Organization of K88ac-encoded polypeptides in the Escherichia coli cell envelope: Use of minicells and outer membrane protein mutants for studying assembly of pili

E. coli K-12 minicells, harboring recombinant plasmids encoding polypeptides involved in the expression K88ac adhesion pili on the bacterial cell surface, were labeled with [³⁵S] methionine and fractionated by a variety of techniques. A 70,000-dalton polypeptides, the product of K88ac adhesion cistron adhA, was primarily located in the outer membrane of minicells, although it was less clearly associated with this membrane than the clasical outer membrane protein OmpA and matrix protein. Two polypeptides of molecular weights 26,000 and 17,000 (the products of adhB and adhC, respectively) were located in significant amounts in the periplasmic space. The 29,000-dalton polypeptide was shown to be processed in E.coli minicells. The 23,500-dalton K88ac pilus subunit (the product of adhD) was detected in both inner and outer membrane fractions. E. coli mutants defective in the synthesis of murein lipoprotein or the major outer membrane polypeptide OmpA were found to express normal amounts of K88ac antigen on the cell surface, whereas expression of the K88ac antigen was greatly reduced in perA mutants. The possible functions of the adh cistron products are discussed.