BACTERIAL S-LAYERS

S-layers are paracrystalline planar assemblies of protein (or glycopro tein) which coat the surfaces of some gram-negative and gram-positive bacteria (eubacteria) and archaea (archaeobacteria). Over the past thr ee to tour years, high resolution three-dimensional structures of seve ral S-layers have been obtained by transmission electron microscopy an d, now, scanning probe microscopy (both atomic force and scanning tunn eling microscopies) is providing topographical detail. Molecular appro aches on select S-layer producing bacteria are helping to define the s ynthetic and translocative pathways necessary before surface self-asse mbly can commence. In an industrial sense, S-layers are contributing t o a new application science, nanotechnology, where they are being used as molecular filters, immobilization and affinity matrices, and biose nsors.