[Ari Ben Canaan]

Spider silk is composed mainly of alanine and glycine.

Is it correct to say that the amorphous regions and hence the elasticity of spider silk can be put down to glycine whilst the rigidity and the crystalline regions can be put down to alanine in Beta pleated sheets ?

[fledarmus]

Reasonably correct - polyalanine chains pack better into sheets, while polyglycine chains tend to form helices.

[sunshyn]

Hi, I just joined the forum and I would beg to differ! I believe the elasticity of spider silk is more due to its high proline content. Glycine is a part of the crystalline region as well, together with alanine they have small side chains which allow for regular packing, hence the crystalline structure. Proline on the other hand, Proline because of its structure  inhibits formation of alpha helices and promotes formation of the β-turn spiral structure that is believed to govern the elasticity and retraction force of spider silk. Hope this helps 

[AWK]

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2658765/
http://www.chm.bris.ac.uk/motm/spider/page3.htm
http://pubs.acs.org/doi/pdfplus/10.1021/bm700877g