PMCID
stringclasses 30
values | Title
stringclasses 30
values | Sentences
stringlengths 2
1.94k
|
|---|---|---|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In plants, transporter phosphorylation and dephosphorylation are known to regulate activity29.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In S. cerevisiae, phosphorylation of Ser457 within the C-terminal region (CTR) in the cytoplasm was recently proposed to cause Mep2 opening, possibly via inducing a conformational change30.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
To elucidate the mechanism of Mep2 transport regulation, we present here X-ray crystal structures of the Mep2 transceptors from S. cerevisiae and C. albicans.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The structures are similar to each other but show considerable differences to all other ammonium transporter structures.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The most striking difference is the fact that the Mep2 proteins have closed conformations.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The putative phosphorylation site is solvent accessible and located in a negatively charged pocket ∼30 Å away from the channel exit.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The channels of phosphorylation-mimicking mutants of C. albicans Mep2 are still closed but show large conformational changes within a conserved part of the CTR.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Together with a structure of a C-terminal Mep2 variant lacking the segment containing the phosphorylation site, the results allow us to propose a structural model for phosphorylation-based regulation of eukaryotic ammonium transport.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The Mep2 protein of S. cerevisiae (ScMep2) was overexpressed in S. cerevisiae in high yields, enabling structure determination by X-ray crystallography using data to 3.2 Å resolution by molecular replacement (MR) with the archaebacterial Amt-1 structure (see Methods section).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Given that the modest resolution of the structure and the limited detergent stability of ScMep2 would likely complicate structure–function studies, several other fungal Mep2 orthologues were subsequently overexpressed and screened for diffraction-quality crystals.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Of these, Mep2 from C. albicans (CaMep2) showed superior stability in relatively harsh detergents such as nonyl-glucoside, allowing structure determination in two different crystal forms to high resolution (up to 1.5 Å).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Despite different crystal packing (Supplementary Table 1), the two CaMep2 structures are identical to each other and very similar to ScMep2 (Cα r.m.s.d. (
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
root mean square deviation)=0.7 Å for 434 residues), with the main differences confined to the N terminus and the CTR (Fig. 1).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Electron density is visible for the entire polypeptide chains, with the exception of the C-terminal 43 (ScMep2) and 25 residues (CaMep2), which are poorly conserved and presumably disordered.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Both Mep2 proteins show the archetypal trimeric assemblies in which each monomer consists of 11 TM helices surrounding a central pore.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Important functional features such as the extracellular ammonium binding site, the Phe gate and the twin-His motif within the hydrophobic channel are all very similar to those present in the bacterial transporters and RhCG1213141516171819.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In the remainder of the manuscript, we will specifically discuss CaMep2 due to the superior resolution of the structure.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Unless specifically stated, the drawn conclusions also apply to ScMep2.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
While the overall architecture of Mep2 is similar to that of the prokaryotic transporters (Cα r.m.s.d.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
with Amt-1=1.4 Å for 361 residues), there are large differences within the N terminus, intracellular loops (ICLs) ICL1 and ICL3, and the CTR.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The N termini of the Mep2 proteins are ∼20–25 residues longer compared with their bacterial counterparts (Figs 1 and 2), substantially increasing the size of the extracellular domain.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Moreover, the N terminus of one monomer interacts with the extended extracellular loop ECL5 of a neighbouring monomer.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Together with additional, smaller differences in other extracellular loops, these changes generate a distinct vestibule leading to the ammonium binding site that is much more pronounced than in the bacterial proteins.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The N-terminal vestibule and the resulting inter-monomer interactions likely increase the stability of the Mep2 trimer, in support of data for plant AMT proteins31.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
However, given that an N-terminal deletion mutant (2-27Δ) grows as well as wild-type (WT) Mep2 on minimal ammonium medium (Fig. 3 and Supplementary Fig. 1), the importance of the N terminus for Mep2 activity is not clear.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The largest differences between the Mep2 structures and the other known ammonium transporter structures are located on the intracellular side of the membrane.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In the vicinity of the Mep2 channel exit, the cytoplasmic end of TM2 has unwound, generating a longer ICL1 even though there are no insertions in this region compared to the bacterial proteins (Figs 2 and 4).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
ICL1 has also moved inwards relative to its position in the bacterial Amts.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The largest backbone movements of equivalent residues within ICL1 are ∼10 Å, markedly affecting the conserved basic RxK motif (Fig. 4).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The head group of Arg54 has moved ∼11 Å relative to that in Amt-1, whereas the shift of the head group of the variable Lys55 residue is almost 20 Å. The side chain of Lys56 in the basic motif points in an opposite direction in the Mep2 structures compared with that of, for example, Amt-1 (Fig. 4).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In addition to changing the RxK motif, the movement of ICL1 has another, crucial functional consequence.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
At the C-terminal end of TM1, the side-chain hydroxyl group of the relatively conserved Tyr49 (Tyr53 in ScMep2) makes a strong hydrogen bond with the ɛ2 nitrogen atom of the absolutely conserved His342 of the twin-His motif (His348 in ScMep2), closing the channel (Figs 4 and 5).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In bacterial Amt proteins, this Tyr side chain is rotated ∼4 Å away as a result of the different conformation of TM1, leaving the channel open and the histidine available for its putative role in substrate transport (Supplementary Fig. 2)16.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Compared with ICL1, the backbone conformational changes observed for the neighbouring ICL2 are smaller, but large shifts are nevertheless observed for the conserved residues Glu140 and Arg141 (Fig. 4).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Finally, the important ICL3 linking the pseudo-symmetrical halves (TM1-5 and TM6-10) of the transporter is also shifted up to ∼10 Å and forms an additional barrier that closes the channel on the cytoplasmic side (Fig. 5).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
This two-tier channel block likely ensures that very little ammonium transport will take place under nitrogen-sufficient conditions.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The closed state of the channel might also explain why no density, which could correspond to ammonium (or water), is observed in the hydrophobic part of the Mep2 channel close to the twin-His motif.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Significantly, this is also true for ScMep2, which was crystallized in the presence of 0.2 M ammonium ions (see Methods section).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The final region in Mep2 that shows large differences compared with the bacterial transporters is the CTR.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In Mep2, the CTR has moved away and makes relatively few contacts with the main body of the transporter, generating a more elongated protein (Figs 1 and 4).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
By contrast, in the structures of bacterial proteins, the CTR is docked tightly onto the N-terminal half of the transporters (corresponding to TM1-5), resulting in a more compact structure.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
This is illustrated by the positions of the five universally conserved residues within the CTR, that is, Arg415(370), Glu421(376), Gly424(379), Asp426(381) and Tyr 435(390) in CaMep2(Amt-1) (Fig. 2).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
These residues include those of the ‘ExxGxD' motif, which when mutated generate inactive transporters3233.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In Amt-1 and other bacterial ammonium transporters, these CTR residues interact with residues within the N-terminal half of the protein.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
On one side, the Tyr390 hydroxyl in Amt-1 is hydrogen bonded with the side chain of the conserved His185 at the C-terminal end of loop ICL3.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
At the other end of ICL3, the backbone carbonyl groups of Gly172 and Lys173 are hydrogen bonded to the side chain of Arg370.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Similar interactions were also modelled in the active, non-phosphorylated plant AtAmt-1;1 structure (for example, Y467-H239 and D458-K71)33.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The result of these interactions is that the CTR ‘hugs' the N-terminal half of the transporters (Fig. 4).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Also noteworthy is Asp381, the side chain of which interacts strongly with the positive dipole on the N-terminal end of TM2.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
This interaction in the centre of the protein may be particularly important to stabilize the open conformations of ammonium transporters.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In the Mep2 structures, none of the interactions mentioned above are present.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Recently Boeckstaens et al. provided evidence that Ser457 in ScMep2 (corresponding to Ser453 in CaMep2) is phosphorylated by the TORC1 effector kinase Npr1 under nitrogen-limiting conditions30.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In the absence of Npr1, plasmid-encoded WT Mep2 in a S. cerevisiae mep1-3Δ strain (triple mepΔ) does not allow growth on low concentrations of ammonium, suggesting that the transporter is inactive (Fig. 3 and Supplementary Fig. 1)30.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Conversely, the phosphorylation-mimicking S457D variant is active both in the triple mepΔ background and in a triple mepΔ npr1Δ strain (Fig. 3)30.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Mutation of other potential phosphorylation sites in the CTR did not support growth in the npr1Δ background30.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Collectively, these data suggest that phosphorylation of Ser457 opens the Mep2 channel to allow ammonium uptake.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Ser457 is located in a part of the CTR that is conserved in a subgroup of Mep2 proteins, but which is not present in bacterial proteins (Fig. 2).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
This segment (residues 450–457 in ScMep2 and 446–453 in CaMep2) was dubbed an autoinhibitory (AI) region based on the fact that its removal generates an active transporter in the absence of Npr1 (Fig. 3)30.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Where is the AI region and the Npr1 phosphorylation site located?
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Our structures reveal that surprisingly, the AI region is folded back onto the CTR and is not located near the centre of the trimer as expected from the bacterial structures (Fig. 4).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The AI region packs against the cytoplasmic ends of TM2 and TM4, physically linking the main body of the transporter with the CTR via main chain interactions and side-chain interactions of Val447, Asp449, Pro450 and Arg452 (Fig. 6).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The AI regions have very similar conformations in CaMep2 and ScMep2, despite considerable differences in the rest of the CTR (Fig. 6).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Strikingly, the Npr1 target serine residue is located at the periphery of the trimer, far away (∼30 Å) from any channel exit (Fig. 6).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Despite its location at the periphery of the trimer, the electron density for the serine is well defined in both Mep2 structures and corresponds to the non-phosphorylated state (Fig. 6).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
This makes sense since the proteins were expressed in rich medium and confirms the recent suggestion by Boeckstaens et al. that the non-phosphorylated form of Mep2 corresponds to the inactive state30.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
For ScMep2, Ser457 is the most C-terminal residue for which electron density is visible, indicating that the region beyond Ser457 is disordered.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In CaMep2, the visible part of the sequence extends for two residues beyond Ser453 (Fig. 6).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The peripheral location and disorder of the CTR beyond the kinase target site should facilitate the phosphorylation by Npr1.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The disordered part of the CTR is not conserved in ammonium transporters (Fig. 2), suggesting that it is not important for transport.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Interestingly, a ScMep2 457Δ truncation mutant in which a His-tag directly follows Ser457 is highly expressed but has low activity (Fig. 3 and Supplementary Fig. 1b), suggesting that the His-tag interferes with phosphorylation by Npr1.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The same mutant lacking the His-tag has WT properties (Supplementary Fig. 1b), confirming that the region following the phosphorylation site is dispensable for function.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Given that Ser457/453 is far from any channel exit (Fig. 6), the crucial question is how phosphorylation opens the Mep2 channel to generate an active transporter.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Boeckstaens et al. proposed that phosphorylation does not affect channel activity directly, but instead relieves inhibition by the AI region.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The data behind this hypothesis is the observation that a ScMep2 449-485Δ deletion mutant lacking the AI region is highly active in MA uptake both in the triple mepΔ and triple mepΔ npr1Δ backgrounds, implying that this Mep2 variant has a constitutively open channel30.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
We obtained a similar result for ammonium uptake by the 446Δ mutant (Fig. 3), supporting the data from Marini et al. We then constructed and purified the analogous CaMep2 442Δ truncation mutant and determined the crystal structure using data to 3.4 Å resolution.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The structure shows that removal of the AI region markedly increases the dynamics of the cytoplasmic parts of the transporter.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
This is not unexpected given the fact that the AI region bridges the CTR and the main body of Mep2 (Fig. 6).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Density for ICL3 and the CTR beyond residue Arg415 is missing in the 442Δ mutant, and the density for the other ICLs including ICL1 is generally poor with visible parts of the structure having high B-factors (Fig. 7).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Interestingly, however, the Tyr49-His342 hydrogen bond that closes the channel in the WT protein is still present (Fig. 7 and Supplementary Fig. 2).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Why then does this mutant appear to be constitutively active?
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
We propose two possibilities.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The first one is that the open state is disfavoured by crystallization because of lower stability or due to crystal packing constraints.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The second possibility is that the Tyr–His hydrogen bond has to be disrupted by the incoming substrate to open the channel.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The latter model would fit well with the NH3/H symport model in which the proton is relayed by the twin-His motif14.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The importance of the Tyr–His hydrogen bond is underscored by the fact that its removal in the ScMep2 Y53A mutant results in a constitutively active transporter (Fig. 3).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Do the Mep2 structures provide any clues regarding the potential effect of phosphorylation?
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The side-chain hydroxyl of Ser457/453 is located in a well-defined electronegative pocket that is solvent accessible (Fig. 6).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The closest atoms to the serine hydroxyl group are the backbone carbonyl atoms of Asp419, Glu420 and Glu421, which are 3–4 Å away.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
We therefore predict that phosphorylation of Ser453 will result in steric clashes as well as electrostatic repulsion, which in turn might cause substantial conformational changes within the CTR.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
To test this hypothesis, we determined the structure of the phosphorylation-mimicking R452D/S453D protein (hereafter termed ‘DD mutant'), using data to a resolution of 2.4 Å. The additional mutation of the arginine preceding the phosphorylation site was introduced (i) to increase the negative charge density and make it more comparable to a phosphate at neutral pH, and (ii) to further destabilize the interactions of the AI region with the main body of the transporter (Fig. 6).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
The ammonium uptake activity of the S. cerevisiae version of the DD mutant is the same as that of WT Mep2 and the S453D mutant, indicating that the mutations do not affect transporter functionality in the triple mepΔ background (Fig. 3).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Unexpectedly, the AI segment containing the mutated residues has only undergone a slight shift compared with the WT protein (Fig. 8 and Supplementary Fig. 3).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
By contrast, the conserved part of the CTR has undergone a large conformational change involving formation of a 12-residue-long α-helix from Leu427 to Asp438.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In addition, residues Glu420-Leu423 including Glu421 of the ExxGxD motif are now disordered (Fig. 8 and Supplementary Fig. 3).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
Overall, ∼20 residues are affected by the introduced mutations.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
This is the first time a large conformational change has been observed in an ammonium transporter as a result of a mutation, and confirms previous hypotheses that phosphorylation causes structural changes in the CTR293033.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
To exclude the possibility that the additional R452D mutation is responsible for the observed changes, we also determined the structure of the ‘single D' S453D mutant.
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
As shown in Supplementary Fig. 4, the consequence of the single D mutation is very similar to that of the DD substitution, with conformational changes and increased dynamics confined to the conserved part of the CTR (Supplementary Fig. 4).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
To supplement the crystal structures, we also performed modelling and MD studies of WT CaMep2, the DD mutant and phosphorylated protein (S453J).
|
PMC4852598
|
Structural basis for Mep2 ammonium transceptor activation by phosphorylation.
|
In the WT structure, the acidic residues Asp419, Glu420 and Glu421 are within hydrogen bonding distance of Ser453.
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.