Repetitive domains

Elmoijani, K., Thievin, M., Michon, T., Popineau, Y., HaUet, J.N., and Gueguen, J., Synthetic genes specifying periodic polymers modelled on the repetitive domain of wheat gliadins Conception and expression, Biochem. Biophys. Res. Commun., 239(1), 240-246, 1997. 

Under the electron microscope titin appears as a flexible beaded string 4 nm in diameter. Most of the molecule is made up of repetitive domains of two types. In human cardiac titin there are 132 folded domains that resemble type III fibronectin repeats and 112 immunoglobulin-like domains.98 In a "PEVK region," between residues 163 and 2174, 70% of the residues are Pro, Glu, Val, or Lys. The titin molecule may be organized as polyproline helices in this elastic region.1023 At the C terminus of titin 800 residues, including a Ser / Thr protein kinase domain, are found within the M-line. 

A large number of gene sequences are now available for HMW subunits, showing that they typically comprise between 630 and 820 amino acids, with M, ranging from 67,500 to 88,000 (Shewry et al. 2003). Their sequences can be divided into three domains, an extensive central domain consists of repeated sequences based on two or three peptide motifs, hexapeptides (consensus Pro.Gly.Gln.Gly.Gln.Gln), nonapeptides (consensus Gly.Tyr.Tyr.Pro.Thr.Ser.Pro/Leu.Gln.Gln) and tripeptides (consensus Gly.Gln.Gln) which vary in length from 420 to 700 residues. These repetitive domains are flanked by shorter non-repetitive domains which vary in length between 81 to 104 residues at the A-terminus and 42 residues at the C-terminus. The non-repetitive N- and C-terminal domains contain most or all of the cysteine residues available for inter-chain covalent bonding. 

The HMW subunits therefore display the characteristics required of an elastomeric material. These are an extensive central repetitive domain that is unconstrained by covalent cross-links and can undergo structural changes on deformation and shorter N- and C-terminal domains in which cross-linking can occur. 

Figure 6.1. The role of HMW subunits in gluten structure and functionality. Amino acid sequences derived from direct analysis of purified proteins and the isolation and sequencing of corresponding genes show that the proteins have highly conserved structures, with repetitive domains flanked by shorter nonrepetitive domains containing cysteine residues (SH) available for formation of interchain disulphide bonds. Molecular modelling indicates that the individual repetitive domains form a loose spiral structure (bottom right) while SPM shows that they interact by noncovalent forces to form fibrils (centre right). Includes figures from Parchment et al. (2001) and Humphries et al. (2000).

Parchment, O., Tatham A.S., Shewry, P.R., and Osguthorpe, D.J. (2001). Molecular modelUng of the central repetitive domains of the high molecular weight subunits of wheat. Cereal Chem., 49, 268-275. 

Repetitive domain (crops] Hydrophobic region potential nucleotide bindinB site... 

Figure 13.12 Structural aspects of the x- and y-type HMW-GS gene. The two HMW-GS types have a similar structure a central repetitive domain comprising repeats of six, nine and 15 amino acids and smaller terminal domains containing most of the cysteine residues (disulfide bonds are indicated by S The x-type HMW-GSs apparently have one intramolecular disulfide bond within the N-terminus, and the y-type is likely to have two such bonds, thus reducing the cysteines available for forming intermolecular bonds necessary for producing the glutenin macro-polymer [53].

A second property of the HMW subunits which could relate to elasticity are the properties of the 3-turn rich spiral supersecondary structure formed by their repetitive domains. It has been suggested that this structure is intrinsically elastic and contributes directly to the elasticity of the glutenin polymers [66]. 

Silks are encoded by highly repetitive structural genes that are under tight regulatory control in the cell. The repetitive domains influence the higher-order conformation and result in fibers with unusual functional properties. Information on the sequences of several kinds of spider silks have been rapidly aecumulated recently, the complete. sequence has been reported for silk fibroin from B. mori silk fibroin heavy chain. ... 

In the repetitive domain there are two types of repeat units (Fig. 2). One unit is characterized by GlyAlaGlyAlaGlySer the other unit is the peptides of Gly Ala repeats followed by GlyTyr. 

GAGAGYGAGAG (2) ondGAGVGYGAGAG (3) selected from the repetitive domains ofB. mori silk fibroin. indicates spinning side bande. 

Lyons, R.E., Naim, K.M., Huson, M.G. et al. (2009) Comparisons of recombinant resilin-like proteins repetitive domains are sufficient to confer resUin-like properties. Biomacrotnolecules, 10, 3009-3014. 

Ittah, S., Barak, N., Gat, U., 2010. Apioposed model for dragline spider silk self-assembly insights from the effect of the repetitive domain size on fiber properties. Biopolymers 93 (5), 458—468. 

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