Post-translational modification of bovine pro-opiomelanocortin. Tyrosine sulfation and pyroglutamate formation, a mass spectrometric study.
The amino-terminal fragment of beta-lipotropin (i.e. beta-lipotropin (1-40)) and joining peptide portions of pro-opiomelanocortin have been purified from extracts of bovine posterior pituitaries. Peptides were purified using a combination of reversed-phase and ion-exchange batch extraction procedures followed by reversed-phase high performance liquid chromatography. beta-Lipotropin (1-40) was found to consist of four major components while joining peptide was found to consist of two major components. Fast atom bombardment-mass spectrometric analysis of the tryptic fragments of both peptides revealed that the observed heterogeneity could be explained in terms of post-translational modifications. beta-Lipotropin (1-40) was found to be sulfated at tyrosine residue 28 to an extent of about 50%. The tyrosine residue in beta-lipotropin (1-40) is situated within an amino acid sequence with a preponderance of glutamate residues. Sulfation of this amino acid residue is entirely compatible with the known primary structure requirements of the sulfotransferase enzyme located in the trans-Golgi fraction. Both beta-lipotropin (1-40) and joining peptide were found to have pyroglutamate at their amino termini to an extent of about 50%. The cDNA sequence for bovine pro-opiomelanocortin predicts the presence of glutamic acid at position 1 of both peptides. Pyroglutamate is normally formed through the cyclization of glutamine. This reaction is thought to be catalyzed by a pyroglutamate forming enzyme located within the secretory granule fraction. Under certain circumstances peptides with glutamate at their amino termini may act as substrates for this enzyme.
Bateman
A
A
Endocrine Laboratory, Royal Victoria Hospital, Montreal, Quebec, Canada.
Solomon
S
S
Bennett
H P
HP
D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D013058:Mass Spectrometry / Q000379:methods; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000302:isolation & purification; D011333:Pro-Opiomelanocortin / Q000737:chemistry / Q000235:genetics*; D011499:Protein Processing, Post-Translational; D011761:Pyrrolidonecarboxylic Acid / Q000032:analysis*; D013431:Sulfates / Q000032:analysis; D014443:Tyrosine; D008083:beta-Lipotropin / Q000737:chemistry / Q000235:genetics*
D010446:Peptide Fragments; D013431:Sulfates; D014443:Tyrosine; D011333:Pro-Opiomelanocortin; D008083:beta-Lipotropin; D011761:Pyrrolidonecarboxylic Acid