Abstract
Methanococcus maripaludis is an archaeon with two studied surface appendages, archaella and type IV-like pili. Previously, the major structural pilin was identified as MMP1685 and three additional proteins were designated as minor pilins (EpdA, EpdB and EpdC). All of the proteins are likely processed by the pilin-specific prepilin peptidase EppA. Six other genes were identified earlier as likely encoding pilin proteins processed also by EppA. In this study, each of the six genes (mmp0528, mmp0600, mmp0601, mmp0709, mmp0903 and mmp1283) was deleted and the mutants examined by electron microscopy to determine their essentiality for pili formation. While mRNA transcripts of all genes were detected by RT-PCR, only the deletion of mmp1283 led to nonpiliated cells. This strain could be complemented back to a piliated state by supplying a wildtype copy of the mmp1283 gene in trans. This study adds to the complexity of the type IV pili system in M. maripaludis and raises questions about the functions of the remaining five pilin-like genes and whether M. maripaludis under other growth conditions may be able to assemble additional pili-like structures.
Highlights
Type IV pili are a very common type of surface appendage found in a variety of Gram-negative and Gram positive bacteria, as well as certain members of the Domain Archaea [1,2,3,4,5,6]
MMP1685 is known to be a glycoprotein with an attached N-linked pentasaccharide identical in structure to the tetrasaccharide identified attached to archaellins [58] but with an additional hexose attached as a branch to the linking sugar Nacetyl-galactosamine [31]
Methanococcus maripaludis is known to have at least two surface appendages that are assembled in a bacterial type IV pili mode, namely archaella and type IV-like pili [3,26,62]
Summary
Type IV pili are a very common type of surface appendage found in a variety of Gram-negative and Gram positive bacteria, as well as certain members of the Domain Archaea [1,2,3,4,5,6]. The conserved inner membrane or platform protein is considered to interact with the ATPase(s) and form an export complex for the structural proteins and to be involved in both pilus assembly and disassembly [10]. In addition to these conserved components, type IV pili systems in different organisms often have other components whose role in pilus assembly and function remain unknown [6]
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