Cell wall of Thermoanaerobacterium thermosulfurigenes EM1: isolation of its components and attachment of the xylanase XynA

Thermoanaerobacterium thermosulfurigenes EMI has a gram-positive type cell wall completely covered by a surface layer (S-layer) with hexagonal lattice symmetry. The components of the cell envelope were isolated, and the S-lay er protein was purified and characterized. S-layer monomers assembled in vi tro into sheets with the same hexagonal symmetry as in vivo. Monosaccharide analysis revealed that the S-layer is associated with fucose, rhamnose, ma nnosamine, glucosamine, galactose, and glucose. The N-terminal 31 amino aci d residues of the S-layer protein showed significant similarity to SLH (S-l ayer homology) domains found in S-layer proteins of different bacteria and in the exocellular enzymes pullulanase, polygalacturonate hydrolase, and xy lanase of T. thermosulfurigenes EM1. The xylanase from T. thermosulfurigene s EMI was copurified with the Slayer protein during isolation of cell wall components. Since SLH domains of some structural proteins have been shown t o anchor these proteins noncovalently to the cell envelope, we propose a co mmon anchoring mechanism for the S-layer protein and exocellular enzymes vi a their SLH domains in the peptidoglycan-containing layer of T. thermosulfu rigenes EM1.