One member of a gro-ESL-like chaperonin multigene family in Bradyrhizobium japonicum is co-regulated with symbiotic nitrogen fixation genes.

Abstract

This report is concerned with the structural characterization and genetic regulation of new bacterial groES and groEL chaperonin genes, and presents two novelties. The first is the discovery that the nitrogen fixing soybean root nodule bacterium, Bradyrhizobium japonicum, unlike all other prokaryotes investigated so far, possesses a multigene family consisting of five very similar, though not identical, groESL‐like genes. The second novelty relates to the finding that these five homologues are expressed to different degrees and, in particular, that one family member (namely groESL3) is induced by a mechanism that does not involve the well‐known heat shock response. By contrast, the groESL3 genes are co‐regulated together with symbiotic nitrogen fixation genes, in that they are activated by the nitrogen fixation regulatory protein NifA at low oxygen conditions and transcribed from a −24/−12 promoter by the sigma 54 RNA polymerase. Two other members of the groESL gene family are apparently expressed constitutively at different levels, and yet another one is strongly induced by high temperature. As an attractive hypothesis it follows that B. japonicum may modulate its cellular contents of GroES‐ and GroEL‐like chaperonins in response to specific environmental conditions and physiological needs.

Multiple chaperonins in bacteria—novel functions and non-canonical behaviors

“…Upon heat shock, HrcA is destabilized, released from the CIRCE element, allowing the production of heat-shock proteins, which in turn attend to the cellular stressed proteins till normalcy is resumed. Upon recommencement of normalcy, GroEL, free from cellular stressed proteins, facilitates the folding and assembly of HrcA and the repression of the downstream genes of groEL genes (Kong et al 1993;Fischer et al 1993;Karunakaran et al 2003;Barreiro et al 2005). The existence of multiple groEL genes opens up several hypotheses on their function and evolution and on the distribution of the substrates.…”

“…These bacteria offer an interesting picture for multiple chaperonin genes (Rusanganwa and Gupta 1993;Wallington and Lund 1994), boasting the highest number of chaperonin genes among bacteria. Bradyrhizobium japonicum hosts seven groEL genes with five of them in operonic arrangement with groES homologues (Fischer et al 1993;Kaneko et al 2000Kaneko et al , 2002, and at least one of the multiple GroELs has been dedicated for folding proteins involved in nitrogen fixation. Interestingly, several non-rhizobial nitrogen-fixing bacteria bear three to four copies of chaperonin genes (Moulin et al 2001;Normand et al 2007), while non-nitrogen-fixing rhizobia have only one copy (Wood et al 2001), suggesting a correlation between the presence of multiple chaperonins and nitrogen fixation pathway.…”

Multiple Gene Duplication and Rapid Evolution in the groEL Gene: Functional Implications

“…Different copies of groELs might have diverged sequentially in a later event to attain the ability to function under different conditions of stress. Indeed it has been reported that in B. japonicum expression of the groEL5 gene is regulated by cellular oxygen and that of groEL3 is regulated by the nitrogen fixation system (Fischer et al 1993). However, inferences regarding the chain of evolutionary events within the rhizobial clade cannot be drawn due to weak statistical support.…”

The chaperone GroEL is required for the final assembly of the molybdenum-iron protein of nitrogenase

“…Unfortunately, commercially available E. coli GroES antibodies showed extensive nonspecific crossreactivity with these solutions and were therefore not helpful in this regard. Since the early 1990s, when GroEL research was in its infancy, several reports have appeared suggesting that GroEL might have something to do with nitrogenase regulation and assembly (40)(41)(42)(43)(44). For example, 35 S pulse-chase experiments with Klebsiella pneumoniae suggested transient binding of newly synthesized Fe protein and MoFe protein polypeptides to GroEL.…”