"Eckart Bindewald" <bindewald at ti.uni-mannheim.de> wrote in message
news:3B224173.7C6F9DFA at ti.uni-mannheim.de...
> Hello!
>> Often it is cited, that left-handed alpha-helices are very rare in
proteins, but DO exist. However,
> I could not find a reference to an example structure. Who can inform me
about a protein structure
> which contains a left-handed alpha-helix (PDB codes preferred)?
I don't think you can get an extensive left-handed helix with L-amino acids,
but if you did it would be with glycines (no side chain, no steric
hindrance - glycine is not optically active). Glycine residues adopting the
left-handed helical position are quite common - check out
http://www.expasy.org/swissmod/course/text/chapter2.htm
Actually, one that may interest you: I took this from
http://academic.mu.edu/bisc/siebenlistk/413proteinstructure.pdf
"Protropocollagen is the monomer unit and this molecule folds into a Left
Handed Helix containing 3.3 amino acids per turn. Three protropocollagen
molecules, three left handed helixes combine to form a triple helix - The
Collagen Triple Helix or Tropocollagen. This triple helix has a Right
Handed Twist, and contains ten X-GLY-Y repeat units per turn. The glycine
residues of the collagen molecule line up on the interior of the triple
helix. Tropocollagen triple helixes associate with each other to form long
strong fibers. The triple helixes associate with each other in a staggered
overlapping fashion involving 75 to 80% of the molecule."
Cheers,
Mitchell
