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S層(: S-layer)とは一般に真正細菌古細菌に認められる細胞外皮(en:cell envelope)の一部位。S層はタンパク質あるいは糖タンパク質から構成される単分子層である。S層の二次元構造は自己組織化を経て形成され、細胞表面を囲む。S層のタンパク質は細胞のタンパク質量の10-15%を占める。 [1] [2] [3].

S層のタンパク質はほとんど保存されておらず、種差が大きい。S層の厚さは種により5-25nmの厚さであり、直径2-8nmの均一な微細孔がある。 [4]. S-layers exhibit either an oblique (p1, p2), square (p4) or hexagonal (p3, p6) lattice symmetry. Depending on the lattice symmetry the S-layer is composed of one (P1), two (P2), three (P3), four (P4) or six (P6) identical protein subunits, respectively. The centre to centre spacings (or unit cell dimensions) between these subunits range between 2.5 and 35 nm.


  • In Gram-negative bacteria S-layers are associated to the LPS via ionic, carbohydrate-carbohydrate, protein carbohydrate interactions and/or protein-protein interactions.
  • In Gram-positive bacteria whose S-layers contain surface layer homology (SLH) domains the binding occurs to the peptidoglycan and to a secondary cell wall polymer (e.g. teichuronic acids). In the absence of SLH domains the binding occurs via electrostatic interactions between the positively charged N-terminus of the S-layer protein and a negatively charged secondary cell wall polymer.
  • In Gram-negative archaea S-layer proteins possess a hydrophobic anchor that is associated with the underlying lipid membrane.
  • In Gram-positive archaea the S-layer proteins bind pseudomurein or to methanochondritin.



  • バクテリオファージ食作用に対する防御
  • 低pHに対する耐性
  • 高分子物質(溶菌酵素など)に対する障壁
  • 接着(for glycosylated S-layers)
  • 膜の安定化
  • provide adhesion sites for exoproteins
  • provide a periplasmic compartment in Gram-positive prokaryotes together with the peptidoglycan and the cytoplasmic membrane


  1. ^ Messner P, Sleytr U (1992). “Crystalline bacterial cell-surface layers”. Adv. Microb. Physiol. 33: 213-75. PMID 1636510. 
  2. ^ Pum D, Messner P, Sleytr U (1991). “Role of the S layer in morphogenesis and cell division of the archaebacterium Methanocorpusculum sinense”. J. Bacteriol. 173 (21): 6865-73. PMID 1938891. 
  3. ^ Sleytr U, Messner P, Pum D, Sára M (1993). “Crystalline bacterial cell surface layers”. Mol. Microbiol. 10 (5): 911-6. doi:10.1111/j.1365-2958.1993.tb00962.x. PMID 7934867. 
  4. ^ Sleytr U, Bayley H, Sára M, Breitwieser A, Küpcü S, Mader C, Weigert S, Unger F, Messner P, Jahn-Schmid B, Schuster B, Pum D, Douglas K, Clark N, Moore J, Winningham T, Levy S, Frithsen I, Pankovc J, Beale P, Gillis H, Choutov D, Martin K (1997). “Applications of S-layers”. FEMS Microbiol. Rev. 20 (1-2): 151-75. PMID 9276930.