain of silk fibroin.