x C ▁found ▁in ▁S . ▁a ure us ). ▁Es x A ▁and ▁Es x B ▁belong ▁to ▁a ▁super family ▁of ▁W X G 1 0 0 ▁prote ins ▁that ▁form ▁dim er ic ▁hel ical ▁hair p ins . ▁In ▁S . ▁a ure us , ▁T 7 SS ▁secre tes ▁a ▁large ▁to x in ▁called ▁Es a D , ▁which ▁is ▁a ▁member ▁of ▁nuc lease ▁en zym es . ▁Es a D ▁is ▁made ▁har ml ess ▁( det ox ified ) ▁during ▁its ▁b ios yn thesis ▁with ▁the ▁help ▁of ▁its ▁counter part ▁ant ito x in ▁Es a G . ▁The ▁Es a D - E sa G ▁complex ▁then ▁bind s ▁with ▁Es a E . ▁The ▁Es a E ▁portion ▁bind s ▁to ▁Ess C , ▁which ▁is ▁the ▁an ▁en zym e ▁ATP ase ▁of ▁the ▁T 7 SS ▁complex . ▁During ▁secret ion , ▁Es a G ▁is ▁left ▁in ▁the ▁cy top las m , ▁and ▁only ▁Es a D ▁and ▁Es a E ▁are ▁secret ed ▁together . ▁But ▁in ▁some ▁stra ins ▁of ▁S . ▁a ure us , ▁Es a D ▁is ▁not ▁produced , ▁but ▁two ▁copies ▁of ▁Es a G - like ▁prote ins ▁are ▁formed ▁instead . ▁This ▁might ▁explain ▁the ▁occurrence ▁of ▁T 7 SS ▁in ▁non - path ogen ic ▁species ▁such ▁as ▁B . ▁sub til is ▁and ▁S . ▁co el icol or . ▁ ▁Type ▁IX ▁▁ ▁Type