Ectopic expression of sericin enables efficient production of ancient silk with structural changes in silkworm

Abstract

Bombyx mori silk is a super-long natural protein fiber with a unique structure and excellent performance. Innovative silk structures with high performance are in great demand, thus resulting in an industrial bottleneck. Herein, the outer layer sericin SER3 is ectopically expressed in the posterior silk gland (PSG) in silkworms via a piggyBac-mediated transgenic approach, then secreted into the inner fibroin layer, thus generating a fiber with sericin microsomes dispersed in fibroin fibrils. The water-soluble SER3 protein secreted by PSG causes P25’s detachment from the fibroin unit of the Fib-H/Fib-L/P25 polymer, and accumulation between the fibroin layer and the sericin layer. Consequently, the water solubility and stability of the fibroin-colloid in the silk glandular cavity, and the crystallinity increase, and the mechanical properties of cocoon fibers, moisture absorption and moisture liberation of the silk also improve. Meanwhile, the mutant overcomes the problems of low survival and abnormal silk gland development, thus enabling higher production efficiency of cocoon silk. In summary, we describe a silk gland transgenic target protein selection strategy to alter the silk fiber structure and to innovate its properties. This work provides an efficient and green method to produce silk fibers with new functions.

Sericin Ser3 Ectopic Expressed in Posterior Silk Gland Affects Hemolymph Immune Melanization Response via Reducing Melanin Synthesis in Silkworm

“…In our previous study, we found that there was no significant difference between the growth and development of SER silkworms and WT under normal conditions [ 1 ]. In order to explore whether there were differences under stress conditions, we investigated the growth and development of 4L2d and 5L4d silkworm larvae after 40 °C high temperature shock for 3 h ( Figure 5 e–h).…”

“…In our previous study, it was found that the survival ability of SER larvae infected with E. coli and S. aureus was higher than that of WT [ 1 ], which may be related to the significantly increased AMPs level of SER silkworms. In addition to the survival and development of insects being closely related to bacteria and other microorganisms, their physiology and metabolism are also very sensitive to temperature.…”

“…The mutant pure line SER is a recombinant Ser3 gene specifically expressed in the middle silk gland and posterior silk gland. It was created by this laboratory, and WT is its wild type [ 1 ]. The silkworm larvae were fed with fresh mulberry leaves under natural light at 25.0 °C ± 2.0 °C.…”

“…The superior performance of silk fibers produced by the silkworm is widely used in textile engineering. The silkworm’s silk gland (SG) bioreactor has remarkable protein synthesis ability, which is favored by biomaterial and biomedical researchers [ 1 , 2 ], and can be used to produce growth factors, tumor antigen proteins, human connective tissue growth factor (CTGF), recombinant human fibrinogen (rFib) and other biomedical proteins with good biological activity [ 3 , 4 , 5 , 6 ]. At the same time, silk gland transgenes based on textile engineering applications have also developed multifunctional silk fibers with improved silk fiber or special properties [ 7 , 8 ].…”

“…This study used the pure line SER material of the silkworm mutant with the self-silk protein gene, which is specific for the silk gland tissue. The growth and development of silk glands and individuals did not have adverse problems, with the silk protein production capacity of the silk gland exceeding that of the wild type (WT), and the recombinant Ser3 fragment of the mutant was not inserted into the functional gene site [ 1 ]. Through the influence mechanism of SER silkworm hemolymph melanization ability, this study discussed the influence of silk gland transgenicity on the melanization process of silkworms and the redox metabolism of hemolymph in vivo, to provide a reference at the molecular level for promoting the safe evaluation and development of transgenic silkworms.…”