sn-Glycerol-1-Phosphate-Forming Activities in Archaea: Separation of Archaeal Phospholipid Biosynthesis and Glycerol Catabolism by Glycerophosphate Enantiomers

In Methanobacterium thermoautotrophicum, sn-glycerol-1-phosphate (G-1-P) dehydrogenase is responsible for the formation of the Archaea-specific backbone of phospholipids, G-1-P, from dihydroxyacetonephosphate (DHAP). The possible G-1-P-forming activities were surveyed in cell-free extracts of six species of Archaea. All the archaeal cell-free homogenates tested revealed the ability to form G-1-P from DHAP. In addition, activities of G-3-P-forming glycerol kinase and G-3-P dehydrogenase were also detected in four heterotrophic archaea, while glycerol kinase activity was not detected in two autotrophic methanogens. These results show that G-1-P is produced from DHAP by G-1-P dehydrogenase in a wide variety of archaea while exogenous glycerol is catabolized via G-3-P.     

Isolation and characterization of the major phospholipase a2 from the venom of trimeresurus purpureomaculatus (shore pit viper)

• 1.1. The major phospholipase A₂ (PLA-DE4) of the venom of Trimeresurus purpureomaculatus (shore pit viper) has been purified to electrophoretic homogeneity.
• 2.2. The isoelectric point of the purified enzyme was determined to be 4.20, and the mol. wt was 31,700 as estimated by Sephadex G-75 gel filtration chromatography; and 14.000 as estimated by SDS-polyacrylamide gel electrophoresis.
• 3.3. The purified enzyme hydrolyzed phosphatidylcholine (PC) faster than phosphatidylethanolamine (PE), whereas phosphatidylserine (PS) was not hydrolyzed at all (PC > PE > PS = 0). However, in reaction system consisted of mixtures of PC and PS, phosphatidylserine was effectively hydrolyzed by the enzyme.
• 4.4. The phospholipase A₂ exhibited edema-forming activity but not hemolytic, hemorrhagic or anticoagulant activities. It was not lethal to mice at a dosage of 10 μg/g by i.v. route.

     

Structural and functional analysis of the three MIF4G domains of nonsense-mediated decay factor UPF2

Nonsense-mediated decay (NMD) is a eukaryotic quality control pathway, involving conserved proteins UPF1, UPF2 and UPF3b, which detects and degrades mRNAs with premature stop codons. Human UPF2 comprises three tandem MIF4G domains and a C-terminal UPF1 binding region. MIF4G-3 binds UPF3b, but the specific functions of MIF4G-1 and MIF4G-2 are unknown. Crystal structures show that both MIF4G-1 and MIF4G-2 contain N-terminal capping helices essential for stabilization of the 10-helix MIF4G core and that MIF4G-2 interacts with MIF4G-3, forming a rigid assembly. The UPF2/UPF3b/SMG1 complex is thought to activate the kinase SMG1 to phosphorylate UPF1 in vivo. We identify MIF4G-3 as the binding site and in vitro substrate of SMG1 kinase and show that a ternary UPF2 MIF4G-3/UPF3b/SMG1 complex can form in vitro. Whereas in vivo complementation assays show that MIF4G-1 and MIF4G-2 are essential for NMD, tethering assays reveal that UPF2 truncated to only MIF4G-3 and the UPF1-binding region can still partially accomplish NMD. Thus UPF2 MIF4G-1 and MIF4G-2 appear to have a crucial scaffolding role, while MIF4G-3 is the key module required for triggering NMD.     

Structural and functional organization of the photosystems in spinach chloroplasts. Antenna size,relative electron-transport capacity,and chlorophyll composition

The structural and functional organization of the spinach chloroplast photosystems (PS) I, II_α and II_β was investigated. Sensitive absorbance difference spectrophotometry in the ultraviolet (?A₃₂₀) and red (?A₇₀₀) regions of the spectrum provided information on the relative concentration of PS II and PS I reaction centers. The kinetic analysis of PS II and PS I photochemistry under continuous weak excitation provided information on the number (N) of chlorophyll (Chl) molecules transferring excitation energy to PS II_α, PS II_β and PS I. Spinach chloroplasts contained almost twice as many PS II reaction centers compared to PS I reaction centers. The number N_α of chlorophyll (Chl) molecules associated with PS II_α was 234, while N_β = 100 and N_{PS I} = 210. Thus, the functional photosynthetic unit size of PS II reaction centers was different from that of PS I reaction centers. The relative electron-transport capacity of PS II was significantly greater than that of PS I. Hence, under light-limiting green excitation when both Chl a and Chl b molecules are excited equally, the limiting factor in the overall electron-transfer reaction was the turnover of PS I. The Chl composition of PS I, PS II_α and PS II_β was analyzed on the basis of a core Chl a reaction center complex component and a Chl $\text{a}\text{b-}\text{LHC}$ component. There is a dissimilar Chl $\text{a}\text{b-}\text{LHC}$ composition in the three photosystems with 77% of total Chl b associated with PS II_α only. The results indicate that PS II_α, located in the membrane of the grana partition region, is poised to receive excitation from a wider spectral window than PS II_β and PS I.     

The thermodynamics of interaction between Sephadex and penetrating solutes

1. We have measured the partition coefficients of bovine serum albumin with Sephadex grades G-100, G-150 and G-200, and of a dextran ([unk]_n 19700) and a polyethylene glycol ([unk]_n 8000) with Sephadex G-200. We have also measured the effects of these solutes on the inner volumes of the grades of Sephadex. 2. The results can be described with fair consistency by means of a simple thermodynamic treatment that makes use of the virial coefficients of Sephadex and of the solute, and of a coefficient that expresses their interaction. This coefficient is related to the `exclusion volume' of Sephadex for the solutes. 3. The Sephadex G-200–polyethylene glycol system shows anomalies of behaviour that are ascribed to the occurrence of `incompatible' phase separation within the Sephadex beads.     

The effect of N-fertilisation rate or inclusion of red clover to timothy leys on fatty acid composition in milk of dairy cows fed a commercial silage : concentrate ratio

The aim of this experiment was to, under typical Swedish production conditions, evaluate the effects of grass silages subjected to different N-fertilisation regimes fed to dairy cows on the fatty acid (FA) composition of their milk, and to compare the grass silages in this respect to red clover-dominated silage. Grass silages made from first year Phleum pratense L. leys subjected to three N-fertilisation regimes (30, 90 and 120 kg N/ha, designated G-30, G-90 and G-120, respectively) and a mixed red clover–grass silage (Trifolium pratense L. and P. pratense L.; 60/40 on dry matter (DM) basis, designated RC–G) were produced. The experiment was conducted as a change-over design, including 24 primiparous and multiparous dairy cows of the Swedish Red breed, each of which was allocated to three of the four diets. The cows were offered 11 kg DM of silage and 7 kg concentrates. The silages had similar DM and energy concentrations. The CP concentration increased with increase in N-fertilisation level. There was a linear increase in DM intake of the different silages with increased N fertilisation. There were also differences in concentrations of both individual and total FAs amongst silages. The daily milk production (kg/day) did not significantly differ between treatments, but G-30 silage resulted in higher concentrations of 18:2n-6 in the milk compared with the other two grass silages. The highest concentrations of 18:3n-3 and cis-9, trans-11 18:2 were found in milk from cows offered the RC–G silage. The G-30 diet resulted in higher concentration of 18:2n-6 and the same concentration of 18:3n-3 in the milk as the other grass silages, despite lower intake levels of these FAs. The apparent recoveries of 18:3n-3 from feed to milk were 5.74%, 4.27%, 4.10% and 5.31% for G-30, G-90, G-120 and RC–G, respectively. A higher recovery when red clover is included in the diet confirms previous reports. The higher apparent recovery of 18:3n-3 on the G-30 treatment may be related to the lower silage DM intake, which led to a higher relative proportion of ingested FAs originating from concentrates compared with the G-90 and G-120 diets. With the rates and types of concentrates used in this study, the achieved differences in FA composition among the silages were not enough to influence the concentrations of unsaturated FAs in milk.     

High Yield Non-detergent Isolation of Photosystem I-Light-harvesting Chlorophyll II Membranes from Spinach Thylakoids: IMPLICATIONS FOR THE ORGANIZATION OF THE PS I ANTENNAE IN HIGHER PLANTS*

Styrene-maleic acid copolymer was used to effect a non-detergent partial solubilization of thylakoids from spinach. A high density membrane fraction, which was not solubilized by the copolymer, was isolated and was highly enriched in the Photosystem (PS) I-light-harvesting chlorophyll (LHC) II supercomplex and depleted of PS II, the cytochrome b₆/f complex, and ATP synthase. The LHC II associated with the supercomplex appeared to be energetically coupled to PS I based on 77 K fluorescence, P₇₀₀ photooxidation, and PS I electron transport light saturation experiments. The chlorophyll (Chl) a/b ratio of the PS I-LHC II membranes was 3.2 ± 0.9, indicating that on average, three LHC II trimers may associate with each PS I. The implication of these findings within the context of higher plant PS I antenna organization is discussed.     

Isolation and characterisation of anaerobic cellulose-degrading bacteria from East African porcupine (Hystrix cristata)

Two strains of obligately anaerobic cellulolytic bacteria designated as PS7 and PS8 (PS for porcupine species) were isolated from hindgut fluid of a crested porcupine (Hystrix cristata). The rates of cellulose degradation, total volatile fatty acids, and gas production from cellulose by the isolates were determined in comparison with Ruminococcus flavefaciens FD-1. Ruminococcus flavefaciens FD-1 degraded acid swollen cellulose and produced total volatile fatty acid at a faster rate (0.03145 mg/d; 3.8350 μmol/mL) than PS7 (0.03113 mg/d; 2.5278 μmol/mL) and PS8 (0.0125 mg/d; 2.1080 μm/mL). However, PS7 degraded cellulose strips (untreated) faster (1.5 weeks) than R. flavefaciens FD-1 (2 weeks). Furthermore, PS7 produced gas at a higher rate (0.1055 ml/d) than R. flavefaciens FD-1 (0.03145 ml/d) more produced butyric, isovaleric acids and almost twice the amounts of total volatile fatty acids from acid swollen cellulose. Both PS7 and PS8 were Gram variable, rod shaped and motile. On cellobiose medium, PS7 grew at temperature ranges from 25 to 45°C while PS8 did not grow at 25 and 45°C. Both isolates grew at pH levels between 6.2 and 11. Characterisation based on carbohydrate fermentation and morphology indicated that these two isolates were similar. Characterisation by RAPD-PCR suggested that PS7 and PS8 were genotypically similar but distinct. Phylogenetic analysis using the nucleotide sequence (1450 bp) of the 16S rRNA gene suggested that PS7 clustered with Clostridium sub-phylum and exhibited the highest similarity (95%) withClostridium lentocellum . The phylogenetic results suggest that PS7 might represent a new taxon.     

Effect of substitution of wheat starch by potato starch on the performance,digestive physiology and health of growing rabbits

The goal of this research was to study the effect of the substitution of wheat starch by potato starch (PS) on the performance, health and digestion of growing rabbits. Three experimental diets were formulated with 0%, 7% and 14% PS (PS0, PS7 and PS14, respectively) and similar starch contents (22% dry matter basis), proteins and fibre. The three diets were administered to three groups of 48 rabbits from weaning (28 days) to slaughter (70 days), and growth and health measurements were made. Another 10 rabbits per diet (30 rabbits at each age), reared under similar conditions, were slaughtered at 6 to 10 weeks of age, and the digesta were collected to analyse the caecal microbial activity (pH, volatile fatty acids (VFA) levels, fibrolytic activity) and the starch concentration in the ileal digesta. At the same ages, the whole tract digestibility coefficients were measured in 10 other rabbits for each treatment (30 rabbits). The feed intake between 28 and 42 days of age (days) increased by 11% (P < 0.05) in PS0 v. PS14. Over the whole growth period (28 to 70 days), weight gain was similar among diets (40.5 g/day), whereas the feed intake and feed conversion increased (8.5% and 5.2%, respectively; P < 0.05) with the PS14 diet. Mortality and morbidity were not affected by the diets. The starch concentration of the ileal contents increased (P < 0.01) with the addition of PS to the diet (0.39%, 0.77% and 1.08% for diets PS0, PS7 and PS14, respectively). Starch digestibility was 0.8 percentage units higher (99.8% v. 99.0%) with the PS0 diet than the PS14 diet (P = 0.04). The bacterial cellulolytic activity in the caecum tended to be higher with the PS14 diet (P = 0.07). The total VFA caecal concentration increased (P < 0.01) only in 6-week-old rabbits with PS7 compared with PS0 (54.7 v. 74.5 mmol/l). Protein digestibility and ileal starch concentration decreased (P < 0.05) with age (6 v. 10 weeks), and hemicelluloses digestibility increased (P < 0.05). At 10 weeks of age, rabbits showed a higher VFA pool (6.25 mol) and proportion of butyrate (15.9%) and a lower proportion of acetate (79.3%), ammonia level (7.5 mmol/l) and C3/C4 ratio (0.31) than at 6 weeks of age. The intake of potato starch had no effect on the performance, caecal microbial activity or digestive health of growing rabbits.     

Partial purification and characterization of membrane-bound and cytosolic phosphatidylinositol-specific phospholipases C from murine thymocytes

Membrane-bound and cytosolic phosphatidylinositol (PI)-specific phospholipases C in murine thymocytes have been partially purified and characterized. The membrane-bound enzyme was extracted from microsomes with sodium cholate and purified by sequential column chromatographies on Sephadex G-100, heparin-Sepharose CL-6B, and Sephadex G-100. The cytosolic enzyme was purified from the cytosol by sequential column chromatographies on Sephadex G-100 and FPLC-Mono S. Specific activities of the membrane-bound enzyme and the cytosolic enzyme increased more than 1,800- and 1,400-fold, respectively, compared with those of microsomes and the cytosol. The molecular weights of the both enzymes were estimated to be about 70,000 by gel filtration. These purified enzymes also hydrolyzed phosphatidylinositol 4,5-bisphosphate (PIP2). At neutral pH and low Ca2+ concentrations, the membrane-bound enzyme hydrolyzed PIP2 in preference to PI and showed higher activity than the cytosolic enzyme. These activities were also affected differently by various lipids. For PIP2 hydrolysis, all lipids investigated except lysophosphatidylcholine enhanced the activity of the membrane-bound enzyme, while phosphatidylcholine (PC) and phosphatidylserine (PS) did not significantly affect the activity of the cytosolic enzyme. PC, PE, and PS inhibited the activities of the membrane-bound and cytosolic enzymes for PI hydrolysis. The physiological implications of these results are discussed.     

A reliable method for the estimation of DNA in higher plant tissues.

A method for the isolation of the calcinogenic principle of Solanum malacoxylon is described. The procedure includes preliminary purification of an aqueous leaf extract by dialysis and treatment with ion-exchange resins. Final purification is achieved on Sephadex G-15 and G-10 columns and by paper chromatography.     

Leishmania amazonensis exhibits phosphatidylserine-dependent procoagulant activity,a process that is counteracted by sandfly saliva

Leishmania parasites expose phosphatidylserine (PS) on their surface, a process that has been associated with regulation of host''s immune responses. In this study we demonstrate that PS exposure by metacyclic promastigotes of Leishmania amazonensis favours blood coagulation. L. amazonensis accelerates in vitro coagulation of human plasma. In addition, L. amazonensis supports the assembly of the prothrombinase complex, thus promoting thrombin formation. This process was reversed by annexin V which blocks PS binding sites. During blood meal, Lutzomyia longipalpis sandfly inject saliva in the bite site, which has a series of pharmacologically active compounds that inhibit blood coagulation. Since saliva and parasites are co-injected in the host during natural transmission, we evaluated the anticoagulant properties of sandfly saliva in counteracting the procoagulant activity of L. amazonensis . Lu. longipalpis saliva reverses plasma clotting promoted by promastigotes. It also inhibits thrombin formation by the prothrombinase complex assembled either in phosphatidylcholine (PC)/PS vesicles or in L. amazonensis . Sandfly saliva inhibits factor X activation by the intrinsic tenase complex assembled on PC/PS vesicles and blocks factor Xa catalytic activity. Altogether our results show that metacyclic promastigotes of L. amazonensis are procoagulant due to PS exposure. Notably, this effect is efficiently counteracted by sandfly saliva.     

Photosystem I complexes associated with fucoxanthin-chlorophyll-binding proteins from a marine centric diatom, Chaetoceros gracilis

Diatoms occupy a key position as a primary producer in the global aquatic ecosystem. We developed methods to isolate highly intact thylakoid membranes and the photosystem I (PS I) complex from a marine centric diatom, Chaetoceros gracilis. The PS I reaction center (RC) was purified as a super complex with light-harvesting fucoxanthin-chlorophyll (Chl)-binding proteins (FCP). The super complex contained 224 Chl a, 22 Chl c, and 55 fucoxanthin molecules per RC. The apparent molecular mass of the purified FCP-PS I super complex (∼ 1000 kDa) indicated that the super complex was composed of a monomer of the PS I RC complex and about 25 copies of FCP. The complex contained menaquinone-4 as the secondary electron acceptor A₁ instead of phylloquinone. Time-resolved fluorescence emission spectra at 77 K indicated that fast (16 ps) energy transfer from a Chl a band at 685 nm on FCP to Chls on the PS I RC complex occurs. The ratio of fucoxanthin to Chl a on the PS I-bound FCP was lower than that of weakly bound FCP, suggesting that PS I-bound FCP specifically functions as the mediator of energy transfer between weakly bound FCPs and the PS I RC.     

A new mechanism for adaptation to changes in light intensity and quality in the red alga,Porphyra perforata. I. Relation to State 1—State 2 transitions

Time courses of chlorophyll fluorescence and fluorescence spectra at 77 K after various light treatments were measured in the red alga, Porphyra perforata. Photosystem (PS) I or II light (light 1 or 2) induced differences in the fluorescence spectra at 77 K. Light 2 decreased the two PS II fluorescence bands (F-685 and F-695) in parallel, while light 1 preferentially increased F-695. Light 1 and 2 also produced different effects on the activities of PS I and II. Preillumination with light 1 increased PS II activity and decreased PS I activity. However, preillumination with light 2 decreased PS II activity with no effect on PS I activity. These results show that there are at least two mechanisms that can alter the transfer of light energy in P. perforata. The dark state in this alga was found to be State 2 and light 1 induced a State 2-State 1 transition which retarded the transfer of light energy from PS II to PS I. Light 2 induced another change (which we have called a State 2-State 3 transition) that was accompanied by a change only in PS II activity.     

Degeneration of growth cones in a culture of embryonic neurons of mouse with presenilin 1 knockout

A comparative study of growth cone morphology in cultured embryonic neurons derived from wild type PS1(+/+) and knockout PS1(?/?) mice has been performed. Growth cones from wild type PS1(+/+) mice were well spread and usually formed radially continuous and regular lamellar extensions, short filopodia. In contrast, most growth cones from knockout PS1(?/?) mice collapsed after 3–4 days in culture. Summarizing these data, we suggest that PS1 plays an important role in growth cone structure by stabilizing the integrity of the cytoskeleton. The growth cone collapse may be the main reason of abnormal neuronal migration and impaired synaptic function in PS1(?/?) mice.     

Activation of GPR30 stimulates GTP-binding of Gαi1 protein to sustain activation of Erk1/2 in inhibition of prostate cancer cell growth and modulates metastatic properties

Previously, we reported that GPR30 activation by the receptor-specific, non-estrogenic ligand G-1 inhibited in vitro and in vivo growth of prostate cancer (PCa) cells via sustained Erk1/2 activation. Mechanism underlying the sustained Erk1/2 activation for PCa cell growth inhibition remains unclear. Here we report that G-1, through GPR30, activated Gαi1 proteins to sustain Erk1/2 activation but failed to activate adenylyl cyclase (AC) for cAMP production in PCa cells. The chemical-induced activation of AC-cAMP-PKA signaling attenuated Erk1/2 activity and blocked the cell growth inhibitory effects of G-1. Furthermore, PCa predominantly expressed Gαi1 proteins. Silencing of Gαi1 expression blocked the inhibitory effects of G-1 on PCa cell growth. By gene expression profiling, GPR30 activation by G-1 interfered expression of cell cycle regulators and machinery elements to modulate PCa cell growth and the RACGAP1 interactome to control metastatic properties. In this regard, we demonstrated that G-1 inhibited PCa cell migration and invasion with reduced formations of filopodia and stress fibers through a GPR30-dependent pathway. Taken together, our findings revealed the underlying mechanism for sustaining Erk1/2 activation upon GPR30 activation by G-1 in PCa cells and the GPR30-mediated pathways in controlling PCa cell growth and metastatic properties.     

Anthocyanins isolated from Hibiscus syriacus L. attenuate lipopolysaccharide-induced inflammation and endotoxic shock by inhibiting the TLR4/MD2-mediated NF-κB signaling pathway

BackgroundHibiscus syriacus L. has been used as a medicinal plant in many Asian countries. However, anti-inflammatory activity of H. syriacus L. remains unknown.PurposeThis study was aimed to investigating the anti-inflammatory effect of anthocyanin fractions from the H. syriacus L. variety Pulsae (PS) on the lipopolysaccharide (LPS)-induced inflammation and endotoxic shock.Study design and methodsMTT assay and flow cytometry analysis were performed to determine cytotoxicity of PS. RT-PCR, western blotting, and ELISA were conducted to evaluate the expression of proinflammatory mediators and cytokines. Molecular docking study predicted the binding scores and sites of PS to TLR4/MD2 complex. Immunohistochemical assay was conducted to evaluate the binding capability of PS to TLR4/MD2 and nuclear translocation of NF-κB p65. A zebrafish endotoxic shock model was used to evaluate anti-inflammatory activity of PS in vivo.ResultsPS suppressed LPS-induced nitric oxide and prostaglandin E₂ secretion concomitant with the downregulation of inducible nitric oxide synthase and cyclooxygenase-2 expression. Furthermore, PS inhibited the production of proinflammatory cytokines such as TNF-α, IL-6, and IL-12 in LPS-stimulated RAW 264.7 macrophages. Additionally, molecular docking data showed that PS mostly fit into the hydrophobic pocket of MD2 and bound to TLR4. In particular, apigenin-7-O-glucoside powerfully bound to MD2 and TLR4 via hydrogen bonding. Additionally, immunohistochemistry assay revealed that PS inhibited LPS-induced TLR4 dimerization or expression on the cell surface, which consequently decreased MyD88 recruitment and IRAK4 phosphorylation, resulting in the inhibition of NF-κB activity. PS also attenuated LPS-mediated mortality and abnormality in zebrafish larvae and diminished the recruitment of neutrophils and macrophages at the inflammatory site accompanied by the low levels of proinflammatory mediators and cytokines.ConclusionPS might be a novel immunomodulator for the effective treatment of LPS-mediated inflammatory diseases.     

Thrombotic Role of Blood and Endothelial Cells in Uremia through Phosphatidylserine Exposure and Microparticle Release

The mechanisms contributing to an increased risk of thrombosis in uremia are complex and require clarification. There is scant morphological evidence of membrane-dependent binding of factor Xa (FXa) and factor Va (FVa) on endothelial cells (EC) in vitro. Our objectives were to confirm that exposed phosphatidylserine (PS) on microparticle (MP), EC, and peripheral blood cell (PBC) has a prothrombotic role in uremic patients and to provide visible and morphological evidence of PS-dependent prothrombinase assembly in vitro. We found that uremic patients had more circulating MP (derived from PBC and EC) than controls. Additionally, patients had more exposed PS on their MPs and PBCs, especially in the hemodialysis group. In vitro, EC exposed more PS in uremic toxins or serum. Moreover, reconstitution experiments showed that at the early stages, PS exposure was partially reversible. Using confocal microscopy, we observed that PS-rich membranes of EC and MP provided binding sites for FVa and FXa. Further, exposure of PS in uremia resulted in increased generation of FXa, thrombin, and fibrin and significantly shortened coagulation time. Lactadherin, a protein that blocks PS, reduced 80% of procoagulant activity on PBC, EC, and MP. Our results suggest that PBC and EC in uremic milieu are easily injured or activated, which exposes PS and causes a release of MP, providing abundant procoagulant membrane surfaces and thus facilitating thrombus formation. Blocking PS binding sites could become a new therapeutic target for preventing thrombosis.     

Presenilin Transmembrane Domain 8 Conserved AXXXAXXXG Motifs Are Required for the Activity of the γ-Secretase Complex

Understanding the molecular mechanisms controlling the physiological and pathological activity of γ-secretase represents a challenging task in Alzheimer disease research. The assembly and proteolytic activity of this enzyme require the correct interaction of the 19 transmembrane domains (TMDs) present in its four subunits, including presenilin (PS1 or PS2), the γ-secretase catalytic core. GXXXG and GXXXG-like motifs are critical for TMDs interactions as well as for protein folding and assembly. The GXXXG motifs on γ-secretase subunits (e.g. APH-1) or on γ-secretase substrates (e.g. APP) are known to be involved in γ-secretase assembly and in Aβ peptide production, respectively. We identified on PS1 and PS2 TMD8 two highly conserved AXXXAXXXG motifs. The presence of a mutation causing an inherited form of Alzheimer disease (familial Alzheimer disease) in the PS1 motif suggested their involvement in the physiopathological configuration of the γ-secretase complex. In this study, we targeted the role of these motifs on TMD8 of PSs, focusing on their role in PS assembly and catalytic activity. Each motif was mutated, and the impact on complex assembly, activity, and substrate docking was monitored. Different amino acid substitutions on the same motif resulted in opposite effects on γ-secretase activity, without affecting the assembly or significantly impairing the maturation of the complex. Our data suggest that AXXXAXXXG motifs in PS TMD8 are key determinants for the conformation of the mature γ-secretase complex, participating in the switch between the physiological and pathological functional conformations of the γ-secretase.