The formation and function of plant metabolons

Abstract

SUMMARY Metabolons are temporary structural‐functional complexes of sequential enzymes of a metabolic pathway that are distinct from stable multi‐enzyme complexes. Here we provide a brief history of the study of enzyme–enzyme assemblies with a particular focus on those that mediate substrate channeling in plants. Large numbers of protein complexes have been proposed for both primary and secondary metabolic pathways in plants. However, to date only four substrate channels have been demonstrated. We provide an overview of current knowledge concerning these four metabolons and explain the methodologies that are currently being applied to unravel their functions. Although the assembly of metabolons has been documented to arise through diverse mechanisms, the physical interaction within the characterized plant metabolons all appear to be driven by interaction with structural elements of the cell. We therefore pose the question as to what methodologies could be brought to bear to enhance our knowledge of plant metabolons that assemble via different mechanisms? In addressing this question, we review recent findings in non‐plant systems concerning liquid droplet phase separation and enzyme chemotaxis and propose strategies via which such metabolons could be identified in plants. We additionally discuss the possibilities that could be opened up by novel approaches based on: (i) subcellular‐level mass spectral imaging, (ii) proteomics, and (iii) emergent methods in structural and computational biology.

The Role of TCA Cycle Enzymes in Plants

“…[86] However, this finding remains controversial with many researchers arguing that it remains to be demonstrated in vivo. [37,88]…”

“…Whilst they had been postulated to be involved in structural aspects of the metabolon (dis)assembly, results of a recent study in Bacillus subtilis [36] revealed that some of these interactions occur as a means of inhibiting enzyme function. Given that this is also true of the plant flavonoid pathway and in plant cysteine synthetase, [37] this mechanism may be prevalent in nature. [38] In addition to an understanding of the regulation of the TCA cycle through which metabolites are synthesized, in plants, it is also interesting to consider the interaction between the TCA cycle and photosynthesis, photorespiration, and nitrate assimilation.…”

“…Whilst they had been postulated to be involved in structural aspects of the metabolon (dis)assembly, results of a recent study in Bacillus subtilis [ 36 ] revealed that some of these interactions occur as a means of inhibiting enzyme function. Given that this is also true of the plant flavonoid pathway and in plant cysteine synthetase, [ 37 ] this mechanism may be prevalent in nature. [ 38 ]…”

Editorial – Regulation of Metabolism Special Issue

“…As described by Dahmani et al. (2023), only four such metabolons have been unambiguously defined in plants. This is due to the difficulty in obtaining supporting evidence.…”

“…Over this time particular focus has been placed on enzyme assemblies known as metabolons which perform substrate channelling. As described by Dahmani et al (2023), only four such metabolons have been unambiguously defined in plants. This is due to the difficulty in obtaining supporting evidence.…”