Novel Archaeal Adhesion Pilins with a Conserved N Terminus

Abstract

Type IV pili play important roles in a wide array of processes, including surface adhesion and twitching motility. Although archaeal genomes encode a diverse set of type IV pilus subunits, the functions for most remain unknown. We have now characterized six Haloferax volcanii pilins, PilA[1-6], each containing an identical 30-amino-acid N-terminal hydrophobic motif that is part of a larger highly conserved domain of unknown function (Duf1628). Deletion mutants lacking up to five of the six pilin genes display no significant adhesion defects; however, H. volcanii lacking all six pilins (⌬pilA[1-6]) does not adhere to glass or plastic. Consistent with these results, the expression of any one of these pilins in trans is sufficient to produce functional pili in the ⌬pilA[1-6] strain. PilA1His and PilA2His only partially rescue this phenotype, whereas ⌬pilA[1-6] strains expressing PilA3His or PilA4His adhere even more strongly than the parental strain. Most surprisingly, expressing either PilA5His or PilA6His in the ⌬pilA[1-6] strain results in microcolony formation. A hybrid protein in which the conserved N terminus of the mature PilA1His is replaced with the corresponding N domain of FlgA1 is processed by the prepilin peptidase, but it does not assemble functional pili, leading us to conclude that Duf1628 can be annotated as the N terminus of archaeal PilA adhesion pilins. Finally, the pilin prediction program, FlaFind, which was trained primarily on archaeal flagellin sequences, was successfully refined to more accurately predict pilins based on the in vivo verification of PilA[1-6].

The Geoglobus acetivorans Genome: Fe(III) Reduction, Acetate Utilization, Autotrophic Growth, and Degradation of Aromatic Compounds in a Hyperthermophilic Archaeon

“…A local BLAST search against a set of all archaeal sequences assigned as "pilins" in the Uniprot database on 4 July 2014 revealed that the three FlaFind-positive proteins of G. acetivorans are related to archaeal pilins. One protein is Gace_2010, which shares homology with the PilA major structural pilin of a haloarchaeon (Natronomonas pharaonis) and possesses a characteristic N-terminal hydrophobic motif belonging to the Duf1628 domain, recently identified in adhesion pilins of Haloferax volcanii (39). Another putative component of the G. acetivorans pilus structure is encoded by Gace_2093, which shares weak similarity with proteins involved in flagellin/pilin biosynthesis (40).…”

“…In addition to fla genes, several pilins have been predicted with the FlaFind 1.2 online service (39). The FlaFind search retrieved 19 sequences in the genome of G. acetivorans, two of which encode the FlaB structural flagellin (Gace_0653, 0654).…”

Antarctic archaea–virus interactions: metaproteome-led analysis of invasion, evasion and adaptation

“…Adhesin and other predicted cell surface proteins Adhesins are cell surface proteins containing adhesion domains and are involved in cell attachment (for example, pili; Esquivel et al, 2013). Two tADL adhesin variants were detected in the metaproteome with 66% and 33% identity to haltADL_1387 and halTADL_1885, respectively.…”

A conserved type IV pilin signal peptide H‐domain is critical for the post‐translational regulation of flagella‐dependent motility

“…For instance, flagella are required for the swimming motility of planktonic cells and enhance initial type IV pilus-dependent attachment of many bacteria and archaea to surfaces (O'Toole and Kolter, 1998;Ghosh and Albers, 2011). However, flagella are not required, and indeed hinder, subsequent stages of biofilm development whereas adhesive pili are crucial to the formation of cell aggregates in many prokaryotic biofilms (Fröls et al, 2008;Karatan and Watnick, 2009;Pohlschroder et al, 2011;Esquivel et al, 2013).…”

“…volcanii is also the first motile organism to be reported where the initial adhesion to a surface does not require flagella (Tripepi et al, 2010) and where a subset of six identified adhesion pilins (PilA1-A6) are required for microcolony formation, while others appear to inhibit this early step in biofilm formation . Finally, each of these pilins, even though they are rather diverse, has a completely conserved H-domain that is required for the assembly of a pilus (Szabó et al, 2007;Esquivel et al, 2013).…”