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Spidroin, N-terminal | |||||||||
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Identifiers | |||||||||
Symbol | Spidroin_N | ||||||||
Pfam | PF16763 | ||||||||
InterPro | IPR031913 | ||||||||
CATH | 2lpj | ||||||||
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Spidroin, C-terminal | |||||||||
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Identifiers | |||||||||
Symbol | Spidroin_MaSp | ||||||||
Pfam | PF11260 | ||||||||
InterPro | IPR021001 | ||||||||
CATH | 2m0m | ||||||||
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Spidroin-1 | |||||||
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Identifiers | |||||||
Organism | |||||||
Symbol | ? | ||||||
UniProt | P19837 | ||||||
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Spidroin-2 | |||||||
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Identifiers | |||||||
Organism | |||||||
Symbol | ? | ||||||
UniProt | P46804 | ||||||
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Spidroins are the main proteins in spider silk. Different types of spider silk contain different spidroins, all of which are members of a single protein family. [1] The most-researched type of spidroins are the major ampullate silk proteins (MaSp) used in the construction of dragline silk, the strongest type of spider silk. Dragline silk fiber is made up of two types of spidroins, spidroin-1 (MaSp1) and spidroin-2 (MaSp2). [2] [3]
Spidroin is part of a large group of proteins called scleroproteins. This group includes other insoluble structural proteins such as collagen and keratin.
A fiber of dragline spidroin is as thick and resistant as one of steel but is more flexible. It can be stretched to approximately 135% of its original length without breaking. Its properties make it an excellent candidate for use in various scientific fields. [4]
Major ampullate spidroins are large proteins with an extension of 250-350 kDa, with an average of 3500 amino acids. They represent a polymeric organization, mostly based on highly homogenized tandem repeats. There are 100 tandem copies of 30 to 40 amino acids which repeat sequence and they represent more than 90% of the protein sequence. [5] Alanine and glycine residues are the most abundant amino acids in these proteins. Alanine appears in blocks of six to fourteen units that form β-sheets. These alanine blocks can stack to create crystalline structures in the fiber, linking different protein molecules together. Glycine is present in different motifs, such as GGX and GPGXX (where X = A, L, Q, or Y), that also have specific secondary structures (3 10 helix and β-spiral, respectively). Glycine-rich regions are more amorphous and contribute to extensibility and flexibility. Some of the differences observed between spidroin 1 and spidroin 2 (the most important major ampullate spidroins) are the proline content, which is very low in the first one but significant in the second one, and the motifs. Motif (GGX)n is characteristic in spidroin 1, while GPG and QQ are typical in spidroin 2.
On the other hand, spidroins have non-repetitive amino (N) and carboxyl (C) terminal domains of approximately 150 and 100 amino acids respectively. N- and C-terminal domains share little resemblance, except that they are both rich in serine and both are largely amphipathic α-helical secondary structures. These domains are conserved not only between spidroin 1 and 2, but also among many silk types and spider species. Experimental data show the N- and C-terminal domains contribute to fiber assembly. [6] The C-terminal domain is involved in the organized transition from a soluble spidroin solution to an insoluble fiber during spinning. [7] In the N-terminal domain, there are signal peptides which regulate spidroin secretion from silk gland cells. [8] [9]
An individual spider spins a multitude of silk types, with each type emerging from its own distinctive set of abdominal silk glands. This complex silk machinery enables spiders to use task-specific silks (e.g., for web assembly, egg-case construction, prey wrapping, etc.). [9] The different types of silk (major ampullate silk, minor ampullate silk, flagelliform silk, aciniform silk, tubiliform silk, pyriform silk, and aggregate silk) [10] are composed of different types of proteins.
Dragline silk is mainly formed by spidroin proteins. It is a type of major ampullate silk and is produced in the major ampullate gland. Dragline silk is used not only to construct the outer frame and radii of the orb-shaped web but also as a hanging lifeline that allows the spider to evade and/or escape from predators. [11] The major ampullate gland that produces this silk is formed by three main sections: a central bag (B zone) flanked by a tail (A zone) and a duct heading towards the exit. The tail secretes most of the “spinning dope”, a solution which contains the protein molecules that will constitute the silk fiber. The sac is the main storage repository.
The epithelium of the A zone is composed of tall columns of secretory cells of a single type, packed with secretory granules. The major component of these cells which secrete the fibroin solution is a 275kDa protein containing the polypeptides spidroin I and spidroin II. The output of these cells is an aqueous and highly viscous solution of about 50% protein (mostly spidroin). The product secreted makes up the dragline silk, the main structure.
This highly viscous protein emulsion flows into the B zone, where it is covered by glycoproteins. After exiting this bag, the liquid is funneled into the narrow duct. As the gelatinous protein solution moves into the duct, the integral spidroins and glycoproteins are gradually distorted into long, thin, aligned figures with the direction of the flow. Then, they are stretched and lined up in a way that will eventually allow them to create strong intermolecular links. After different processes the silk is extended in the spinning channel to form an extremely tough thread.
In the last decade, much research has been done about spidroin protein and spider silk in order to take advantage of some of its properties, such as its elasticity and strength. Spider silk is used in different industries, and its range of applications in biomedicine is increasing every day. For example, the military and defense industries use bulletproof vests made from these fibers.
Recombinant spidroin has been successfully obtained in both eukaryotic and prokaryotic cells although there were some difficulties in the procedure due to the length of the gene sequence. Thanks to expression and the cloning work, it is possible to obtain large-scale production of spidroin which provides new opportunities for the manufacture of new biomaterials. [12] There have been attempts to generate transgenic tobacco and potato plants that express remarkable amounts of recombinant Nephila clavipes dragline proteins. [13]
Furthermore, fibers developed from spidroin are tolerated in vitro, in cell culture, and in vivo, in animals like pigs, as no signs of either inflammatory response nor body reaction were shown to these fibers. These results suggest that they could be used in medicine without risk of biocompatibility issues and thus potentially lead to many new opportunities in tissue engineering and regenerative medicine.
The way spiders produce spidroin in micelles has inspired a method of mass-producing recombinant proteins. By fusing a pH-insensitive, charge-reversed mutant of spidroin N-terminal domain to the proteins to produce, much more soluble proteins can be produced in E. coli. [14]
Tubuliform (egg case) silk strands structural domain | |||||||||
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Identifiers | |||||||||
Symbol | RP1-2 | ||||||||
Pfam | PF12042 | ||||||||
InterPro | IPR021915 | ||||||||
CATH | 2mqa | ||||||||
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Silk proteins present in other spider silk types are also occasionally referred to as spidroin. These include tubuliform silk protein (TuSP), flagelliform silk protein (Flag; O44358 - Q9NHW4 - O44359 ), minor ampullate silk proteins (MiSp; K4MTL7 ), aciniform silk protein (AcSP), pyriform silk protein (PySp) and aggregate silk glue (ASG2/AgSp). These different silk proteins along with MaSP show some level of homology to each other, in protein domains, repeats, and in promoters, but also have their own unique features and variations on these parts to furfill their different functions. [15] [16] [17] These commonalities point at a common origin of proteins found in all these different types of silks. [1] [9]
In July 2020 a team of RIKΞN researchers report that they succeeded in using a genetically altered variant of R. sulfidophilum to produce spidroins. [18] [19]
Keratin is one of a family of structural fibrous proteins also known as scleroproteins. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, horns, claws, hooves, and the outer layer of skin among vertebrates. Keratin also protects epithelial cells from damage or stress. Keratin is extremely insoluble in water and organic solvents. Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in reptiles, birds, amphibians, and mammals. Excessive keratinization participate in fortification of certain tissues such as in horns of cattle and rhinos, and armadillos' osteoderm. The only other biological matter known to approximate the toughness of keratinized tissue is chitin. Keratin comes in two types, the primitive, softer forms found in all vertebrates and harder, derived forms found only among sauropsids.
Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity (sericulture). The shimmering appearance of silk is due to the triangular prism-like structure of the silk fibre, which allows silk cloth to refract incoming light at different angles, thus producing different colors.
Spider silk is a protein fibre or silk spun by spiders. Spiders use silk to make webs or other structures that function as adhesive traps to catch prey, to entangle and restrain prey before biting, to transmit tactile information, or as nests or cocoons to protect their offspring. They can also use the silk to suspend themselves from height, to float through the air, or to glide away from predators. Most spiders vary the thickness and adhesiveness of their silk for different uses.
Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. Secreted extracellular proteins are often glycosylated.
Intermediate filaments (IFs) are cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate Branchiostoma.
A signal peptide is a short peptide present at the N-terminus of most newly synthesized proteins that are destined toward the secretory pathway. These proteins include those that reside either inside certain organelles, secreted from the cell, or inserted into most cellular membranes. Although most type I membrane-bound proteins have signal peptides, the majority of type II and multi-spanning membrane-bound proteins are targeted to the secretory pathway by their first transmembrane domain, which biochemically resembles a signal sequence except that it is not cleaved. They are a kind of target peptide.
Elastin is a protein that in humans is encoded by the ELN gene. Elastin is a key component of the extracellular matrix in gnathostomes. It is highly elastic and present in connective tissue allowing many tissues in the body to resume their shape after stretching or contracting. Elastin helps skin to return to its original position when it is poked or pinched. Elastin is also an important load-bearing tissue in the bodies of vertebrates and used in places where mechanical energy is required to be stored.
Laminins are a family of glycoproteins of the extracellular matrix of all animals. They are major constituents of the basement membrane, namely the basal lamina. Laminins are vital to biological activity, influencing cell differentiation, migration, and adhesion.
Trichonephila clavipes, commonly known as the golden silk orb-weaver, golden silk spider, or colloquially banana spider, is an orb-weaving spider species which inhabits forests and wooded areas ranging from the southern US to Argentina. It is indigenous to both continental North and South America. Known for the golden color of their silk, the large size of their females, and their distinctive red-brown and yellow coloring, T. clavipes construct large, asymmetrical circular webs attached to trees and low shrubs in woods to catch small- and medium-size flying prey, mostly insects. They are excellent web-builders, producing and utilizing seven different types of silk, and they subdue their prey by injecting them with venom, as opposed to related species which immobilize their prey by wrapping them in silk first. They are not known to be aggressive towards humans, only biting out of self-defense if touched, and their relatively harmless venom has a low toxicity, posing little health concern to healthy human adults. Due to their prevalence in forests, T. clavipes may be encountered by hikers.
BioSteel was a trademark name for a high-strength fiber-based material made of the recombinant spider silk-like protein extracted from the milk of transgenic goats, made by defunct Montreal-based company Nexia Biotechnologies, and later by the Randy Lewis lab of the University of Wyoming and Utah State University. It is reportedly 7-10 times as strong as steel if compared for the same weight, and can stretch up to 20 times its unaltered size without losing its strength properties. It also has very high resistance to extreme temperatures, not losing any of its properties within −20 to 330 degrees Celsius.
Pilin refers to a class of fibrous proteins that are found in pilus structures in bacteria. These structures can be used for the exchange of genetic material, or as a cell adhesion mechanism. Although not all bacteria have pili or fimbriae, bacterial pathogens often use their fimbriae to attach to host cells. In Gram-negative bacteria, where pili are more common, individual pilin molecules are linked by noncovalent protein-protein interactions, while Gram-positive bacteria often have polymerized LPXTG pilin.
Thrombospondin 1, abbreviated as THBS1, is a protein that in humans is encoded by the THBS1 gene.
Fibroin is an insoluble protein present in silk produced by numerous insects, such as the larvae of Bombyx mori, and other moth genera such as Antheraea, Cricula, Samia and Gonometa. Silk in its raw state consists of two main proteins, sericin and fibroin, with a glue-like layer of sericin coating two singular filaments of fibroin called brins. Silk fibroin is considered a β-keratin related to proteins that form hair, skin, nails and connective tissues.
Surfactant protein C (SP-C), is one of the pulmonary surfactant proteins. In humans this is encoded by the SFTPC gene.
Nerve tissue is a biological molecule related to the function and maintenance of normal nervous tissue. An example would include, for example, the generation of myelin which insulates and protects nerves. These are typically calcium-binding proteins.
Surfactant protein A1(SP-A1), also known as Pulmonary surfactant-associated protein A1(PSP-A) is a protein that in humans is encoded by the SFTPA1 gene.
Discoidin domain is major protein domain of many blood coagulation factors.
A dermal patch or skin patch is a medicated adhesive patch placed on human skin to deliver a medication into the skin. This is in contrast to a transdermal patch, which delivers the medication through the skin and into the bloodstream.
Sericin is a protein created by Bombyx mori (silkworms) in the production of silk. Silk is a fibre produced by the silkworm in production of its cocoon. It consists mainly of two proteins, fibroin and sericin. Silk consists of 70–80% fibroin and 20–30% sericin; fibroin being the structural center of the silk, and sericin being the gum coating the fibres and allowing them to stick to each other.
The BRICHOS family consists of a variety of proteins linked to major diseases, each containing a 100 amino acid BRICHOS domain that is thought to have a chaperone function. These include BRI2, which is related to familial British and Danish dementia ; Chondromodulin-I, related to chondrosarcoma; CA11, related to stomach cancer; and surfactant protein C (SP-C), related to respiratory distress syndrome (RDS).