ProtSeq
RLNiece@AOL.com
Fri, 12 Sep 1997 23:57:03 -0400 (EDT)
One of our user groups brought us a sample of carbodiimide cross-linked
proteins (A and B, both sequences known) that had then been subsequently
reduced, alkylated and digested with trypsin. The mass of one of the HPLC
peaks indicated it could contain cross-linked peptides from proteins A and B
so we chose to sequence this fraction. In each cycle we saw residues that
fit a peptide from protein A and residues that fit a peptide from protein B.
That was nice. However, while both peptides had several acidic residues,
neither peptide had an internal lysine. Peptide (25 residues long) from A
also had histidine, methionine, tyrosine, serine and threonine; peptide (70
residues long) from B had cysteine, tryptophan, histidine, methionine,
tyrosine, serine and threonine. Of course, both had amino acids like
glycine, alanine and amides. The question is what other reactions might
occur in the presence of carbodiimide that cross-links these two peptides.
It will take more than the 5 pMol of this product that we have to find the
site of cross-linking. Thanks for considering this problem.