Wing phosphorylation is a major functional determinant of the Lrs14‐type biofilm and motility regulator AbfR1 in Sulfolobus acidocaldarius

Abstract

Summary In response to a variety of environmental cues, prokaryotes can switch between a motile and a sessile, biofilm‐forming mode of growth. The regulatory mechanisms and signaling pathways underlying this switch are largely unknown in archaea but involve small winged helix‐turn‐helix DNA‐binding proteins of the archaea‐specific Lrs14 family. Here, we study the Lrs14 member AbfR1 of Sulfolobus acidocaldarius. Small‐angle X‐ray scattering data are presented, which are consistent with a model of dimeric AbfR1 in which dimerization occurs via an antiparallel coiled coil as suggested by homology modeling. Furthermore, solution structure data of AbfR1‐DNA complexes suggest that upon binding DNA, AbfR1 induces deformations in the DNA. The wing residues tyrosine 84 and serine 87, which are phosphorylated in vivo, are crucial to establish stable protein‐DNA contacts and their substitution with a negatively charged glutamate or aspartate residue inhibits formation of a nucleoprotein complex. Furthermore, mutation abrogates the cellular abundance and transcription regulatory function of AbfR1 and thus affects the resulting biofilm and motility phenotype of S. acidocaldarius. This work establishes a novel wHTH DNA‐binding mode for Lrs14‐like proteins and hints at an important role for protein phosphorylation as a signal transduction mechanism for the control of biofilm formation and motility in archaea.

Peer Review #2 of "Two membrane-bound transcription factors regulate expression of various type-IV-pili surface structures in Sulfolobus acidocaldarius (v0.1)"

“…Reversible protein phosphorylation is known to regulate the activity of archaellum regulators (Hoffmann et al, 2016;Haurat et al, 2017;Li et al, 2017). Therefore,it is tempting to speculate that ArnR and ArnR1 are also regulated by phosphorylation.…”

“…The archaellum of S. acidocaldarius consists of seven proteins (FlaB, FlaX, FlaG, FlaF, FlaH, FlaI, and FlaJ) that are encoded in an operon whose transcription is controlled by two promoters (pflaB and pflaX) (Lassak et al, 2012). Expression of the archaellum is tightly regulated by a complex network of positive and negative regulators and phosphorylation by various protein kinases plays a fundamental role in the regulatory process (Hoffmann et al, 2016;Haurat et al, 2017;Li et al, 2017). Especially the promoter upstream of the gene encoding the archaellum filament protein FlaB is strongly induced upon PeerJ reviewing PDF | (2018:11:32552:1:1:NEW 9 Jan 2019)…”

Crystal structure of an Lrs14-like archaeal biofilm regulator fromSulfolobus acidocaldarius

“…Treatment with reducing agents such as -mercaptoethanol was found to destabilize the Sto12a dimer. Small-angle X-ray scattering of AbfR1 revealed an overall molecular architecture similar to that of Sto12a, with the typical two-domain architecture, domain-like regions corresponding to the wHTH fold (Li et al, 2017), and dimer stabilization via the C-terminal H4 helices. However, unlike Sto12a, reducing agents failed to interfere with the dimerization of AbfR1 (Li et al, 2017).…”

“…A recent study on AbfR1 pointed to phosphorylation-mediated regulation of its function (Li et al, 2017). Phosphoproteomic analysis of S. acidocaldarius shows that Tyr84 and Ser87 of AbfR1 can be phosphorylated; accordingly, mutation of these residues to either alanine and/or respective phosphomimetic residues significantly induces EPS production, similar to the abfR1 deletion phenotype (Li et al, 2017;Reimann et al, 2013).…”

“…The SAXS-based solution structure of the AbfR1 ortholog, when complexed with dsDNA of 40 bp, reflects considerable bending of the straight B-DNA at both ends, resulting in an S-shaped complex. In AbfR1, the phosphorylation-dependent modulation of DNA binding regulates biofilm formation and motility in S. acidocaldarius (Li et al, 2017). Notably, Lrs14like proteins were co-immunoprecipitated together with the nucleoid-associated proteins Sso7d and Alba (Fiorentino et al, 2003).…”