Structural based fruit softening mechanism; the model of tomato fruit softening during maturation

在番茄果实中，β -半乳糖苷酶4 （TBG4）是一种通过降解果皮细胞壁中的β -(1,4)-半乳糖来使果实软化的酶。为了深入了解底物特异性，我们测定了TBG4及其与β - d -半乳糖配合物的晶体结构。TBG4由一个催化TIM桶状结构域和三个β -三明治结构域组成。该结构与GH35家族的其他β -半乳糖苷酶相似。此外，我们还测定了TBG1的酶学性质和底物特异性。TBG4具有对β -(1,4)-连锁的底物识别，然而TBG1具有β -(1,3)和β -(1,6)-类底物。结果表明，在番茄果实发育和成熟过程中，TBG对番茄细胞壁有一定的作用，并且在番茄果实细胞壁的几个阶段，糖作为底物对TBG起作用。

In tomato fruit, beta-galactosidase 4 (TBG4) is an enzyme responsible for fruit softening through the degradation of beta-(1,4)-galactan in the pericarp cell wall. To gain structural insight into the substrate specificity, we determined the crystal structures of TBG4 and its complex with beta-D-galactose. TBG4 was composed of a catalytic TIM barrel domain followed by three beta-sandwich domains. This structure is similar to other beta-galactosidase belong to GH35 families.In addition, we determined the enzymatic properties and substrate specificities of TBG1. TBG4 has substrate recognition to beta-(1,4)-linkage, however, TBG1 has beta-(1,3) and beta-(1,6)-likage substrate.In these results, TBG's act on the tomato cell wall during fruits development and maturation, and seberal stage of tomato fruits cell walls construct/reconstruct to some components sugar as a substrate against TBG's.