Profiling of Silk Sericin from Cocoons of Three Southern African Wild Silk Moths with a Focus on Their Antimicrobial and Antioxidant Properties

Abstract

Silk sericin was extracted from the cocoons of three Southern African wild silk moth species, namely Gonometapostica, G. rufobrunnae (Lepidoptera: Lasiocampidae), and Argema mimosae (Lepidoptera: Saturniidae); these three sericin extracts were analysed to determine the relationship that exists between their chemical structures and their functional properties. The relationship was investigated by utilising several methods that include the determination of the amino acid composition, and characterisation of the secondary structures with Fourier transformation infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The antibacterial properties of these three sericin extracts were evaluated by an agar well diffusion assay with three Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus, and Staphylococcus epidermidis) as test microorganisms; and, lastly, the antioxidant properties of the three sericin extracts were determined using several scavenging methods that include the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS˙+), and the ferric reducing antioxidant power (FRAP) assay. The amino acid composition in the silk sericin extracts from G. postica, G. rufobrunnea, and Argema mimosa in terms of the polar/non-polar ratio (P/NP) was found to be 65:35, 56:44, and 59:41, respectively. The FTIR spectra of these three silk sericin extracts showed distinct major bands such as amide A (3265 cm−1), amide B (3062 cm−1), amide I (1644 cm−1), amide II (1538 cm−1), and amide III (1244 cm−1). The XRD patterns of the silk sericin extracts revealed both amorphous and α-helical structures, with small crystalline regions. All three silk sericin extracts presented potent antibacterial efficacy against the three Gram-positive bacteria and were found to have excellent antioxidant activities against the tested free radicals.

Exploring Silk Sericin for Diabetic Wounds: An In Situ-Forming Hydrogel to Protect against Oxidative Stress and Improve Tissue Healing and Regeneration

“…The results that were obtained in antimicrobial assessment of sericin solution are contradictory to some reported studies that demonstrated SS solution showing antimicrobial activity for S. aureus and E. coli [ 44 , 45 , 46 ]. Xue et al [ 47 ] investigated the interaction mechanism of E. coli cells that were treated with SS and SSH for wound healing.…”

The Evaluation of the Biological Effects of Melanin by Using Silkworm as a Model Animal

“…This is due to the fact that the amide I area of the spectrum is the most informative for determining protein secondary structure [45]. The FTIR spectra of amide I are presented in detail as deconvoluted FTIR spectra (Supplementary Figure S2), and the contents of the secondary structures are shown in Figure 4b, revealing that the melaninmodified silks contained more helix and random coil structures and a fewer β-sheets than the control silk, similar to previously reported results [46]. This may be attributed to the formation of hydrogen bonds between melanin and silk fibroins.…”

Response surface optimization of enzymatic hydrolysis and ROS scavenging activity of silk sericin hydrolysates

“… 2017 ; Manesa et al. 2020 ). It has been revealed that peptide characteristics, including molecular weight, amino acid sequence and hydrophobicity strongly determine its antioxidant potential (Karamać et al.…”