Musarmins: three single-chain ribosome-inactivating protein isoforms from bulbs of Muscari armeniacum L. and Miller.
Three new ribosome-inactivating protein (RIP; EC 3.2.2.22) isoforms that we have named musarmins (MUs) 1, 2 and 3 have been isolated from the bulbs of Muscari armeniacum L. and Miller by ion-exchange chromatography and gel filtration. Analysis by electrophoresis revealed that they are single-chain proteins and mass spectrometry analysis afforded Mr values of 28,708, 30,003 and 27,626 for MUs 1, 2 and 3, respectively. Musarmins strongly inhibited protein synthesis carried out by mammalian ribosomes, with IC50 values in the 0.14-0.24nM range but not that carried out by plant cell-free systems or HeLa cells. MUs promote the single depurination of rabbit reticulocyte 28S rRNA. cDNA cloning of genes coding for musarmins revealed that they contain open reading frames of 298, 294 and 295 aminoacids for MU1, MU2 and MU3, respectively. Mature MU1, MU2 and MU3 contain 277, 273 and 273 aminoacids, respectively suggesting post-translational C-terminal processing. An untranslated mRNA coding for an ORF very similar to that of MU3 was detected in leaves. Each of the four MU genes contains an intron. In contrast to other RIPs, MUs are present only in bulbs and are not induced in leaves either by senescence, or by treatment of leaves with H2O2 or salicylic acid, or by growth in darkness. Therefore, these proteins could play a non-vital role in plants; for instance, as anti-pathogens and protective agents only in some stages of the plant life cycle (237).
Arias
F Javier
FJ
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Valladolid, E-47005, Valladolid, Spain.
Antolín
Pilar
P
de Torre
Carlos
C
Barriuso
Begoña
B
Iglesias
Rosario
R
Rojo
M Angeles
MA
Ferreras
J Miguel
JM
Benvenuto
Eugenio
E
Méndez
Enrique
E
Girbés
Tomás
T
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006861:Hydrogen Peroxide / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D019668:Liliaceae / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics; D008969:Molecular Sequence Data; D009699:N-Glycosyl Hydrolases / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology; D010940:Plant Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology; D035281:Plant Tubers / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms; D011500:Protein Synthesis Inhibitors / Q000737:chemistry / Q000494:pharmacology; D011817:Rabbits; D012156:Reticulocytes / Q000187:drug effects; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism; D020156:Salicylic Acid / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid
D010940:Plant Proteins; D020033:Protein Isoforms; D011500:Protein Synthesis Inhibitors; D006861:Hydrogen Peroxide; D009699:N-Glycosyl Hydrolases; D020156:Salicylic Acid