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）是一种负责通过降解果皮细胞壁中的β-（1，4）-半乳聚糖来软化果实的酶。为了获得对底物特异性的结构洞察，我们确定了TBG4及其与β-D-半乳糖的复合物的晶体结构。TBG4由催化TIM桶结构域和随后的三个β-夹心结构域组成。此外，我们还对TBG1的酶学性质和底物特异性进行了研究。TBG4对β-（1，4）-连接有底物识别作用，而TBG1对β-（1，3）和β-（1，6）-连接有底物识别作用，说明TBG在番茄果实发育成熟过程中作用于细胞壁，成熟期番茄果实细胞壁以糖为底物进行构建/重构。

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.