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Publication Abstract from PubMed

Conjugative plasmid transfer is the most important means of spreading antibiotic resistance and virulence genes among bacteria and therefore, presents a serious threat to human health. The process requires direct cell-cell contact made possible by a multi-protein complex that spans cellular membranes and serves as a channel for macromolecular secretion. Thus far, well studied conjugative T4SS are of G- origin. Although many medically relevant pathogens (e.g. enterococci, staphylococci, streptococci) are G+, their conjugation systems have received little attention. This study provides structural information for the transfer protein TraM of the G+ broad-host range Enterococcus conjugative plasmid pIP501. Immuno-localization demonstrated that the protein localizes to the cell wall. We then used opsonophagocytosis (OPA) as a novel tool to verify that TraM was exposed on the cell surface. In these assays antibodies generated to TraM recruited macrophages and enabled killing of pIP501 harboring E. faecalis cells. The crystal structure of the C-terminal, surface exposed domain of TraM was determined to 2.5 A resolution. The structure, molecular dynamics and cross-linking studies indicated that a TraM trimer acts as the biological unit. Despite the absence of sequence-based similarity, TraM unexpectedly displayed a fold similar to the T4SS VirB8 proteins from Agrobacterium tumefaciens and Brucella suis (G-) and to the transfer protein TcpC from Clostridium perfringens plasmid pCW3 (G+). Based on the alignments of secondary structure elements of VirB8-like proteins from mobile genetic elements and chromosomally encoded T4SS from G+ and G- bacteria, we propose a new classification scheme of VirB8-like proteins.

The 2.5 A Structure of the Enterococcus Conjugation Protein TraM resembles VirB8 Type IV Secretion Proteins.,Goessweiner-Mohr N, Grumet L, Arends K, Pavkov-Keller T, Gruber CC, Gruber K, Birner-Gruenberger R, Kropec-Huebner A, Huebner J, Grohmann E, Keller W J Biol Chem. 2012 Nov 27. PMID:23188825^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.