[RASMB] another vbar question

[Rufer, Arne]

Hi Holger,

would preferential hydration play a role at the very high NaCl
concentrations you are using? Regarding anecdotes on vbar, I can add that
when we worked with acylated peptides the vbar measured by densitometry
turned out to be much smaller than vbar calculated from the aa sequence +
modification. We had congruent AUC and SEC-MALLS data showing that certain
acylations led to oligomerisation, presumably due to an hydrophobic
interaction that became stronger with higher salt concentration. At that
time we argued the effect on vbar could be due to a solvent envelope for
packed acyl-moieties that is smaller than that of the separated
acyl-moieties. Makes sense? I am curious to read Mattia's comment on this,
too.

Best,

Arne





On Thu, Sep 28, 2017 at 3:48 PM, HGSR (Holger Martin Strauss) <
hgsr at novonordisk.com> wrote:

> Hello yall,
>
> Wow, vbar trending?!
>
> I actually have a question regarding the salt-dependency of the vbar. We
> are working with peptides modified with some organic linkers and a diacid
> (between C4-C50, to give a range). We measure the droh/dc (DMA5000) at
> different concentrations and calculate the vbar. Controls OK, concentration
> accurate and measurements reproducible, buffer dialysed. Salt-concentration
> is varied (NaCl, 5-1500 mM-ish). Turns out the vbar is considerably
> different at high salt. (And so is the self-association, btw.) No
> detergents or denaturants, just some additional phosphate for buffering,
> besides the NaCl.
>
>
>    - How can this be rationalised structurally?
>    - Any tests when droh/dc is more appropriate for Mw /sigma than vbar?
>    - Other examples in the literature for peptides?
>    - Any general comments/anectodes/remarks?
>
>
> Cheers,
>
> Holger
>
>
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>
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