Pathway · 3 proteins
Substrate recognition
Binding proteins and transporter components provide substrate-selection functions.
How it works
- Substrate-binding proteins can capture solutes and deliver them to a compatible uptake transporter. PstS, molybdate-binding and Zn/Mn-binding family annotations suggest candidate substrate classes.
- Binding and transfer to the membrane machinery are distinct from ATP hydrolysis by an ABC ATP-binding component. ATPase annotations alone generally do not specify the transported substance.
- A functional uptake system requires the correct binding, permease and energy-coupling partners. This mixed annotation group does not establish one-to-one pairings or exact substrate specificity for every protein.
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 |
|---|---|---|---|---|---|
| ABC transporter (MsbA subfamily) | — | — | — | 554 | Step named |
| Lipoprotein-releasing system ATP-binding protein LolD | 7.6.2.- | — | — | 224 | Step named |
| Lipopolysaccharide export system ATP-binding protein LptB | — | — | — | 238 | 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 |
|---|---|---|---|---|---|
| ABC transporter substrate-binding proteinHome: Not yet placed in a pathway | — | — | — | 319 | System only |
| Phosphate import ATP-binding protein PstBHome: ATP-coupled transport | 7.3.2.1 | phosphate(out) + ATP + H2O = ADP + 2 phosphate(in) + H(+) | — | 257 | Step named |
| ABC transporterHome: ATP-coupled transport | — | — | Mg(2+) | 396 | Step named |
| ABC transporterHome: ATP-coupled transport | — | — | — | 247 | Step named |
| Phosphate-binding proteinHome: Substrate recognition | — | — | — | 337 | Step named |
| ABC transporterHome: ATP-coupled transport | — | — | — | 305 | Step named |
| ABC transporterHome: ATP-coupled transport | — | — | — | 251 | Step named |
| Adhesion proteinHome: Ion exchange | — | — | — | 290 | System only |
| Adhesion BHome: Ion exchange | — | — | — | 278 | Step named |
| ABC transporterHome: ATP-coupled transport | — | — | — | 232 | Step named |
Origins
How could a cell take up the nutrients it needs, and only those, before binding proteins existed?
None of the books searched discusses the origin of substrate-binding proteins.
Each ABC transporter is thought to be specific for a particular molecule or class of molecules. Its binding protein catches the right one outside the membrane and hands it to the transporter, which spends ATP to move it in. Without that selectivity, a membrane either keeps everything out or lets everything through.
From the books: Alberts et al., Molecular Biology of the Cell, p. 650.
The wider question for this part of the cell: origins for building and maintaining the membrane.
Sources
- Atlas pathway grouping from the VF5 reference-genome system map (Deckert et al. 1998; Braakman & Smith 2014)
Other pathways in this group: Glycerolipid assembly · Lipid A and outer envelope · Fatty-acid elongation · Terpenoid backbone biosynthesis · Fatty acid biosynthesis · Lipopolysaccharide biosynthesis · Biosynthesis of various nucleotide sugars · Not yet placed in a pathway