A cascade of 24 histatins (histatin 3 fragments) in human saliva. Suggestions for a pre-secretory sequential cleavage pathway.
The systematic search by tandem mass spectrometry of human saliva from four different subjects, of 136 possible fragments originated from histatin 3, allowed the detection of 24 different peptides. They include, with the exception of histatin 4, all the known histatin 3 fragments, namely histatins 5-12 and the peptides corresponding to 15-24, 26-32, 29-32 residues, and 13 new fragments corresponding to 1-11, 1-12, 1-13, 5-13, 6-11, 6-13, 7-11, 7-12, 7-13, 14-24, 14-25, 15-25, and 28-32 residues of histatin 3. On the contrary, none of 119 possible fragments of histatin 1, including histatin 2, was detected. The results suggest that the genesis of histatin 3-related peptides, being under the principal action of trypsin-like activities, is probably not a random process but rather follows a sequential fragmentation pathway. Lack of detection of C-terminal fragments, with the exception of 26-32, 28-32, and 29-32 fragments, suggested that arginine 25 should be the first cleavage site, generating histatin 6 and 26-32 fragments. The genesis of 28-32 and 29-32 fragments and histatin 5 should implicate a subsequent exo-protease action. Similarly, lack of detection of fragments having Lys-5 and Arg-6 at the N terminus and Arg-25 at the C terminus strongly suggested that sequences KRKF (11-14 residues) and AKR (4-6 residues) should be the second and the third cleavage sites, respectively. Lys-17 and Arg-22 are not cleaved at all.
Istituto di Biochimica e Biochimica Clinica, Facoltà di Medicina, Università Cattolica, Roma, Italy. massimo.castagnola@icrm.cnr.it
Massimo
M
Castagnola
Rosanna
R
Inzitari
Diana Valeria
DV
Rossetti
Chiara
C
Olmi
Tiziana
T
Cabras
Vincenzo
V
Piras
Paola
P
Nicolussi
Maria Teresa
MT
Sanna
Mariagiuseppina
M
Pellegrini
Bruno
B
Giardina
Irene
I
Messana
D000595:Amino Acid Sequence; D001665:Binding Sites; D010450:Endopeptidases / Q000378:metabolism; D054808:Histatins; D006801:Humans; D013058:Mass Spectrometry; D010446:Peptide Fragments / Q000032:analysis*; D011506:Proteins / Q000032:analysis; D012463:Saliva / Q000737:chemistry; D012471:Salivary Proteins and Peptides / Q000032:analysis*; D000099053:Histidine-Rich Glycoprotein
C068075:HTN3 protein, human; D054808:Histatins; D010446:Peptide Fragments; D011506:Proteins; D012471:Salivary Proteins and Peptides; D000099053:Histidine-Rich Glycoprotein; D010450:Endopeptidases