another GST story #2
terryh at ento.csiro.au
Mon Jul 18 06:56:26 EST 1994
On 15 Jul 1994 15:14:16 GMT, Stephen R. Lasky wrote:
(some stuff deleted)
>>In general though, we use denaturation in the presence of SDS so that a
>>protein will migrate at a rate relative to its mass and not be effected by
>>amino acid composition.
>That's the generally accepted therory and, no doubt, many if not most
>proteins fit nicely into that scheme. But there are exceptions, just one
>example (might be interesting for Jean-Marc and Emma): There is a protein
>called dTAF40 because on a SDS gel it has the apparent molecular mass of 40
>kd. Molecular cloning of the cDNA revealed a molecular mass of only 29 kd
>(Cell 75, 519-530, 1993). Could anybody kindly give an explanation for this
>unusual migration on a SDS gel?
>Inst. Biol. Chem.
It is highly likely that the proteins in your question
that migrate as larger proteins on SDS-PAGE have a high proline
content. This phenomenon involving proline has been noted many
times before; for
example see Pham and Sivasubarmanian in GENE 122, 345 (1993) or
Ziemer, Mason and Carlson in JBC 257, 11176 (1982). My own
personal experience with such a protein is one from an insect
small RNA virus which is 17 kDa yet migrates at Mr = 24k (>140%
more apparent MW).
It is a PEST protein (a property correlated with rapid turnover
and possessed by many regulatory genes and oncogenes) and has a
49% of P, E, S, and T.
However, to the nub of your question as to why proline does this,
I and the literature I've seen are still unaware. Anybody else
have a handle on this?
Terry Hanzlik, terryh at ento.csiro.au
CSIRO Division of Entomology
Canberra, ACT 2601
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