Solution Structure and Dynamics of the Small Protein HVO_2922 from Haloferax volcanii

Past sequencing campaigns overlooked small proteins as they seemed to be irrelevant due to their small size. However, their occurrence is widespread, and there is growing evidence that these small proteins are in fact functionally very important in organisms found in all kingdoms of life. Within a global proteome analysis for small proteins of the archaeal model organism Haloferax volcanii, the HVO_2922 protein has been identified. It is differentially expressed in response to changes in iron and salt concentrations, thus suggesting that its expression is stress‐regulated. The protein is conserved among Haloarchaea and contains an uncharacterized domain of unknown function (DUF1508, UPF0339 family protein). We elucidated the NMR solution structure, which shows that the isolated protein forms a symmetrical dimer. The dimerization is found to be concentration‐dependent and essential for protein stability and most likely for its functionality, as mutagenesis at the dimer interface leads to a decrease in stability and protein aggregation. It takes two: We present a high‐resolution NMR solution structure of the HVO_2922 small protein from H. volcanii. The isolated protein forms a symmetrical dimer, which is stabilized by intramonomer electrostatic interactions. Dimerization is crucial for the protein stability and most probably for its functionality.