Customized Flagelliform Spidroins Form Spider Silk-like Fibers at pH 8.0 with Outstanding Tensile Strength

Xue Li,Gefei Chen,Jan Johansson,Yu-Ming Cai,Rui Wen,Rui Zhang,Xingmei Qi,Yuan Sun,Qing Meng

doi:10.1021/acsbiomaterials.1c01354

Abstract

Spider flagelliform silk shows the best extensibility among various types of silk, but its biomimetic preparation has not been much studied. Herein, five customized flagelliform spidroins (FlSps: S and NTDFl-Sn-CTDFl, n = 1–4), in which the repetitive region (S) and N-/C- terminal domains (NTDFl and CTDFl) are from the same spidroin and spider species, were produced recombinantly. The recombinant spidroins with terminal domains were able to form silk-like fibers with diameters of ∼5 μm by manual pulling at pH 8.0, where the secondary structure transformation occurred. The silk-like fibers from NTDFl-S4-CTDFl showed the highest tensile strength (∼250 MPa), while those ones with 1–3 S broke at a similar stress (∼180 MPa), suggesting that increasing the amounts of the repetitive region can improve the tensile strength, but a certain threshold might need to be reached. This study shows successful preparation of flagelliform silk-like fibers with good mechanical properties, providing general insights into efficient biomimetic preparations of spider silks.

Highlights

Orb-weaving spiders produce up to seven types of silks with various mechanical properties for different biological purposes (Figure 1A).[1−3] Spider silk as a biomaterial possesses outstanding mechanical properties,[1,4] and excellent biocompatibility and biodegradability, holding great potential in biomedicine.[5,6] Due to spiders’ innate territorial behavior and limited amounts of silks from a spider web, it is not realistic to obtain spider silk on a large scale via farming spiders
Dragline silk is made up of major ampullate spidroins (MaSps) with poly (A)n motifs contributing to strength by forming β-sheet crystal structures,[2] while flagelliform silk is composed of flagelliform spidroins (FlSps) that are rich in GPGGX (X is mainly for S or Y) motifs, resulting in intriguing extensibility, possibly through spring structures.[3,7]
These functional motifs confer flagelliform silk the best extensibility among other spider silks as well as excellent strength, and it has been shown that the GPGGX, GGX, and spacer motifs contribute to extensibility, toughness, and strength, respectively, in synthetic silk-like fibers.[8−10] While several studies have looked into the preparation of artificial flagelliform silk, only a few chimeric FlSp/MaSp spidroins were successfully constructed for producing spider silk-like fibers,[11−14] which might be due to the fact that FlSp contains highly repetitive units rich in Gly and Pro, making it difficult to be expressed in exogenous systems

Summary

Introduction

Orb-weaving spiders produce up to seven types of silks with various mechanical properties for different biological purposes (Figure 1A).[1−3] Spider silk as a biomaterial possesses outstanding mechanical properties,[1,4] and excellent biocompatibility and biodegradability, holding great potential in biomedicine.[5,6] Due to spiders’ innate territorial behavior and limited amounts of silks from a spider web, it is not realistic to obtain spider silk on a large scale via farming spiders. The core repetitive region is made up of 11 repetitive units that are built by iterations of the GPGGX, GGX (X is mainly for S, Y, or A), and hydrophobic spacer motifs.[7] These functional motifs confer flagelliform silk the best extensibility among other spider silks as well as excellent strength, and it has been shown that the GPGGX, GGX, and spacer motifs contribute to extensibility, toughness, and strength, respectively, in synthetic silk-like fibers.[8−10] While several studies have looked into the preparation of artificial flagelliform silk, only a few chimeric FlSp/MaSp spidroins were successfully constructed for producing spider silk-like fibers,[11−14] which might be due to the fact that FlSp contains highly repetitive units rich in Gly and Pro, making it difficult to be expressed in exogenous systems. NTD and CTD are highly conserved with regard to the tertiary structure, where NTD adopts a five α-helix structure that dimerizes into an antiparallel dimer at low pH15−23 and CTD is a parallel dimer

Methods

Results

Discussion

Conclusion