Evidence for a third structural class of beta-1,3-glucanase in tobacco.
Glucan endo-1,3-beta-glucosidases (beta-1,3-glucanases) have been implicated in several developmental processes and they may also play a direct role in the plant's defense against fungal pathogens. In an effort to characterize the glucanase gene family, complementary DNA clones encoding an acidic form of beta-1,3-glucanase have been isolated from tobacco. The cDNA was expressed in E. coli and shown to encode a beta-1,3-glucanase activity. The protein sequence encoded by the cDNA was found to match the partial protein sequence of PR-35, a previously characterized beta-1,3-glucanase. The protein encoded by the cDNA was purified from the extracellular fluid of TMV-infected tobacco leaves and found by immunological methods to correspond to glucanase PR-Q'. From a detailed analysis of the cDNA it is clear that this glucanase represents a third structural class of enzyme which differs substantially from both the basic, vacuolar glucanase and the acidic, extracellular forms (PR-2, PR-N and PR-O). It has previously been demonstrated that the basic form of beta-1,3-glucanase is synthesized as a pre-pro-enzyme and upon maturation the 21 amino acid signal peptide and a 22 amino acid carboxy-terminal peptide are removed. This processing event has been proposed to be involved with the vacuolar localization of the enzyme. By comparing the deduced protein structure of PR-Q' to that of the basic form it is evident that this extracellular enzyme is missing the carboxy-terminal 22 amino acids. The role of a conserved phenylalanine-glycine dipeptide in the processing of glucanases and other pathogenesis-related proteins from tobacco is discussed.
Payne
G
G
CIBA-GEIGY Agricultural Biotechnology Research Unit, Research Triangle Park, NC 27709.
Ward
E
E
Gaffney
T
T
Goy
P A
PA
Moyer
M
M
Harper
A
A
Meins
F
F
Ryals
J
J
D000595:Amino Acid Sequence; D001483:Base Sequence; D002480:Cellulase / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D002688:Chitinases / Q000235:genetics; D004247:DNA / Q000235:genetics; D005110:Extracellular Space / Q000201:enzymology*; D017343:Genes, Plant; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009029:Mosaic Viruses / Q000502:physiology; D010940:Plant Proteins / Q000096:biosynthesis / Q000235:genetics*; D010947:Plants, Toxic; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000096:biosynthesis; D012689:Sequence Homology, Nucleic Acid; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics*
D010940:Plant Proteins; D011994:Recombinant Proteins; C053376:pathogenesis-related proteins, plant; D004247:DNA; D002688:Chitinases; D002480:Cellulase