A possible disk to cylinder transition of assemblies of feast/famine regulatory proteins, FFRPs

We have crystallized the protein pot0434017 from the archaeon Pyrococcus sp. OT3. In the crystals dimers of this protein are arranged into helical cylinders, continuing through the crystals by crossing over asymmetric units; 6 sets of dimers forming each helical turn. While, formation of disks in crystals by 4 sets of dimers was reported for similar proteins (pot1216151 from P. OT3 and LrpA from Pyrococcus furiosus). These archaeal proteins and E. coli transcription factors, Lrp (leucine-responsible regulatory protein) and AsnC (aspargine synthesis C gene product), together with a large number of other archaeal and eubacterial proteins, form a large protein family; for which the classification feast/famine regulatory proteins (FFRPs) is proposed. On the basis of an analysis of the assembly forms of FFRPs, and on the basis of identification of numbers and types of ffrp genes coded in various bacterial genomes, possible biological roles of FFRPs are discussed.