Craniofacial Phenotype in Obstructive Sleep Apnea and Its Impact on Positive Airway Pressure (PAP) Adherence.

Positive airway pressure (PAP) is an important treatment tool for patients with moderate and severe obstructive sleep apnea (OSA), and adherence to PAP significantly affects treatment outcomes. Disease severity, adverse effects, and psychosocial factors are known to predict medication adherence. Cephalometric parameters have been reported to positively correlate with upper airway collapse. However, research on the correlation between these cephalometric parameters and PAP adherence remains insufficient. This study aimed to identify this relationship. This study included 185 patients with OSA who were prescribed PAP. Polysomnography (PSG) was performed to diagnose OSA, and paranasal sinus computed tomography (PNS CT) was performed to check for comorbidities of the upper airway. In addition, cephalometric parameters such as the hyoid-posterior nasal spine (H-PNS), posterior nasal spine-mandibular plane (PNS-MP), and hyoid-mandibular plane (H-MP) were measured in the midsagittal and axial CT views. Adherence was evaluated 3-12 months after the PAP prescription. A total of 136 patients were PAP-adherent, and 49 were nonadherent. There were more males in the adherent group and a higher average height in the adherent group. The PSG results showed that the apnea-hypopnea index (AHI), respiratory disturbance index (RDI), oxygen desaturation index (ODI), arousal index (AI), rapid eye movement (REM) AHI, and supine AHI were significantly higher, and the lowest oxygen saturation was lower in the adherent group. In the analysis of covariance (ANCOVA) model adjusted for sex and height, among the cephalometric parameters, H-MP was significantly longer in the adherent group (p = 0.027), and H-PNS showed a longer tendency (p = 0.074). In the logistic regression analysis model, the odds ratio (OR) and 95% confidence intervals (95% CI) of adherence and severe OSA in the third tertile compared to the first tertile of H-MP were 2.93 (1.25-6.86) and 4.00 (1.87-8.56). In the case of H-PNS, they were 2.58 (1.14-5.81) and 4.86 (2.24-10.54), respectively. This study concluded that an inferiorly placed hyoid bone in adult patients is associated with PAP adherence and disease severity.

Identification and biochemical characterization of a novel cold-adapted 1,3-α-3,6-anhydro-L-galactosidase, Ahg786, from Gayadomonas joobiniege G7.

Agar is a major polysaccharide of red algal cells and is mainly decomposed into neoagarobiose by the co-operative effort of ß-agarases. Neoagarobiose is hydrolyzed into monomers, D-galactose and 3,6-anhydro-L-galactose, via a microbial oxidative process. Therefore, the enzyme, 1,3-α-3,6-anhydro-L-galactosidase (α-neoagarobiose/neoagarooligosaccharide hydrolase) involved in the final step of the agarolytic pathway is crucial for bioindustrial application of agar. A novel cold-adapted α-neoagarooligosaccharide hydrolase, Ahg786, was identified and characterized from an agarolytic marine bacterium Gayadomonas joobiniege G7. Ahg786 comprises 400 amino acid residues (45.3 kDa), including a 25 amino acid signal peptide. Although it was annotated as a hypothetical protein from the genomic sequencing analysis, NCBI BLAST search showed 57, 58, and 59% identities with the characterized α-neoagarooligosaccharide hydrolases from Saccharophagus degradans 2-40, Zobellia galactanivorans, and Bacteroides plebeius, respectively. The signal peptide-deleted recombinant Ahg786 expressed and purified from Escherichia coli showed dimeric forms and hydrolyzed neoagarobiose, neoagarotetraose, and neoagarohexaose into 3,6-anhydro-L-galactose and other compounds by cleaving α-1,3-glycosidic bonds from the non-reducing ends of neoagarooligosaccharides, as confirmed by thin-layer chromatography and mass spectrometry. The optimum pH and temperature for Ahg786 activity were 7.0 and 15 °C, respectively, indicative of its unique cold-adapted features. The enzymatic activity severely inhibited with 0.5 mM ethylenediaminetetraacetic acid was completely restored or remarkably enhanced by Mn2+ in a concentration-dependent manner, suggestive of the dependence of the enzyme on Mn2+ ions. Km and Vmax values for neoagarobiose were 4.5 mM and 1.33 U/mg, respectively.

Toxicological evaluation of neoagarooligosaccharides prepared by enzymatic hydrolysis of agar.

Agar, a heterogeneous polymer of galactose, is the main component of the cell wall of marine red algae. It is well established as a safe, non-digestible carbohydrate in Oriental countries. Although neoagarooligosaccharides (NAOs) prepared by the hydrolysis of agar by ß-agarase have been reported to exert various biological activities, the safety of these compounds has not been reported to date. For safety evaluation, NAOs containing mainly neoagarotetraose and neoagarohexaose were prepared from agar by enzymatic hydrolysis using ß-agarase DagA from Streptomyces coelicolor. Genotoxicity tests such as the bacterial reverse mutation assay, eukaryotic chromosome aberration assay, and in vivo micronucleus assay all indicated that NAOs did not exert any mutational effects. The toxicity of NAOs in rat and beagle dog models was investigated by acute, 14-day, and 91-day repeated oral dose toxicity tests. The results showed that NAO intake of up to 5,000 mg/kg body weight resulted in no significant changes in body weight, food intake, water consumption, hematologic and blood biochemistry parameters, organ weight, or clinical symptoms. Collectively, a no-observed-adverse-effect level of 5,000 mg/kg body weight/day for both male and female rats was established for NAO. These findings support the safety of NAO for possible use in food supplements and pharmaceutical and cosmetic products.

Anti-Obesity and Anti-Diabetic Effect of Neoagarooligosaccharides on High-Fat Diet-Induced Obesity in Mice.

Neoagarooligosaccharides (NAOs), mainly comprising neoagarotetraose and neoagarohexaose, were prepared by hydrolyzing agar with ß-agarase DagA from Streptomyces coelicolor, and the anti-obesity and anti-diabetic effects of NAOs on high-fat diet (HFD)-induced obesity in mice were investigated after NAOs-supplementation for 64 days. Compared to the HFD group, the HFD-0.5 group that was fed with HFD + NAOs (0.5%, w/w) showed remarkable reduction of 36% for body weight gain and 37% for food efficiency ratios without abnormal clinical signs. Furthermore, fat accumulation in the liver and development of macrovesicular steatosis induced by HFD in the HFD-0.5 group were recovered nearly to the levels found in the normal diet (ND) group. NAOs intake could also effectively reduce the size (area) of adipocytes and tissue weight gain in the perirenal and epididymal adipose tissues. The increased concentrations of total cholesterol, triglyceride, and free fatty acid in serum of the HFD group were also markedly ameliorated to the levels found in serum of the ND group after NAOs-intake in a dose dependent manner. In addition, insulin resistance and glucose intolerance induced by HFD were distinctly improved, and adiponectin concentration in the blood was notably increased. All these results strongly suggest that intake of NAOs can effectively suppress obesity and obesity-related metabolic syndromes, such as hyperlipidemia, steatosis, insulin resistance, and glucose intolerance, by inducing production of adiponectin in the HFD-induced obese mice.

Molecular Characterization of the α-Galactosidase SCO0284 from Streptomyces coelicolor A3(2), a Family 27 Glycosyl Hydrolase.

The SCO0284 gene of Streptomyces coelicolor A3(2) is predicted to encode an α-galactosidase (680 amino acids) belonging to glycoside hydrolase family 27. In this study, the SCO0284 coding region was cloned and overexpressed in Streptomyces lividans TK24. The mature form of SCO0284 (641 amino acids, 68 kDa) was purified from culture broth by gel filtration chromatography, with 83.3-fold purification and a yield of 11.2%. Purified SCO0284 showed strong activity against p-nitrophenyl-α-D-galactopyranoside, melibiose, raffinose, and stachyose, and no activity toward lactose, agar (galactan), and neoagarooligosaccharides, indicating that it is an α-galactosidase. Optimal enzyme activity was observed at 40°C and pH 7.0. The addition of metal ions or EDTA did not affect the enzyme activity, indicating that no metal cofactor is required. The kinetic parameters Vmax and Km for p-nitrophenyl-α-D-galactopyranoside were 1.6 mg/ml (0.0053 M) and 71.4 U/mg, respectively. Thin-layer chromatography and mass spectrometry analysis of the hydrolyzed products of melibiose, raffinose, and stachyose showed perfect matches with the masses of the sodium adducts of the hydrolyzed products, galactose (M+Na, 203), melibiose (M+Na, 365), and raffinose (M+Na, 527), respectively, indicating that it specifically cleaves the α-1,6-glycosidic bond of the substrate, releasing the terminal D-galactose.

Molecular characterization of Streptomyces coelicolor A(3) SCO6548 as a cellulose 1,4-ß-cellobiosidase.

Genomic sequencing analysis and previous studies have shown that there are eight genes in Streptomyces coelicolor A3(2) encoding putative cellulases. One of these genes, sco6548, was cloned into the Streptomyces/Escherichia coli shuttle vector pUWL201PW. The recombinant protein was successfully overexpressed in S. lividans TK24 under the control of the strong ermE promoter. Sco6548 was 1740 bp in length, and encoded a 579-amino acid-, 60.8-kDa protein with strong hydrolyzing activity toward Avicel and filter paper, yielding cellobiose as the final product. SCO6548 showed optimal activity at 50°C and pH 5. The Km values of SCO6548 toward Avicel and filter paper were 15.38 and 16.1 mg/mL, respectively. The Vmax values toward Avicel and filter paper were 0.432 and 0.084 µM/min, respectively. EDTA did not affect cellulase activity; however, several divalent cations, including Co(2+), Cu(2+), Ni(2+) and Mn(2+) (at 10 mM) had severe inhibitory effects on enzyme activity. Our analysis showed that SCO6548 is a cellulose 1,4-ß-cellobiosidase that hydrolyzes cellulose into cellobiose.

Bacillus coreaensis sp. nov.: a xylan-hydrolyzing bacterium isolated from the soil of Jeju Island, Republic of Korea.

A xylan-degrading bacterium, designated as MS5(T) strain, was isolated from soil collected from the Jeju Island, Republic of Korea. Strain MS5(T) was Gram-stain-positive, aerobic, and motile by polar flagellum. The major fatty acids identified in this bacterium were iso-C15:0 (32.3%), C16:0 (27.3%), and anteiso-C15:0 (10.2%). A similarity search based on the 16S rRNA gene sequence revealed that the strain belongs to the class Bacilli and shared the highest similarity with the type strains Bacillus beringensis BR035(T) (98.7%) and Bacillus korlensis ZLC-26(T) (98.6%) which form a coherent cluster in a neighbor-joining phylogenetic tree. The DNA G+C content of strain MS5(T) was 43.0 mol%. The major menaquinone was MK-7 and the diagnostic diamino acid in the cell-wall peptidoglycan was meso-diaminopimelic acid. The DNADNA relatedness values between strain MS5(T) and two closely related species, B. beringensis BR035(T) and B. korlensis ZLC-26(T), were less than 70%. DNA-DNA relatedness analysis and 16S rRNA sequence similarity, as well as phenotypic and chemotaxonomic characteristics suggest that the strain MS5(T) constitutes a novel Bacillus species, for which the name Bacillus coreaensis sp. nov. is proposed. The type strain is MS5(T) (=DSM25506(T) =KCTC13895(T)).

Biochemical characterization of a novel iron-dependent GH16 ß-agarase, AgaH92, from an agarolytic bacterium Pseudoalteromonas sp. H9.

A putative agarase gene (agaH92) encoding a primary translation product (50.1 kDa) of 445 amino acids with a 19-amino-acid signal peptide and glycoside hydrolase 16 and RICIN superfamily domains was identified in an agarolytic marine bacterium, Pseudoalteromonas sp. H9 ( = KCTC23887). The heterologously expressed protein rAgaH92 in Escherichia coli had an apparent molecular weight of 51 kDa on SDS-PAGE, consistent with the calculated molecular weight. Agarase activity of rAgaH92 was confirmed by a zymogram assay. rAgaH92 hydrolyzed p-nitrophenyl-ß-D-galactopyranoside, but not p-nitrophenyl-α-D-galactopyranoside. The optimum pH and temperature for rAgaH92 were 6.0 and 45°C, respectively. It was thermostable and retained more than 85% of its initial activity after heat treatment at 50°C for 1 h. rAgaH92 required Fe(2+) for agarase activity and inhibition by EDTA was compensated by Fe(2+). TLC analysis, mass spectrometry and NMR spectrometry of the GST-AgaH71 hydrolysis products revealed that rAgaH92 is an endo-type ß-agarase, hydrolyzing agarose into neoagarotetraose and neoagarohexaose.

Cloning, expression, and biochemical characterization of a GH16 ß-agarase AgaH71 from Pseudoalteromonas hodoensis H7.

An agarase gene (agaH71) was identified from Pseudoalteromonas hodoensis, an agar utilizing marine bacterium. The nucleotide sequence revealed that AgaH71 had significant homology to glycosyl hydrolase (GH) 16 agarases. agaH71 encodes a primary translation product (32.7 kDa) of 290 amino acids, including a 21-amino-acid signal peptide. The entire AgaH71 was expressed in a fused protein with glutathione-S-transferase (GST) at its N-terminal (GST-AgaH71) in Escherichia coli. Purified GST-AgaH71 had an apparent molecular weight of 59 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), which was consistent with the calculated molecular weight (58.7 kDa). Agarase activity of the purified protein was confirmed by zymogram assay. GST-AgaH71 could hydrolyze p-nitrophenyl-ß-D-galactopyranoside, but not p-nitrophenyl-α-D-galactopyranoside. The optimum pH and temperature for GST-AgaH71 were 6.0 and 45 °C, respectively. GST-AgaH71 retained more than 95 and 90 % of its initial activity at 40 and 45 °C after heat treatment for 60 min, respectively. The K m and V max for agarose were 28.33 mg/ml and 88.25 U/mg, respectively. GST-AgaH71 did not require metal ions for its activity, but severe inhibition by divalent metal ions was observed. Thin-layer chromatography (TLC) analysis, mass spectrometry, and nuclear magnetic resonance (NMR) spectrometry of the GST-AgaH71 hydrolysis products revealed that GST-AgaH71 is an endo-type ß-agarase that hydrolyzes agarose into predominantly neoagarotetraose and small proportions of neoagarobiose and neoagarohexaose.

Production and characterization of a novel thermostable extracellular agarase from Pseudoalteromonas hodoensis newly isolated from the West Sea of South Korea.

A Gram-negative, aerobic, motile, rod-shaped, agarolytic bacterium, designated as H7, was isolated from a coastal seawater sample. This strain grows at pH 6.0-8.0, temperature of 15-40 °C, and at an NaCl concentration of 1-7% (w/v). Ubiquinone-8 was the predominant respiratory quinone, and the DNA G+C content was 45.82 mol%. Analysis of the 16S rRNA sequence suggests that strain H7 belongs to the genus Pseudoalteromonas. DNA-DNA hybridization analysis showed DNA relatedness of as low as 55.42 and 40.27% with its nearest phylogenetic neighbors Pseudoalteromonas atlantica IAM12927T and Pseudoalteromonas espejiana NCIMB2127T, respectively, which led us to name H7 Pseudoalteromonas hodoensis sp. nov. The type strain is H7T (=DSM25967T=KCTC23887T). An agarase (AgaA7) was purified to homogeneity from the cell-free culture broth of H7 through many steps of chromatography. Purified AgaA7 had an apparent molecular weight of 35 kDa, with a distinct NH2-terminal sequence of Ala-Asp-Ala-Thr-X-Pro (X, any amino acid) from the reported proteins, implying that it is a novel enzyme. The optimum pH and temperature for agarase activity were 7.0 and 45 °C, respectively. Thin-layer chromatography analysis, mass spectrometry, and enzyme assay using p-nitrophenyl-α/ß-D-galactopyranoside revealed that AgaA7 is both an exo- and endo-type ß-agarase that degrades agarose into neoagarotetraose, neoagarohexaose, and neoagarooctaose (minor).

Tracing lead pollution sources in abandoned mine areas using stable Pb isotope ratios.

This study focused on Pb isotope ratios of sediments in areas around an abandoned mine to determine if the ratios can be used as a source tracer. For pretreatment, sediment samples were dissolved with mixed acids, and a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS, Nu plasma II) was used to investigate the Pb isotopic composition of the samples. The measured isotope ratios were then corrected for instrumental mass fractionation by measuring the (203)Tl/(205)Tl ratio. Repeated measurements with the NIST SRM 981 reference material showed that the precision of all ratios was below 104 ppm (±2σ) for 50 ng/g. The isotope ratios ((207)Pb/(206)Pb) found were 0.85073 ± 0.0004~0.85373 ± 0.0003 for the main stream, while they were 0.83736 ± 0.0010 for the tributary and 0.84393 ± 0.0002 for the confluence. A binary mixing equation for isotope ratios showed that the contributions of mine lead to neighboring areas were up to 60%. Therefore, Pb isotope ratios can be a good source tracer for areas around abandoned mines.

Isolation and characterization of a novel agar-degrading marine bacterium, Gayadomonas joobiniege gen, nov, sp. nov., from the Southern Sea, Korea.

An agar-degrading bacterium, designated as strain G7(T), was isolated from a coastal seawater sample from Gaya Island (Gayado in Korean), Republic of Korea. The isolated strain G7(T) is gram-negative, rod shaped, aerobic, non-motile, and non-pigmented. A similarity search based on its 16S rRNA gene sequence revealed that it shares 95.5%, 90.6%, and 90.0% similarity with the 16S rRNA gene sequences of Catenovulum agarivorans YM01(T), Algicola sagamiensis, and Bowmanella pacifica W3-3A(T), respectively. Phylogenetic analyses demonstrated that strain G7(T) formed a distinct monophyletic clade closely related to species of the family Alteromonadaceae in the Alteromonas-like Gammaproteobacteria. The G+C content of strain G7(T) was 41.12 mol%. The DNA-DNA hybridization value between strain G7(T) and the phylogenetically closest strain YM01(T) was 19.63%. The genomes of G7(T) and YM01(T) had an average ANIb value of 70.00%. The predominant isoprenoid quinone of this particular strain was ubiquinone-8, whereas that of C. agarivorans YM01(T) was menaquinone-7. The major fatty acids of strain G7(T) were Iso-C15:0(41.47%), Anteiso-C15:0(22.99%), and C16:1ω7c/iso-C15:02-OH (8.85%), which were quite different from those of YM01(T). Comparison of the phenotypic characteristics related to carbon utilization, enzyme production, and susceptibility to antibiotics also demonstrated that strain G7(T) is distinct from C. agarivorans YM01T. Based on its phenotypic, chemotaxonomic, and phylogenetic distinctiveness, strain G7(T) was considered a novel genus and species in the Gammaproteobacteria, for which the name Gayadomonas joobiniege gen. nov. sp. nov. (ATCC BAA-2321 = DSM25250(T) = KCTC23721(T)) is proposed.

Channel-opening kinetic mechanism of wild-type GluK1 kainate receptors and a C-terminal mutant.

GluK1 is a kainate receptor subunit in the ionotropic glutamate receptor family and can form functional channels when expressed, for instance, in HEK-293 cells. However, the channel-opening mechanism of GluK1 is poorly understood. One major challenge to studying the GluK1 channel is its apparent low level of surface expression, which results in a low whole-cell current response even to a saturating concentration of agonist. A low level of surface expression is thought to be contributed by an endoplasmic reticulum (ER) retention signal sequence. When this sequence motif is present as in the C-terminus of wild-type GluK1-2b, the receptor is significantly retained in the ER. Conversely, when this sequence is either lacking, as in wild-type GluK1-2a (i.e., a different alternatively spliced isoform at the C-terminus), or disrupted, as in a GluK1-2b mutant (i.e., R896A, R897A, R900A, and K901A), there is a higher level of surface expression and a greater whole-cell current response. Here we characterize the channel-opening kinetic mechanism for these three GluK1 receptors expressed in HEK-293 cells by using a laser-pulse photolysis technique. Our results show that wild-type GluK1-2a, wild-type GluK1-2b, and the GluK1-2b mutant have identical channel opening and channel closing rate constants. These results indicate that the amino acid sequence near or within the C-terminal ER retention signal sequence, which affects receptor trafficking and/or expression, does not affect channel gating properties. Furthermore, as compared with the GluK2 kainate receptor, the GluK1 channel is faster to open, close, and desensitize by at least 2-fold, yet the EC(50) value of GluK1 is similar to that of GluK2.

Potent and selective inhibition of a single alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit by an RNA aptamer.

Inhibitors of AMPA-type glutamate ion channels are useful as biochemical probes for structure-function studies and as drug candidates for a number of neurological disorders and diseases. Here, we describe the identification of an RNA inhibitor or aptamer by an in vitro evolution approach and a characterization of its mechanism of inhibition on the sites of interaction by equilibrium binding and on the receptor channel opening rate by a laser-pulse photolysis technique. Our results show that the aptamer is a noncompetitive inhibitor that selectively inhibits the GluA2Q(flip) AMPA receptor subunit without any effect on other AMPA receptor subunits or kainate or NMDA receptors. On the GluA2 subunit, this aptamer preferentially inhibits the flip variant. Furthermore, the aptamer preferentially inhibits the closed-channel state of GluA2Q(flip) with a K(I) = 1.5 µM or by ∼15-fold over the open-channel state. The potency and selectivity of this aptamer rival those of small molecule inhibitors. Together, these properties make this aptamer a promising candidate for the development of water-soluble, highly potent, and GluA2 subunit-selective drugs.

Channel-opening kinetic mechanism for human wild-type GluK2 and the M867I mutant kainate receptor.

GluK2 is a kainate receptor subunit that is alternatively spliced at the C-terminus. Previous studies implicated GluK2 in autism. In particular, the methionine-to-isoleucine replacement at amino acid residue 867 (M867I) that can only occur in the longest isoform of the human GluK2 (hGluK2), as the disease (autism) mutation, is thought to cause gain-of-function. However, the kinetic properties of the wild-type hGluK2 and the functional consequence of this gain-of-function mutation at the molecular level are not well understood. To investigate whether the M867I mutation affects the channel properties of the human GluK2 kainate receptor, we have systematically characterized the rate and the equilibrium constants pertinent to channel opening and channel desensitization for this mutant and the wild-type hGluK2 receptor, along with the wild-type rat GluK2 kainate receptor (rGluK2) as the control. Our results show that the M867I mutation does not affect either the rate or the equilibrium constants of the channel opening but does slow down the channel desensitization rate by ~1.6-fold at saturating glutamate concentrations. It is possible that a consequence of this mutation on the desensitization rate is linked to facilitating the receptor trafficking and membrane expression, given the close proximity of M867 to the forward trafficking motif in the C-terminal sequence. By comparing the kinetic data of the wild-type human and rat GluK2 receptors, we also find that the human GluK2 has a ~3-fold smaller channel-opening rate constant but an identical channel-closing rate constant and thus a channel-opening probability of 0.85 vs 0.96 for rGluK2. Furthermore, the intrinsic equilibrium dissociation constant K(1) for hGluK2, like the EC(50) value, is ~2-fold lower than rGluK2. Our results therefore suggest that the human GluK2 is relatively a slowly activating channel but more sensitive to glutamate, as compared to the rat ortholog, despite the fact that the human and rat forms share 99% sequence homology.

Flip and flop: a molecular determinant for AMPA receptor channel opening.

Alternative splicing in the extracellular ligand binding domain of the AMPA receptors generates two variants, i.e., flip and flop. The flop variant of the GluR2 AMPA receptor is known to desensitize faster than the flip counterpart, whereas the GluR1 flip and flop variants exhibit the same rate of desensitization. However, whether the alternative splicing affects the channel opening kinetic properties of these receptors is unknown. Using a laser-pulse photolysis technique, we have characterized the channel opening kinetic mechanism for the flip and flop channels of GluR1 and GluR2, respectively. We find that the flop variant of GluR2 opens the channel, following the binding of glutamate, with the same rate as the flip channel, but closes its channel more rapidly. The difference in the kinetic properties between the two receptor isoforms can be described by a model we proposed previously in which the channel closing rate, a measure of the stability of the open channel state, controls an apparent tendency of the channel to desensitize, most likely, through the closed channel state. Specifically, the flop sequence of GluR2 promotes the channel to close more rapidly and consequently to desensitize with a faster rate than the flip sequence. For GluR1, the alternative splicing does not seem to affect the channel opening kinetics, since the flip and flop variants of GluR1 have the same channel opening rate, and the same channel closing rate. As expected and indeed observed, the flop variant desensitizes with the same rate as the flip variant does. On the basis of these results, we hypothesize that the flip/flop sequence cassette of AMPA receptors, in a sequence-dependent manner, regulates the rate of the channel closing process, in the microsecond time domain, through which it further regulates the channel desensitization in the millisecond time region.