▁are ▁different ▁from ▁other ▁secret ion ▁systems ▁in ▁that ▁they ▁se crete ▁themselves ▁and ▁only ▁involves ▁the ▁outer ▁cell ▁memb rane . ▁For ▁secret ed ▁protein ▁to ▁pass ▁through ▁the ▁inner ▁cell ▁memb rane , ▁T 5 SS ▁depends ▁on ▁Sec ▁system . ▁They ▁have ▁a ▁ β - bar rel ▁domain , ▁which ▁inser ts ▁into ▁the ▁outer ▁cell ▁memb rane ▁and ▁forms ▁a ▁channel ▁that ▁can ▁transport ▁secret ed ▁protein ▁along ▁with ▁it . ▁For ▁this ▁activity , ▁they ▁are ▁also ▁called ▁the ▁aut otr ans porter ▁systems . ▁When ▁the ▁secret ed ▁prote ins ▁are ▁exposed ▁outside , ▁the ▁aut otr ans por ters ▁are ▁cut ▁off ▁( cle aved ), ▁re le asing ▁the ▁protein ▁from ▁the ▁ β - bar rel ▁domain . ▁An ▁example ▁of ▁aut otr ans porter ▁is ▁the ▁Tr imer ic ▁Aut otr ans porter ▁Ad hes ins . ▁ ▁Type ▁VI ▁▁ ▁Type ▁VI ▁secret ion ▁systems ▁( T 6 SS ) ▁were ▁discovered ▁by ▁the ▁team ▁of ▁John ▁M ek al anos ▁at ▁the ▁Harvard ▁Medical ▁School ▁in ▁ 2 0 0 6 ▁from ▁V ib rio ▁ch ol era e ▁and ▁Pseud omon as ▁aer ugin osa . ▁They ▁were ▁recogn ised ▁when ▁mut ations ▁in ▁the ▁V ib rio ▁Ch ol era e ▁H cp ▁and ▁V rg G ▁gen es ▁caused ▁dimin ished ▁vir ul ence ▁and ▁path ogen icity . ▁In ▁addition ▁to ▁their ▁classic ▁role ▁as ▁the ▁path ogen icity ▁factor , ▁T 6 SS ▁are ▁also