Determination of the post-translational modifications of salivary acidic proline-rich proteins.
Human salivary acidic proline-rich proteins were analyzed by electrospray-ion trap mass spectrometry and by matrix-assisted laser desorption/ionization-time of flight mass spectrometry. All acidic-PRP isoforms share a common N-terminal region, which contains a pyroglutamic acid residue at the N-terminus, and two phosphorylation sites on Ser 8 and 22. At the same time, HPLC-MS spectra revealed isoforms of PRP-1 and PRP-3 having a different number of phosphoserine residues, namely, a mono-phosphorylated form of PRP-1 and PRP-3 and a tri-phosphorylated form of PRP-1. The analysis of the masses of tryptic digests suggested that the third phosphate residue should be located on Ser 17. Another protein with a mass of 30,923 amu was detected along the HPLC pattern and MS data of its tryptic digest suggested that it corresponds to the dimer of Pa, the isoform of PRP-1 with a substitution Arg-Cys at 103 position. Finally, structural identification is pending for another post-translational modification of acidic-PRP that provides an increase of 111-114 amu.
Castagnola
M
M
Institute of Biochemistry and Clinical Biochemistry, Catholic University of Rome, Rome, Italy. massimo.castagnola@icrm.cnr.it
Cabras
T
T
Inzitari
R
R
Zuppi
C
C
Rossetti
D V
DV
Petruzzelli
R
R
Vitali
A
A
Loy
F
F
Conti
G
G
Fadda
M B
MB
D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D013058:Mass Spectrometry; D008970:Molecular Weight; D010455:Peptides / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D010766:Phosphorylation; D011392:Proline / Q000737:chemistry; D020033:Protein Isoforms / Q000737:chemistry; D011499:Protein Processing, Post-Translational; D011761:Pyrrolidonecarboxylic Acid / Q000737:chemistry; D012471:Salivary Proteins and Peptides / Q000737:chemistry* / Q000187:drug effects; D012694:Serine / Q000737:chemistry / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014357:Trypsin / Q000378:metabolism
D010455:Peptides; D020033:Protein Isoforms; D012471:Salivary Proteins and Peptides; D012694:Serine; D011392:Proline; D014357:Trypsin; D011761:Pyrrolidonecarboxylic Acid