- aff inity ▁dock ing ▁mot ifs . ▁B eta - c aten in ▁contains ▁no ▁such ▁mot ifs , ▁but ▁a ▁special ▁protein ▁does : ▁ax in . ▁What ▁is ▁more , ▁its ▁G SK 3 ▁dock ing ▁mot if ▁is ▁directly ▁adjacent ▁to ▁a ▁ β - c aten in ▁binding ▁mot if . ▁This ▁way , ▁ax in ▁acts ▁as ▁a ▁true ▁sc aff old ▁protein , ▁bringing ▁an ▁en zym e ▁( GS K 3 ) ▁together ▁with ▁its ▁substr ate ▁( β - c aten in ) ▁into ▁close ▁physical ▁proxim ity . ▁ ▁But ▁even ▁ax in ▁does ▁not ▁act ▁alone . ▁Through ▁its ▁N - term inal ▁reg ulator ▁of ▁G - prote in ▁signal ing ▁( R GS ) ▁domain , ▁it ▁rec ruits ▁the ▁ad en om at ous ▁poly pos is ▁col i ▁( AP C ) ▁protein . ▁A PC ▁is ▁like ▁a ▁huge ▁" Christ mas ▁tree ": ▁with ▁a ▁mult itude ▁of ▁ β - c aten in ▁binding ▁mot ifs ▁( one ▁A PC ▁mole c ule ▁alone ▁poss esses ▁ 1 1 ▁such ▁mot ifs ▁), ▁it ▁may ▁collect ▁as ▁many ▁ β - c aten in ▁mole cules ▁as ▁possible . ▁A PC ▁can ▁interact ▁with ▁multiple ▁ax in ▁mole cules ▁at ▁the ▁same ▁time ▁as ▁it ▁has ▁three ▁SA MP ▁mot ifs ▁( Ser - A la - Met - Pro ) ▁to ▁bind ▁the ▁R GS ▁domains ▁found ▁in ▁ax in . ▁In ▁addition ,