H ▁ ▁bar rier ▁against ▁high - m ole cular - weight ▁subst ances ▁( e . g ., ▁l yt ic ▁en zym es ) ▁ ▁ad hes ion ▁( for ▁g ly cos yl ated ▁S - layers ) ▁ ▁stabil isation ▁of ▁the ▁memb rane ▁( e . g . ▁the ▁S DBC ▁in ▁De in oc oc cus ▁rad iod ur ans ) ▁▁ ▁resistance ▁against ▁elect romagnet ic ▁stress ▁( e . g . ▁ion izing ▁radi ations ▁and ▁high ▁temper atures ) ▁▁ ▁provision ▁of ▁ad hes ion ▁sites ▁for ▁ex op rote ins ▁ ▁provision ▁of ▁a ▁peri pl asm ic ▁compart ment ▁in ▁Gram - pos itive ▁pro k ary otes ▁together ▁with ▁the ▁pe pt id og ly can ▁and ▁the ▁cy top las mic ▁memb ran es ▁ ▁anti - f ou ling ▁properties ▁ ▁bi om iner al ization ▁ ▁mole cular ▁s ieve ▁and ▁bar rier ▁function ▁ ▁S - layer ▁structure ▁ ▁While ▁u bi quit ous ▁among ▁Arch ae a , ▁and ▁common ▁in ▁b acter ia , ▁the ▁S - layers ▁of ▁diverse ▁organ isms ▁have ▁unique ▁struct ural ▁properties , ▁including ▁symmetry ▁and ▁unit ▁cell ▁dimensions , ▁due ▁to ▁fundamental ▁differences ▁in ▁their ▁constitu ent ▁building ▁blocks . ▁Se quence ▁anal ys es ▁of ▁S - layer ▁prote ins ▁have ▁predicted ▁that ▁S - layer ▁prote ins ▁have ▁sizes ▁of ▁ 4 0 - 2 0 0 ▁k Da ▁and ▁may ▁be ▁composed ▁of ▁multiple ▁domains ▁some