Specific interaction of the tetragonally arrayed protein layer of Bacillus sphaericus with its peptidoglycan sacculus

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Abstract
Tetragonal layer protein (T-layer) isolated from B. sphaericus NTCC 9602 (wild type) or 9602 Lmw (variant) bonded specifically to the sacculi (peptidoglycan) of either cell type. Only uncleaved T-layer subunits were capable of specific recognition of the B. sphaericus sacculi; other Bacillus strains and gram positive bacterial sacculi would not adsorb B. sphaericus strain 9602 T-layer. The peptidoglycan did not function as a template since isolated T-layer subunits self-assembled into characteristic patterns. Upon reassociation with sacculi, T-layer assemblies were randomly oriented patches compared with the more continuous strictly oriented pattern on cells or fresh cell walls. T-layer associated with the sacculus was less susceptible to conditions that dissociated in vitro-assembled T-layer. Mild proteolysis of both wild-type and variant T-layer subunits by a variety of enzymes reduced the MW by 18,000 in all cases, indicating that 1 region of the molecule was particularly susceptible to cleavage. Subunits from which the minor fragment were cleaved upon aging retained the capacity to assemble in vitro, but would no longer adsorb to sacculi. Thus, the ability of T-layer to form networks was separate from its ability to bind to cell walls and the 18,000-dalton piece of the T-layer polypeptide was necessary for attachment to the cell wall.