EMBO/soda-nel huggingface dataset:
Coupling of mitochondrial function and skeletal muscle fiber type by a miR-499/Fnip1/AMPK circuit (2016)
Figure 2

Figure 2. MCK-miR-499 muscle is reprogrammed for increased capacity for mitochondrial oxidation.

(A) Gene ontology (GO) enrichment analysis of gene transcripts up-regulated in MCK-miR-499 muscle identified a number of terms related to mitochondrial function and muscle contraction. Gene expression array data generated from the gastrocnemius muscle of 8-week-old male MCK-miR-499 mice were compared to littermate controls (NTG).

(B) Expression of the nuclear-encoded and mitochondrial-encoded genes (RT-qPCR) in the gastrocnemius muscle from the indicated genotypes (n = 5 mice per group). *p < 0.05.

(C) Representative western blot analysis performed with gastrocnemius muscle total protein extracts prepared from the indicated mice using myoglobin, cytochrome c, and β-actin (control) antibodies (n = 8 mice per group).

(D) Expression of genes (RT-qPCR) involved in muscle glucose and fatty acids metabolism in the gastrocnemius muscle from the indicated genotypes (n = 5 mice per group). *p < 0.05.

(E) LDH isoenzymes were separated by polyacrylamide gel electrophoresis using whole cell extracts from NTG heart (Ht, control) and gastrocnemius muscle from the indicated mice. A representative gel showing 3-4 independent mice per group is shown.

(F) Quantification of LDH isoenzyme activity gel electrophoresis in E. Values represent the mean % (+/- SEM) total LDH activity. *p < 0.05.

(G) Cross-section of the gastrocnemius muscle from a 3-month-old male NTG and MCK-miR-499 stained for myosin I ATPase activity (Top), SDH (Middle), and α-GPDH (Bottom). Representative images were shown. Scale bar: 500 μm.

All values represent the mean ± SEM. p-value was determined using two-tailed unpaired Student’s t-test.
Coupling of mitochondrial function and skeletal muscle fiber type by a miR-499/Fnip1/AMPK circuit (2016)
Figure 3

Figure 3. miR-499 regulates muscle mitochondrial oxidative capacity through PGC-1α.

(A) (Left) Representative western blot analysis of PGC-1α protein expression in the gastrocnemius muscle from the indicated genotypes, heart (Ht) lysate from WT mice and PGC-1α mKO (MCK-Cre) mice as positive and negative controls, respectively. (Right) Quantification of the PGC-1α/Tubulin signal ratios normalized (=1.0) to the NTG control (n = 5 mice per group). *p = 0.00017.

(B) Expression of the Ldhb, Ldha, Mb (myoglobin), and Cox5a genes (RT-qPCR) in the gastrocnemius muscle from the indicated genotypes (n = 5 mice per group). *p < 0.001 (vs. NTG), ‡p < 0.01 (vs. 499Tg).

(C) (Left) Representative western blot analysis performed with gastrocnemius muscle total protein extracts prepared from the indicated mice using cytochrome c, myoglobin, and α-tubulin (control) antibodies. (Right) Quantification of the Cyt c/Tubulin signal ratios normalized (=1.0) to the NTG control. NTG, n = 5; 499Tg, n = 6; PGC-1α mKO, n = 5; 499Tg/PGC-1α mKO, n = 5. *p < 0.01 (vs. NTG), ‡p = 0.00018 (vs. 499Tg).

(D) Cross-section of gastrocnemius muscle from the indicated mice stained for SDH activity (Top) as well as MHC1 immunofluorescence (IF) (Bottom), Representative images were shown. Scale bar: 500 μm.

(E) Respiratory exchange ratio (RER) during a graded exercise regimen as described in Materials and Methods. Notably, no significant increase in exhaust speed was observed in 499Tg/PGC-1α mKO mice compared to PGC-1α mKO mice. PGC-1α mKO, n = 5; 499Tg/PGC-1α mKO, n = 8.

(F) The bars represent the mean blood lactate levels from the indicated mice following a 25 min run on a motorized treadmill. NTG, n = 9; 499Tg, n = 7; PGC-1α mKO, n = 6; 499Tg/PGC-1α mKO, n = 9. *p = 0.0009 (NTG vs. 499Tg), p = 0.316 (NS, not significant).

All values represent the mean ± SEM. p-value in A and F was determined using two-tailed unpaired Student’s t-test; p-value in B and C was determined using one-way ANOVA coupled to a Fisher’s least-significant difference (LSD) post-hoc test.
Coupling of mitochondrial function and skeletal muscle fiber type by a miR-499/Fnip1/AMPK circuit (2016)
Figure 4

Figure 4. miR-499 directly targets Fnip1.

(A) The schematic shows the putative conserved miR-499 binding site within the 3’ UTR of the Fnip1 gene.

(B) Luciferase reporters containing the wild-type Fnip1 3’UTR or Fnip1 3’UTR mutated in the predicted binding site of miR-499 were used in cotransfection studies in HEK293T cells in the presence or absence of plasmid expressing miR-499 (n = 3 independent experiments). *p < 0.0001 (Fnip1 3’UTR); *p = 0.023 (Mutated).

(C) RT-qPCR analysis of Fnip1 and Fnip2 mRNA levels in the gastrocnemius muscle of the indicated genotypes (n = 5 mice per group).

(D) (Top) Fnip1 protein expression in the gastrocnemius muscle from the indicated mice. (Bottom) Quantification of the Fnip1/Tubulin signal ratio (n = 4 mice per group). *p = 0.014.

All values represent the mean ± SEM. p-value was determined using two-tailed unpaired Student’s t-test.
Coupling of mitochondrial function and skeletal muscle fiber type by a miR-499/Fnip1/AMPK circuit (2016)
Figure 5

Figure 5. Inhibition of Fnip1 reactivated AMPK-PGC-1α signaling and mitochondrial function in myocytes.

(A) (Left) Representative western blot analysis performed on extracts of myotubes subjected to Fnip1 siRNA or control (Con) siRNA using phospho-AMPKα (Thr172) and AMPKα antibodies. (Right) Quantification of the p-AMPKα/AMPKα signal ratios (n = 3 independent experiments). *p = 0.037.

(B, C) Results of RT-qPCR analysis for WT primary mouse myotubes after transfection with Fnip1 siRNAs or scrambled Con siRNAs as indicated. For C, 48 h post-siRNA transfection, myotubes were treated for 24 h with DMSO or 10 μm compound C before harvest (n = 3 independent experiments). *p < 0.0001 (Fnip1 in B), *p = 0.0001 (PGC-1α in B); *p < 0.0001 (vs. Con siRNA in C), ‡p < 0.0001 (vs. Fnip1 siRNA in C ).

(D) (Top) Representative western blot analysis performed on extracts of the gastrocnemius muscle isolated from NTG or MCK-miR-499 mice using phospho-AMPKα (Thr172), AMPKα, phospho-ACC (Ser79), or total ACC antibodies. (Bottom) Quantification of the p-AMPKα/AMPKα and p-ACC/ACC signal ratios normalized (=1.0) to the NTG control (n = 8 mice per group). *p < 0.01.

(E) Oxygen consumption rates (OCR) in primary mouse myotubes transfected with Fnip1 siRNA or Con siRNA. n = 7 separate experiments done with 5 biological replicates. *p < 0.05 (Pyruvate), *p < 0.01 (FCCP).

(F) Results of RT-qPCR analysis for WT primary mouse myotubes subjected to inhibition of both miR-499 and miR-208b (Anti-miRs) (n = 4 independent experiments). *p = 0.037 (Ppargc1a), *p = 0.0019 (Fnip1).

(G) Oxygen consumption rates (OCR) in primary mouse myotubes transfected with miR-499/miR-208b inhibitors alone and together with the presence of Fnip1 siRNA. n = 4 separate experiments done with 5 biological replicates. *p < 0.01 (Anti-miRs vs. Control).

All values represent the mean ± SEM. p-value in A, B, D, E, and F was determined using two-tailed unpaired Student’s t-test; p-value in C and G was determined using one-way ANOVA coupled to a Fisher’s least-significant difference (LSD) post-hoc test.
Coupling of mitochondrial function and skeletal muscle fiber type by a miR-499/Fnip1/AMPK circuit (2016)
Figure 6

Figure 6. Restoring the expression of miR-499 activates the slow-oxidative muscle fiber program and ameliorates muscular dystrophy in mdx mice.

(A) Mean expression levels (RT-qPCR) in gastrocnemius muscle of 8-week-old male WT and mdx mice (n = 5 mice per group). *p = 0.009 (Myh7b), *p = 0.0007 (miR-499), *p = 0.0143 (Myh7), *p < 0.0011 (miR-208b).

(B) Mitochondrial respiration rates were determined from mitochondria isolated from the hindlimb muscle of the indicated mice using pyruvate as substrate. n = 3 separate experiments done with 7-8 biological replicates. *p < 0.01 (ADP).

(C) (Left) Representative western blot analysis of PGC-1α (Top) and Fnip1 (Bottom) protein expression in the gastrocnemius muscle from the indicated genotypes with α-tubulin as the loading control. (Right) Quantification of thePGC-1α/Tubulin and Fnip1/Tubulin signal ratios normalized (=1.0) to the WT control. WT, n = 8; mdx, n = 5; mdx/499Tg, n = 7. *p < 0.0001 (vs. WT), ‡p < 0.0001 (vs. mdx).

(D) Representative western blot analysis of myoglobin protein expression in the gastrocnemius muscle from the indicated genotypes with α-tubulin as the loading control (n = 5 mice per group).

(E) (Top) Representative MHC1 immunofluorescence (IF) in the soleus of the indicated genotypes. Scale bar: 500 μm. (Bottom) Representative H&E staining of the gastrocnemius muscle of the indicated genotypes. Scale bar: 100 μm.

(F) 5-week-old male WT, mdx, and mdx/MCK-miR-499 mice were euthanized and serum creatine kinase activity was determined. WT, n = 10; mdx, n = 10; mdx/499Tg, n = 14. *p < 0.0001 (vs. WT), ‡p = 0.0003 (vs. mdx).

(G) The bars represent the mean running time and distance (± SEM) for 8-week-old male mice on a motorized treadmill. WT, n = 10; mdx, n = 13; mdx/499Tg, n = 8. *p = 0.01406 (Running time, vs. WT), ‡p = 0.005756 (Running time, vs. mdx). *p = 0.004558 (Running distance, vs. WT), ‡p = 0.001668 (Running distance, vs. mdx).

(H) Respiratory exchange ratio (RER) during a graded exercise regimen on a motorized treadmill. mdx, n = 8; mdx/499Tg, n = 6. ‡p < 0.05.

All values represent the mean ± SEM. p-value in A, B and H was determined using two-tailed unpaired Student’s t-test; p-value in C, F and G was determined using one-way ANOVA coupled to a Fisher’s least-significant difference (LSD) post-hoc test.
Cathepsin A regulates chaperone‐mediated autophagy through cleavage of the lysosomal receptor (2002)
Figure 1

PPCA associates with lamp2a in rat liver lysosomes. (A) Solubilized lysosomes cross‐linked with DSP were subjected to affinity chromatography with the antibody against the cytosolic tail of lamp2a (lanes 1 and 2). Eluted proteins were subjected to SDS–PAGE and silver stained (lane 1), or immunoblotted for lamp2a (lane 2). The sequence of the N‐terminus of the 32 kDa band is shown. Part of the solubilized lysosomes were directly subjected to non‐reducing SDS–PAGE (5%) and immunoblotted for lamp2a (lane 3) or PPCA (lane 4). Arrowheads indicate lamp2a multimeric complexes. The 600 kDa (*) and 200 kDa (**) molecular weight complexes of lamp2a were excised and subjected to reducing SDS–PAGE (12%) and silver staining (lanes 5 and 6). Molecular weight (kDa) is indicated on the left. (B) Immunoblot analysis of PPCA in rat liver lysosomes, their membranes (MB) and matrices (MTX) (100 μg of protein) incubated alone (None) or with 5 mM MgCl2. Arrowheads indicate the precursor (54 kDa) and heavy chain (32 kDa) of the mature PPCA. (C) Immunoblot analysis of hsc73 (upper) and PPCA (lower) in membranes from rat liver lysosomes incubated alone (None) or with 5 mM MgCl2, CaCl2, MnCl2 or 2 mM EDTA. (D) Immunoblot analysis of lamp2a co‐immunoprecipitated with PPCA in the absence of chemical cross‐linkers from membranes of liver lysosomes incubated as in (B). Light and heavy chains of IgG are shown. Lane 1 contains 1/10 of the total amount of lysosomal membranes used for immunoprecipitation. (E) Membranes from lysosomes treated as in (D) were subjected to immunoprecipitation with an antibody specific for lamp2a or with a pre‐immune serum. Carboxypeptidase activity in total lysosomes and in the immunoprecipitates was measured as described under Materials and methods. Values are expressed as percentage of total carboxypeptidase activity in lysosomes present in the immunoprecipitates and are the mean ± SE of three different experiments.
Cathepsin A regulates chaperone‐mediated autophagy through cleavage of the lysosomal receptor (2002)
Figure 2

Levels of PPCA associated with the lysosomal membrane correlate with rates of CMA. Membranes of lysosomes incubated with increasing concentrations of GAPDH (A) or MgCl2 (B, top panel) as labeled, were analyzed by immunoblot for all forms of lamp2 (upper), lamp2a (middle) or PPCA (lower). The arrowhead indicates a previously identified truncated form of lamp2 lacking the cytosolic/transmembrane region (Cuervo and Dice, 2000b). (B, bottom panel) Chart showing the effect of increasing concentrations of MgCl2, CaCl2 or EDTA on the degradation of [14C]GAPDH by intact rat liver lysosomes. Values are means ± SE of six different experiments. Differences from the control value were significant at P 0.001 (**) or P 0.01 (*). (C) Immunoblot analysis for PPCA (upper) and cathepsin L (lower) of rat liver lysosomes (100 μg of protein) with high (H+) and low (H−) activity for CMA and of the lysosomal membranes (L.Memb) and matrices (L.Mtx) from both groups of lysosomes (200 μg of protein). (D) Immunoblot analysis for lamp2a, PPCA and cathepsin D, as labeled, of lysosomes (100 μg of protein) from fed or 48 h starved rats and the membranes (L. Memb) and matrices (L. Mtx) of both goups of lysosomes (200 μg of protein). Only mature forms of the cathepsins are shown. (E) Correlation between CMA activity, measured as in (B, bottom panel) and levels of PPCA at the lysosomal membrane determined by denstometric quantification of immunoblots similar to those shown in Figures 1 and 2 in lysosomes from fed or 20 h starved rats (Starv 20h), highly active (H+) or less active (H−) lysosomes, or lysosomes incubated with 1 mM CaCl2, MgCl2, EDTA, or increasing amounts (2, 5, 10 μg) of GAPDH. Values are expressed as times the value in fed rats (control) and are means ± SE of 3–6 different experiments.
Cathepsin A regulates chaperone‐mediated autophagy through cleavage of the lysosomal receptor (2002)
Figure 3

CMA is abnormally activated in PPCA‐deficient fibroblasts. (A) Rates of protein degradation in skin fibroblasts from wild‐type (control) or PPCA(−/−) mice maintained in the presence (serum +) or absence of serum (serum −). Values are expressed as the percentage of initially radiolabeled proteins remaining at each time and are means ± SE of four different experiments. (B) Degradation of [14C]GAPDH after 30 min incubation with lysosomes isolated from wild‐type and PPCA(−/−) mice skin fibroblasts supplemented or deprived of serum was measured as described in Material and methods. Where indicated, 25 μg of RNase A were added. Values are means ± SE of four different experiments. Differences from the control value were significant to P 0.001 (**). (C) Immunofluorescent staining for lamp2a and lamp1 of skin fibroblasts from wild‐type and PPCA(−/−) mice. Gain for lamp2a images (top) was 1/8 of the one for lamp1 (bottom) to visualize the punctate pattern of lamp2a in PPCA(−/−) mice. Inset: detail of the vesicular distribution of lamp2a. The gain in wild type was eight times the gain in PPCA(−/−) mice). Bars: 100 μm (top), 50 μm (bottom), 10 μm (inset). (D) Immunoblot analysis for lamp2a, all lamp2s, lamp1 or cathepsin D (cath D) of homogenates (75 μg of protein), lysosomes (10 μg of protein) and lysosomal membranes (L.MB) and matrices (L.MTX) (5 μg of protein) isolated from wild‐type (WT) and PPCA(−/−) skin fibroblasts. The bottom chart shows the densitometric quantification of the membrane proteins (means + SE) from four immunoblots similar to those shown here. Differences from the control value were significant to P 0.001 (**) and P 0.05 (*).
Cathepsin A regulates chaperone‐mediated autophagy through cleavage of the lysosomal receptor (2002)
Figure 4

Lamps levels in livers from PPCA(−/−) mice. (A) Immunoblot analysis for lamp2a, all lamp2s, lamp1, transferrin receptor (TFR) or cathepsin D (cath D) of liver homogenates (100 μg of protein) from wild‐type (WT), PPCA(−/−) and β‐galactosidase(−/−) (GM) mice. Right: densitometric quantification of three immunoblots (means + SE) similar to the ones shown here. Differences from the control value were significant to P 0.001 (**) and P 0.05 (*). (B) Immunocytochemistry for lamp2a (left), lamp1 (center) or lamp2s (right) in hematoxylin and eosin‐stained sections from the same livers. Bar: 50 μm. Black arrows: hepatocytes; white arrows: Kupffer cells. (C) Immunofluorescence for lamp2a (top) and P‐glycoprotein (bottom) in mouse liver sections. The right panel shows merged images. Bar: 100 μm. Inset shows detailed area at higher magnification. Bar: 50 μm.
Cathepsin A regulates chaperone‐mediated autophagy through cleavage of the lysosomal receptor (2002)
Figure 5

Impaired lamp2a degradation in PPCA‐deficient fibroblasts. (A) Autofluorography of the sequential immunoprecipitation of lamp2a first (left) and all the remaining isoforms of lamp2 second (right) from metabolically labeled wild‐type and PPCA(−/−) mouse skin fibroblasts. Values are means ± SE of three different experiments similar to the ones shown in the upper panels. (B) Immunoblot analysis for lamp2a (top) and all lamp2 isoforms (bottom) in lysosomal membranes from wild‐type (WT) or PPCA(−/−) mouse skin fibroblasts at different times after incubation at 37°C. The open arrowhead indicates the truncated form of lamp2 lacking the cytosolic/transmembrane region (Cuervo and Dice, 2000b). Right shows the densitometric quantification (mean ± SE) of four different experiments similar to the one shown here. Values are expressed as percentage of remaining lamp2a, and are means ± 1 SE of three different experiments.
Cathepsin A regulates chaperone‐mediated autophagy through cleavage of the lysosomal receptor (2002)
Figure 6

Restoration of PPCA protease activity in GS cells normalizes CMA. (A) Rates of total protein degradation in the presence and absence of serum of normal skin fibroblasts (CTR), GS cells (None) and GS cells supplemented with the precursor forms of native PPCA (+PPCA), a catalytic mutant of PPCA (+PPCA S/A) or cathepsin L (Cath L). Values are means ± SE of six different experiments. Differences from the control value were significant for P 0.001 (**) and P 0.05 (*). (B) Immunoblot analysis for lamp2a and cathepsin D (Cath D) of homogenates of wild‐type and PPCA(−/−) cells supplemented as in (A). Right: densitometric quantification (means + range of values) of two experiments similar to the one shown. Values are expressed as times the value in wild‐type cells. (C) Immunoblot analysis for lamp2a at time 0 or after 40 min incubation at 37°C of lysosomes isolated from PPCA(−/−) cells (None) and PPCA(−/−) cells supplemented as in (A). At 40 min immunoblot with the antibody against the luminal region of lamp2a is depicted to show the truncated form of lamp2a (open arrowhead). Right: densitometric quantification for lamp2a (means + range of values) of two different experiments similar to the one shown. Values are expressed as percentage of the lamp2a present in non‐supplemented cells. (D) Immunocytochemistry for lamp2a of liver (top) and kidney (bottom) sections of age‐matched wild‐type (WT), PPCA(−/−) and bone marrow transplanted (BMT) mice. Bar, 50 μm (liver) or 100 μm (kidney).
Cathepsin A regulates chaperone‐mediated autophagy through cleavage of the lysosomal receptor (2002)
Figure 7

Cleavage site of PPCA in lamp2a. (A) Left: amino acid sequences of the C‐terminal regions of lamp2a from different species and of other lamp2 isoforms and lamp1 from mouse. The proposed cleavage site for PPCA in lamp2a is highlighted. Right: immunoblot analysis for HA of lysosomal membranes isolated from two different clones of HEK293 (mouse; upper panel) and NIH 3T3 cells (human; lower panel) stably transfected with wild‐type (FL) and mutated (GL) HA‐lamp2a. The arrowhead indicates the truncated form of lamp2 lacking the cytosolic/transmembrane region. (B) Total rates of protein degradation in the presence and absence of serum in non‐transfected HEK293 cells (WT) and in the transfected HEK293 clones described in (A). Values are expressed as the percentage of initially radiolabeled proteins remaining at each time and are means ± SE of three different experiments. (C) Top: immunoblot analysis with an anti‐HA antibody of purified wild‐type (FL) and mutated (GL) mouse HA‐lamp2a incubated in an acidic pH buffer alone, or with PPCA. Bottom: wild‐type HA‐lamp2a was incubated as in the top panel without additions (None) or in the presence of 2 mM EDTA, 10 μM L‐trans‐epoxysuccinyl‐leucylamide‐(4‐guanido)‐butane (E‐64), 2 μM pepstatin A (Pepst) or 10 μM ABSF. The open arrowhead indicates the truncated form of lamp2a.
Structure and Elevator Mechanism of the Mammalian Sodium/Proton Exchanger NHE9 (2020)
Figure 1

Fig. 1. Horse NHE9 functional characterization and cryo-EM structure.

(A) Phylogenetic tree of canonical human NHE1-9 (SLC9A1-9) cluster into those that localise predominantly to either the plasma membrane (pink) or endomembrane (orange); for completeness more distantly-related non-canonical human NHE members SLC9B1-2 (NHA1-2) (yellow) and SLC9C (blue) are also shown as labelled.

(B) SEC trace and SDS-PAGE of purified NHE9* (residues 8 to and 574 out of 644) as depicted by schematic.

(C) Activity of NHE9* co-reconstituted with ATPase into liposomes to mimic the in vivo situation (schematic). Representative ACMA fluorescence traces of liposome reconstituted NHE9* (blue), NHE9* double-mutant N243A-D244A (red), and rat fructose transporter GLUT5 (black). ATP-driven H+ pumping establishes a ΔpH (0-3 min). H+ efflux is initiated by the addition of 40 mM NaCl, and subsequent addition of NH4Cl (4 min) collapses the proton gradient.

(D) Michaelis-Menten kinetics for NHE9* (red), NHE9 ΔCTD (green), N243A-D244A (blue) and rat GLUT5 (black) as detected by ACMA dequenching following substrate addition. In all experiments errors bars, s.e.m.; n = 3 technical repeats. The apparent KM values are an average from n = 3 separate protein reconstitutions.

(E) Cryo-EM density map of the NHE9 ∆CTD homodimer with the 6-TM core transport domains (coloured in blue), the dimer domain (coloured in orange), and the linker helix (coloured in grey).
Structure and Elevator Mechanism of the Mammalian Sodium/Proton Exchanger NHE9 (2020)
Figure 4

Fig. 4. Phosphoinositide-mediated stabilization of NHE9 dimer.

(A) Native mass spectrum of NHE9* purified in the presence (top panel) or the absence of additional brain lipids (bottom panel). In the presence of brain lipids, NHE9* is detected as exclusively dimeric protein with poorly resolved peaks, indicating the presence of multiple lipid adducts. Without brain lipid addition, NHE9* appears as sharp peaks, revealing several adducts of approximately 1 kDa each, as well as a minor monomer population.

(B) Thermal stabilization of purified dimeric NHE9*-GFP by lipids. Normalized mean FSEC peak fluorescence before heating (open bars), and after heating and centrifugation (grey bars) in presence of different lipids. Data presented are mean values ± data range of n = 4 experiments (see Materials and Methods).

(C) Thermal shift stabilization of purified dimeric NHE9*-GFP in the presence of PIP2 (red) compared to PIP2-free (black). Data presented are normalized mean FSEC peak fluorescence as mean values ± data range of n = 2 technical repeats; the apparent Tm was calculated with a sigmoidal 4-parameter logistic regression function; the average ΔTm presented is calculated from n = 2 independent titrations.

(D) Cartoon representation of NHE9 including a model of the loop between TM2-TM3, coloured as in Fig. 2A. The positively charged residues Lys85, Lys105 and Lys107 are shown as purple spheres.

(E) Thermal shift stabilization of the dimeric NHE9*-K85Q-K105Q-K107Q-GFP by PIP2 (red) compared with thermal shift in the absence (black) of PIP2; data shown are mean values ± data range of n = 2 technical repeats; the apparent Tm was calculated with a sigmoidal 4-parameter logistic regression function; the average ΔTm presented is calculated from n = 2 independent titrations.

(F) Native MS of the triple mutant reveals monomeric NHE9 with no notable lipid adducts; a peak highlighted by * was determined to be a soluble contaminant as it was also apparent at MS conditions where no NHE9 was retained.