Source Year: 2002

The lutoid body (bottom) fraction of latex from the rubber tree (H. brasiliensis) contains a limited number of major proteins. These are the chitiin-binding protein hevein, its precursor and C-terminal fragment of the precursor, a basic chitinase/lysozyme, and a B-1, 3-glucanase. The content and properties of the latter enzyme differ between lutoid-body fractions from different rubber clones (PR 261, GT.1, LCB 1320 and PRIM 600). While the enzyme from clone GT.1 is a glycoproteiin with carbohydrate attached to two glycosylation sites, the enzymes from other clones contain little or no carbohydrate. Latex from clone GT.1 has a higher B-1,3-glucanase content than those fron the other three clones, but with a significantly lower specific activity. The enzyme exhibits a pH optimum at 4.5, but there is a second one at 6.7. Peptides isolated from B-1,3-glucanase of clone GT.1 showed that the enzyme is heterogeneous at the C-terminus, probably as a result of removal of a vacuolar targeting sequence by an endopeptidase, followed by further removal of C-terminal residues by a carboxypeptidase-like activity. This incomplete digestion can be related to glycosylation at the extreme C-terminus of the mature enzyme. Non-glycosylated H. brasiliensis B-1,3-glucanases exhibit less C-terminal heterogeneity. A homologue of the antifungal protein osmotin was isolated from rubber clones which are less susceptible to fungal diseases. Another identified protein is identical to a citrate binding proteiin (CBP), already sequenced as cDNA, but with cleaved-off N-terminal signal and C-terminal vacuolar targeting peptides. Four C-terminal propeptides of vacuolar proteins in H. brasiliensis are positively identified, which is a valuable contribution to previously known examplles of this type of processing.