Backbone NMR resonance assignment of the intrinsically disordered UBact protein from Nitrospira nitrosa.

Ubiquitin signaling in eukaryotes is responsible for a variety of cellular outcomes, most notably proteasomal degradation. A recent bioinformatic study has revealed the existence of a new proteasomal operon in certain gram-negative bacteria phyla. This operon contains genes similar to those included in the prokaryotic ubiquitin-like protein (Pup) proteasomal operon, but do not themselves contain Pup. Instead, they encode for a protein termed UBact with 30% sequence similarity to Pup. Here, we report the near-complete NMR assignment of the backbone and partial assignment of the side chain chemical shifts of the UBact protein from Nitrospira nitrosa. The H-N HSQC spectrum shows a narrow spread of proton NMR signals, characteristic of an intrinsically disordered protein. This chemical shift assignment will facilitate further NMR studies to explore the role of UBact in this new putative proteasomal operon.