Protein Degradation Problem
Eric E. Snyder
eesnyder at beagle
Wed Mar 23 16:57:46 EST 1994
I am posting this for a friend w/o usenet access. Please
send follow-ups to this address:
LUCK at NIEHS.NIH.GOV
We have a problem with a protein that may be helped by someone on the net.
Any remarks would be appreciated.
There is a very weird degradation of this protein.
The protein is stored in citrate at pH 5-6 Several breakdown products have
1) Modified protein product 1
electrospray mass spec shows loss of 18 amu from protein
peptide mapping followed by tandem mass spec showed the 18 amu within
the C-terminal tryptic peptide and the final two -DE residues
protein sequencing by Edman degrad. sequencing from N-term of C-term
peptide cannot sequence through the penultimate D residue
Oner hypothesis is that the carboxylic acid groups from the D and E residues
are condensing to form an acid anhydride . The dehydration product appears to
be stable in aqueous buffers at 5-6 pH.
2) Modified protein 2
This may be from the specie above or from the parent
cyclized version of the parent protein in which the C and N termini
react with the loss of the c-term E residue and formation of a peptide bond
between the N-term residue and the penultimate Asp residue.
X-ray crystal structue of the protein show that the N and C are in
Has any one seen such modifications?
Is there an alternate hypothesis to fit the loss of the 18 amu in the last two
Is there another mechanism for cyclization of the protein through the reaction
of the N and C termini that would result in the elimination of the c-term -E
More information about the Proteins