[RASMB] glycosylation in sigma value

[Satinder Singh]

Hello,

I am dealing with a glycosylated protein (N-linked). The monomer molecular
weights determined from amino acid sequence and MALDI-TOF are 45,890 and 48,170,
respectively, so I am guessing that 2280 Da (or 5% of the protein's MW) is
due to glycosylation.

I calculated the partial specific volume with Sednterp (using the
sequence and a temp of 4C; Vbar = 0.7266) and then adjusted the value
using an estimated carbohydrate Vbar of 0.63 ml/g
The resulting value was 0.7220 ml/g.

I am wondering if this is the proper way to calculate Vbar of a
glycosylated protein if the precise carbohydrate content is unknown.

Another question: with an unglycosylated protein, I am had been using
Sednterp to calculate sigma from the amino acid composition. Since I do
not know the carbohydrate composition of the present protein, I obviously
cannot use a calculated sigma value. I had thought about directly
calculating it from the mass spec molecular weight using the equation
sigma = {MW*(1-[Vbar*solventdensity])w2}/RT, but again I am not sure if
this correct.

Could someone shed some light onto this?  (I will be using WinNONLIN for
fitting).

Thanks.

Satinder