Examples for left-handed alpha-helices?

Mitchell Isaacs misaacs at spam_me_not.student.usyd.edu.au
Mon Jun 11 20:45:52 EST 2001

"Ellie Brown" <ebrown at i-2000.com> wrote in message
news:ebrown-1106012040160001 at dyn26.access4.nyc.i-2000.net...
> However, the collagen triple helix is not an alpha helix.
The article doesn't claim that - in fact it says, "This triple helix has a
Right Handed Twist".

The left handed helix is 2° structure, whether or not it is an alpha-helix I
don't know. I also can't vouch for the accuracy of this article, and I have
to admit that I know very little about collagen. One thing that is worth
noting, however, is that this left-handed helix is glycine rich (the only
non-L-amino acid).


> Ellie brown
> In article <Z1BU6.119623$ff.894474 at news-server.bigpond.net.au>, "Mitchell
> Isaacs" <misaacs at spam_me_not.student.usyd.edu.au> wrote:
> > "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
> > 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
> > but if you did it would be with glycines (no side chain, no steric
> > hindrance - glycine is not optically active). Glycine residues adopting
> > 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
> > Handed Helix containing 3.3 amino acids per turn.  Three
> > molecules, three left handed helixes combine to form a triple helix -
> > Collagen Triple Helix or Tropocollagen.  This triple helix has a Right
> > Handed Twist, and contains ten X-GLY-Y repeat units per turn.  The
> > residues of the collagen molecule line up on the interior of the triple
> > helix.  Tropocollagen triple helixes associate with each other to form
> > strong fibers.  The triple helixes associate with each other in a
> > overlapping fashion involving 75 to 80% of the molecule."
> >
> > Cheers,
> > Mitchell

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