De novo sequencing and disulfide mapping of a bromotryptophan-containing conotoxin by Fourier transform ion cyclotron resonance mass spectrometry.
T-1-family conotoxins belong to the T-superfamily and are composed of 10-17 amino acids. They share a common cysteine framework and disulfide connectivity and exhibit unusual posttranslational modifications, such as tryptophan bromination, glutamic acid carboxylation, and threonine glycosylation. We have isolated and characterized a novel peptide, Mo1274, containing 11 amino acids, that shows the same cysteine pattern, -CC-CC, and disulfide linkage as those of the T-1-family members. The complete sequence, GNWCCSARVCC, in which W denotes bromotryptophan, was derived from MS-based de novo sequencing. The FT-ICR MS/MS techniques of electron capture dissociation (ECD), infrared multiphoton dissociation, and collision-induced dissociation served to detect and localize the tryptophan bromination. The bromine contributes a distinctive isotopic distribution in all fragments that contain bromotryptophan. ECD fragmentation results in the loss of bromine and return to the normal isotopic distribution. Disulfide connectivity of Mo1274, between cysteine pairs 1-3 and 2-4, was determined by mass spectrometry in combination with chemical derivatization employing tris(2-carboxyethyl)phosphine, followed by differential alkylation with N-ethylmaleimide and iodoacetamide. The ECD spectra of the native and partially modified peptide reveal a loss of bromine in a process that requires the presence of a disulfide bond.
Nair
Sudarslal Sadasivan
SS
National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, FL 32310-4005, USA.
Nilsson
Carol L
CL
Emmett
Mark R
MR
Schaub
Tanner M
TM
Gowd
Konkallu Hanumae
KH
Thakur
Suman S
SS
Krishnan
K S
KS
Balaram
Padmanabhan
P
Marshall
Alan G
AG
D000595:Amino Acid Sequence; D001965:Bromides / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D020916:Conotoxins / Q000032:analysis* / Q000737:chemistry*; D004220:Disulfides / Q000032:analysis* / Q000737:chemistry*; D013058:Mass Spectrometry; D010455:Peptides / Q000737:chemistry / Q000302:isolation & purification; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D014364:Tryptophan / Q000032:analysis / Q000737:chemistry*
D001965:Bromides; D020916:Conotoxins; D004220:Disulfides; D010455:Peptides; D014364:Tryptophan