Pathway · 3 proteins
Metal installation
Scaffolds, carriers and chaperones help deliver metals to proteins.
How it works
- Iron-sulfur cluster assembly is represented by a scaffold protein and by ErpA, an insertion protein: the scaffold builds the cluster, and the insertion protein hands it to a recipient.
- HypA is a nickel metallochaperone used in hydrogenase maturation, and a PCu(A)C-family copper chaperone delivers copper to its targets. Both are delivery proteins, not enzymes of their own pathways.
- Delivery is what makes an imported metal useful. The recipients appear in the module below and in system 16, where cluster and metallocofactor assembly is described in more detail.
Grouped by the atlas’s curated pathway map. The table order is not a proven reaction order.
Its proteins
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Copper chaperone PCu(A)C | — | — | — | 151 | System only |
| Protein aq_1857 | — | — | — | 116 | Step named |
| Iron-sulfur cluster assembly scaffold protein IscU | — | — | [2Fe-2S] cluster | 157 | Step named |
Also part of this pathway
These proteins are described under another pathway, but also take part here.
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Hydrogenase maturation factor HypAHome: Not yet placed in a pathway | — | — | Ni(2+), Zn(2+) | 115 | Step named |
Origins
How could iron-sulfur clusters and other metal centres be put into enzymes before assembly proteins existed?
Iron-sulfur minerals feature in metabolism-first proposals, but the books searched describe no prebiotic route by which clusters were loaded into proteins.
Iron-sulfur clusters are built on a scaffold protein from sulfur supplied by cysteine desulfurase, then handed to their target enzymes. In some cells the cluster even switches a protein's job: aconitase without its cluster becomes a regulator that binds messenger RNA to control iron use.
From the books: Nelson & Cox, Lehninger Principles of Biochemistry, p. 624.
The wider question for this part of the cell: origins for loading metals into enzymes.
Sources
- Atlas pathway grouping from the VF5 reference-genome system map (Deckert et al. 1998; Braakman & Smith 2014)
Other pathways in this group: NiFe-hydrogenase maturation · Not yet placed in a pathway