Crystal structure of a PP2A B56-BubR1 complex and its implications for PP2A substrate recruitment and localization

Protein phosphatase 2A （PP2A） accounts for the majority of total Ser/Thr phosphatase activities in most cell types and regulates many biological processes. PP2A holoenzymes contain a scaffold A subunit, a cat- alytic C subunit, and one of the regulatory/targeting B subunits. How the B subunit controls PP2A localization and substrate specificity, which is a crucial aspect of PP2A regulation, remains poorly understood. The kine- tochore is a critical site for PP2A functioning, where PP2A orchestrates chromosome segregation through its interactions with BubR1. The PP2A-BubR1 interac- tion plays important roles in both spindle checkpoint silencing and stable microtubule-kinetochore attach- ment. Here we present the crystal structure of a PP2A B56-BubRI complex, which demonstrates that a con- served BubRl LxxlxE motif binds to the concave side of the B56 pseudo-HEAT repeats. The BubR1 motif binds to a groove formed between B56 HEAT repeats 3 and 4, which is quite distant from the B56 binding surface for PP2A catalytic C subunit and thus is unlikely to affect PP2A activity. In addition, the BubR1 binding site on B56 is far from the B56 binding site of shugoshin, another kinetochore PP2A-binding protein, and thus BubR1 and shugoshin can potentially interact with PP2A-B56 simultaneously. Our structural and biochemical analysis indicates that other proteins with the LxxlxE motif may also bind to the same PP2A B56 surface. Thus, our structure of the PP2A B56-BubR1 complex provides important insights into how the B56 subunit directs the recruitment of PP2A to specific targets.

FLOWERING PLANTS AND ENTOMOPHAGOUS ARTHROPODS IN THE AGRICULTURAL LANDSCAPE: A PRACTISE-ORIENTED SUMMARY OF A COMPLEX RELATIONSHIP

There is a growing demand for high-quality agricultural products and morecountries have adopted landscape management by sowing flowering plants inagricultural fields as an important branch of conservation biological control.However, there has been less concern over the interactions and trade-offsbetween floral plants and entomophagous arthropods. This paper reviewprogress in pollen/nectar feeding habits of entomophagous insects includingparasitoids and predators which are important natural enemies of crop pestsin agricultural fields. Factors that influence the preference of different guilds of natural enemies are reviewed to guide the selection of flowering plants inconservation biological control practices. Most studies find that floralresources have positive effects on both biological traits of natural enemies andtheir abundance and diversity, and this is believed to contribute greatly to pestcontrol. Furthermore, the potential impacts of floral resources on crop yieldsare also discussed with an emphasis on a guild of entomophagous insects thatprovides both pest control and pollination services.