Googling peg polydispersity returns this as the second hit
http://www.springerlink.com/content/tp643l7678048447/
which is circa 1973 data from behind the iron curtain. The technology
may have improved, and the most recent I can quickly find is this paper
Plata et al., Electrophoresis, (2010), 31:679
Seems like PEG1000 would have anywhere between 15-30 monomers.
Cheers,
Ed.
On Thu, 2010-08-12 at 20:30 +0000, MARTYN SYMMONS wrote:
> That's a good point, Ed
>
> Based on the formula: HO CH2-(CH2-O-CH2)n-CH2OH, PEG MW = 44n+62, a table of n to MW goes like below which gives an idea of what range is possible. Someone maybe knows what polydispersity can be expected from the synthetic process. As you say though, a specific range could partition out of the bulk to the protein surface. And the main point of the original post was that only a subset of atoms in the bound PEG may be ordered enough to see.
> n MW
> 5, 282.
> 6, 326.
> 7, 370.
> 8, 414.
> 9, 458.
> 10, 502.
> 11, 546.
> 12, 590.
> 13, 634.
> 14, 678.
> 15, 722.
> 16, 766.
> 17, 810.
> 18, 854.
> 19, 898.
> 20, 942.
> 21, 986.
> 22, 1030.
> 23, 1074.
> 24, 1118.
> 25, 1162.
> 26, 1206.
> 27, 1250.
> 28, 1294.
> 29, 1338.
> 30, 1382.
> 31, 1426.
> 32, 1470.
> 33, 1514.
> 34, 1558.
> 35, 1602.
> 36, 1646.
> 37, 1690.
> 38, 1734.
> 39, 1778.
> 40, 1822.
> 41, 1866.
> 42, 1910.
> 43, 1954.
> 44, 1998.
> 45, 2042.
> 46, 2086.
> 47, 2130.
>
>
>
> --- On Thu, 12/8/10, Ed Pozharski <[log in to unmask]> wrote:
>
> > From: Ed Pozharski <[log in to unmask]>
> > Subject: Re: [ccp4bb] PEG in the pdb?
> > To: [log in to unmask]
> > Date: Thursday, 12 August, 2010, 17:35
> > PEG solutions contain fragments of
> > all sizes - it is the average size
> > (however defined by the manufacturer) that is 1000.
> > So technically it
> > is incorrect to claim that you have PEG1000 molecules bound
> > to your
> > protein, it is most likely much shorter fragments that can
> > penetrate the
> > channels in protein crystals.
> >
> > It's not a lot of work to generate monomer libraries for
> > peg fragments
> > of different length (and some are available from standard
> > monomer
> > libs).
> >
> > I always wondered why PEG is not defined in the standard
> > libraries as a
> > polymer - perhaps because it is rarely needed. Or is
> > it?
> >
> > Ed.
> >
> > On Thu, 2010-08-12 at 08:16 +0000, Klaus Sengstack wrote:
> > > Hi everybody,
> > >
> > > I just solved the structures of an enzyme an some
> > variants. In the
> > > active site cavity of each variant I found one or two
> > fragments of
> > > PEG1000 bound. I used PEG1000 in the crystallization
> > condition. Among
> > > the enzyme variants the number of non-hydrogen atoms
> > of these PEG
> > > fragments varies between 7 and 19 atoms. Now I want to
> > deposit the
> > > structures in the pdb and my question is, if I have to
> > define each
> > > fragment as a single ligand (what would be a lot of
> > work) or can I
> > > define them as PEG1000 molecules? Thanks.
> > >
> > > K.S.
> > >
> > >
> >
> > --
> > "I'd jump in myself, if I weren't so good at whistling."
> >
> >
> > Julian, King of Lemurs
> >
>
--
Edwin Pozharski, PhD, Assistant Professor
University of Maryland, Baltimore
----------------------------------------------
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