odd modifications
Hawes, John W. (jhawes@iupui.edu)
Fri, 15 Oct 1999 11:54:42 -0500
I have observed some odd peptide modifications by ESI-MS. Would like any
opinions. This is a project where cultured mammalian cells were "fed" a
peptide, to observe binding to a receptor. After binding was observed, the
cells were washed and the peptide was recovered from the receptor and given
to me for structural characterization. Two species were observed with
successive cleavages from the N-terminus as compared to the original
sequence. That was very clear from the mass and from fragmentation. We
also have the same two species each with an odd modification at the amino
terminus. One has N-terminal Val with modification of +14. The other has
N-terminal Asn with modification of -15. For each of these we have a good
series of both b and y ions, so we are confident of the sequences and of
N-terminal modification. I can imagine +14 as methylation. But is
N-terminal methylation probable?, especially in the context of a proteolytic
cleavage. And what could Asn +15 be??? Any ideas? I would give you the
sequence but was requested not to. Any suggestions would be greatly
appreciated. Thanks.
John Hawes
Biochemistry Biotechnology Facility
Indiana University School of Medicine
jhawes@iupui.edu