The role of terminal domains during storage and assembly of spider silk proteins

Abstract

Fibrous proteins in nature fulfill a wide variety of functions in different structures ranging from cellular scaffolds to very resilient structures like tendons and even extra‐corporal fibers such as silks in spider webs or silkworm cocoons. Despite their different origins and sequence varieties many of these fibrous proteins share a common building principle: they consist of a large repetitive core domain flanked by relatively small non‐repetitive terminal domains. Amongst protein fibers, spider dragline silk shows prominent mechanical properties that exceed those of man‐made fibers like Kevlar. Spider silk fibers assemble in a spinning process allowing the transformation from an aqueous solution into a solid fiber within milliseconds. Here, we highlight the role of the non‐repetitive terminal domains of spider dragline silk proteins during storage in the gland and initiation of the fiber assembly process. © 2011 Wiley Periodicals, Inc. Biopolymers 97: 355–361, 2012.

Ion and seed dependent fibril assembly of a spidroin core domain

“…Natural spider silk assembly requires the presence of regulatory N-and C-terminal domains which allow the parallel orientation of b-sheets as well as very fast assembly in the range of milliseconds (Eisoldt et al, 2011(Eisoldt et al, , 2012Heidebrecht et al, 2015). In case of cross-b like fibrils, assembly is rather triggered by pre-formation of polyalanine structures within the respective spidroin, a process which is less controllable and much slower than assembly of natural full length spidroins.…”

The N-terminal domains of spider silk proteins assemble ultrafast and protected from charge screening

“…The NTD of spidroins evolved to maintain solubility of silk fibrebuilding blocks in the ampulla of the spinning gland and to assist their transformation into threads on demand 5 . The sequence composition of the NTD is unusual and its fold is unique with no homologue identified so far 7 .…”

“…The bulk of a spidroin sequence consists of repetitive peptide motifs of simple amino-acid composition. This central segment is flanked by non-repetitive, globular carboxy-and amino-terminal domains 3,5 . Spidroins have a molecular weight of about 300 kDa 1 and the non-repetitive terminal domains cover only B10% of the sequence area but have critical roles during silk synthesis 5 .…”

“…This central segment is flanked by non-repetitive, globular carboxy-and amino-terminal domains 3,5 . Spidroins have a molecular weight of about 300 kDa 1 and the non-repetitive terminal domains cover only B10% of the sequence area but have critical roles during silk synthesis 5 . At the beginning of the spinning process, a highly concentrated solution of spidroins is stored in the ampulla of the spinning gland.…”

From silk spinning in insects and spiders to advanced silk fibroin drug delivery systems

“…The role of the N-terminal domain is particularly well documented for the pH-dependent control of fiber formation, preventing premature formation of b-sheets at neutral pH and guiding fiber formation during acidification [61][62][63] and has been reviewed before [64,65]. The role of the C-terminus includes influence on both, storage and ordered assembly [66,67].…”