DNA Wrapping by a Tetrameric Bacterial Histone

Abstract

Histones are conserved DNA-packaging proteins found across all domains of life. In eukaryotes, canonical histones form octamers that wrap [~]147 base pairs of DNA into nucleosomes -- the fundamental units of chromatin. In archaea, histones form dimers that further multimerize into extended hypernucleosomes along DNA. Although bacteria were long thought to lack histones, recent studies have uncovered histone homologs in diverse bacterial lineages, many of which possess key DNA-binding features. We previously characterized HBb, a bacterial histone from Bdellovibrio bacteriovorus, which binds DNA as a dimer and induces bending. Here, we describe HLp from Leptospira perolatii, a representative of a distinct bacterial histone group. Crystallographic and biophysical analyses reveal that HLp forms stable tetramers. Like HBb, HLp binds DNA non-specifically; however, it adopts a different mode of interaction -- wrapping [~]60 base pairs of DNA around its tetrameric core. This wrapping mode, supported by molecular dynamics simulations and DNA-binding assays, promotes DNA compaction and alters its topology. When expressed heterologously in Escherichia coli, HLp reorganizes nucleoid morphology, consistent with a role in chromatin organization. These findings expand the known repertoire of histone-DNA interaction in bacteria and underscore the structural and functional diversity of histone-based genome organization across the tree of life.