title: Protein circlets as sex pilus subunits.
abstract: The largest circular protein structures discovered define a class of transfer proteins acting in bacterial conjugation and type IV secretion. Proteins ranging from 73 to 78 residues with head-to-tail peptide bonds constitute the major subunit of conjugative pili of some type IV secretion systems. Their plasmid-encoded precursors are enzymatically processed and cyclized before being assembled into pili. These extra-cellular surface filaments mediate physical contact between donor and recipient cell or pathogen and host cell. Pili are essential prerequisites for DNA and protein transfer. A membrane-bound signal peptidase-like enzyme is responsible for the circularization reaction. Site-directed mutagenesis and mass spectrometry has been used extensively to unravel the mechanism of the enzyme-substrate interaction of the pilin maturation process.
authors.affiliation: Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA.
authors.forename: Markus
authors.initials: M
authors.lastname: Kalkum
authors.forename: Ralf
authors.initials: R
authors.lastname: Eisenbrandt
authors.forename: Erich
authors.initials: E
authors.lastname: Lanka
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003500:Cyclization; D006801:Humans; D008969:Molecular Sequence Data; D018933:Pili, Sex / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D011499:Protein Processing, Post-Translational; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D021122:Protein Subunits