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Heme can be immobilized in different protein scaffolds

The symbiotic relationship between legumes and the bacteria that grows on their roots is essential for plant survival. Without these bacteria, plants would have no source of nitrogen, an element necessary to build proteins and other biomolecules, that depend on nitrogen fertilizers in the soil.

To create this symbiotic relationship, some legumes produce hundreds of peptides that help bacteria live in structures called nodules at their roots. A new MIT study shows that one of these peptides has an unexpected function: It absorbs all available heme, an iron-containing molecule. This puts the bacteria into iron starvation mode, which increases the production of ammonia, a form of nitrogen available to plants.

"This is the first of 700 peptides in this system that has been formulated in great detail," said senior investigator Graham Walker, American Cancer Society Research Professor of Biology at MIT and Howard Hughes Medical Institute professor. Molecular Mechanisms." the study's authors.

Nature utilizes enzymes to perform countless biological functions unmatched by the synthetic counterparts 1 and 2. One of the most impressive examples is heme enzymes, in which heme units are immobilized in different protein scaffolds to perform specific tasks, including substrate oxidation3,4, electron transfer5,6, sensing7, metal Ion storage8, and transport9. For example, cytochrome c (Cyt c), in which heme is covalently bound to the protein scaffold via two disulfide bonds and axially coordinated by histidine (H18) and methionine (M80) Bit, is a highly stable heme protein that acts as a component of the electron transport chain in mitochondria 10 . Whereas in oxidoreductases such as catalase (CAT) and peroxidase, heme was found to be immobilized by weak non-covalent interactions, and their Fe active site was coordinated by only one axial amino acid. bit. The resulting high-spin iron species favors substrate affinity and thus accelerates biocatalysis12. Therefore, these oxidoreductases play a critical role in preventing oxidative damage to cellular components caused by reactive oxygen species and their highly reactive breakdown products13,14 protective effect. We envy nature's ability to program enzyme conformations in highly crowded cellular environments and provide enzymes with on-demand biological activity. Growing efforts have shown that this complex programming relies on a group of conserved proteins called chaperones, for example, the typical GroEL-GroES chaperone in bacteria (Fig. 1a). The GroEL-GroES system is a large bicyclic complex. It has a cage-like structure capable of encapsulating unfolded or non-native proteins and then forms a highly hydrophilic, net negatively charged inner wall to regulate protein folding17. This has inspired scientists to use synthetic nanocages to tune the conformation of enzymes, but it remains a long-standing challenge.

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