Cyclization of N-terminal S-carbamoylmethylcysteine causing loss of 17 Da from peptides and extra peaks in peptide maps.
Enzymatic digests of proteins S-alkylated with iodoacetamide may contain peptides with N-terminal S-carbamoylmethylcysteine. These can be partly converted to a form with 17 Da lower mass and increased HPLC retention. Proof by synthesis supported by MS/MS and NMR spectroscopy was used to show that N-terminal S-carbamoylmethyl-L-cysteine can cyclize, losing NH3 to form an N-terminal residue of (R)-5-oxoperhydro-1,4-thiazine-3-carboxylic acid. The abbreviation Otc is proposed for the (R)-5-oxoperhydro-1,4-thiazine-3-carbonyl residue. The rate of cyclization is significant in 0.1 M NH4HCO3 at 37 degrees C, with the half-life of the acyclic form being 10-12 h for several peptides tested. This is similar to the rate at which N-terminal pyroglutamate forms from N-terminal glutamine.
Geoghegan
Kieran F
KF
Pfizer Global Research and Development, Eastern Point Road, Groton, Connecticut 06340, USA. kieran_f_geoghegan@groton.pfizer.com
Hoth
Lise R
LR
Tan
Douglas H
DH
Borzilleri
Kris A
KA
Withka
Jane M
JM
Boyd
James G
JG
D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000031:analogs & derivatives*; D007460:Iodoacetamide / Q000378:metabolism; D013058:Mass Spectrometry; D010455:Peptides / Q000032:analysis* / Q000378:metabolism; D010456:Peptides, Cyclic / Q000032:analysis / Q000138:chemical synthesis* / Q000378:metabolism
D010455:Peptides; D010456:Peptides, Cyclic; D003545:Cysteine; D007460:Iodoacetamide