Alternatingly twisted ß-hairpins and nonglycine residues in the disallowed II' region of the Ramachandran plot.

The structure of the SH3 domain of α-spectrin (PDB code 1SHG) features Asn47 in the II' area of the Ramachandran plot, which as a rule admits only glycine residues, and this phenomenon still awaits its explanation. Here, we undertook a computational study of this particular case by means of molecular dynamics and bioinformatics approaches. We found that the region of the SH3 domain in the vicinity of Asn47 remains relatively stable during denaturing molecular dynamics simulations of the entire domain and of its parts. This increased stability may be connected with the dynamic hydrogen bonding that is susceptible to targeted in silico mutations of Arg49. Bioinformatics analysis indicated that Asn47 is in the ß-turn of a distinctive structural fragment we called 'alternatingly twisted ß-hairpin.' Fragments of similar conformation are quite abundant in a nonredundant set of PDB chains and are distinguished from ordinary ß-hairpins by some surplus of glycine in their ß-turns, lack of certain interpeptide hydrogen bonds, and an increased chirality index. Thus, the disallowed conformation of residues other than glycine is realized in the ß-turns of alternatingly twisted ß-hairpins.

A novel model system for design of biomaterials based on recombinant analogs of spider silk proteins.

Spider dragline silk possesses impressive mechanical and biochemical properties. It is synthesized by a couple of major ampullate glands in spiders and comprises of two major structural proteins--spidroins 1 and 2. The relationship between structure and mechanical properties of spider silk is not well understood. Here, we modeled the complete process of the spider silk assembly using two new recombinant analogs of spidroins 1 and 2. The artificial genes sequence of the hydrophobic core regions of spidroin 1 and 2 have been designed using computer analysis of existing databases and mathematical modeling. Both proteins were expressed in Pichia pastoris and purified using a cation exchange chromatography. Despite the absence of hydrophilic N- and C-termini, both purified proteins spontaneously formed the nanofibrils and round micelles of about 1 microm in aqueous solutions. The electron microscopy study has revealed the helical structure of a nanofibril with a repeating motif of 40 nm. Using the electrospinning, the thin films with an antiparallel beta-sheet structure were produced. In summary, we were able to obtain artificial structures with characteristics that are perspective for further biomedical applications, such as producing three-dimensional matrices for tissue engineering and drug delivery.