PURIFICATION AND CHARACTERIZATION OF BETA(2)-TOMATINASE, AN ENZYME INVOLVED IN THE DEGRADATION OF ALPHA-TOMATINE AND ISOLATION OF THE GENE ENCODING BETA(2)-TOMATINASE FROM SEPTORIA-LYCOPERSICI
Rw. Sandrock et al., PURIFICATION AND CHARACTERIZATION OF BETA(2)-TOMATINASE, AN ENZYME INVOLVED IN THE DEGRADATION OF ALPHA-TOMATINE AND ISOLATION OF THE GENE ENCODING BETA(2)-TOMATINASE FROM SEPTORIA-LYCOPERSICI, Molecular plant-microbe interactions, 8(6), 1995, pp. 960-970
Lycopersicon species often contain the toxic glycoalkaloid alpha-tomat
ine, which is proposed to protect these plants from general microbial
infection, However, fungal pathogens of tomato often are tolerant to a
lpha-tomatine and detoxification of alpha-tomatine may be how these pa
thogens avoid this potential barrier, As an initial step to evaluate t
his possibility, we have purified to homogeneity a beta-1,2-D glucosid
ase from the tomato pathogen Septoria lycopersici that hydrolyzes the
beta-1,2-D glucosyl bond on the tetrasaccharide moiety of alpha-tomati
ne to produce beta(2)-tomatine. The enzyme is a 110-kDa protein with a
pI of 4.5 and a K-m for alpha-tomatine of 62 mu M, Little or no activ
ity was detected on a variety of other glycosides. The gene encoding t
his protein was isolated and contains an open reading frame of 803 ami
no acids that shares sequence homology with several other beta-D-gluco
sidases. When S. lycopersici was incubated with alpha-tomatine, beta(2
)-tomatinase mRNA accumulated, suggesting that the enzyme is substrate
inducible, Aspergillus nidulans expressed ''beta(2)-tomatinase'' acti
vity when transformed with this gene but transformants were still sens
itive to alpha-tomatine.