[Research on quantitative evaluation of revise requirements of Specifications of Air Sampling for Hazardous Substances Monitoring in the Workplace (GBZ 159-2004)]

Objective: To conduct quantitative evaluation on the revise requirements of Specifications of Air Sampling for Hazardous Substances Monitoring in the Workplace (GBZ 159-2004) , clarify the problems and suggestions during its implementation for improvement, and provide a basis for the revision of the standard. Methods: From April to September 2021, stratified convenient sampling method was adopted and semi-open questionnaire was used to investigate the occupational health personnel in CDC, occupational prevention and control institutes, employers, third-party technical service institutions and universitie. The entropy weight of each index and the score based on entropy weight of GBZ 159 were calculated. Spearman rank correlation analysis was used to describe the correlation between the two indexes and radar chart was drawn for comprehensive evaluation. Results: A total of 151 questionnaires were received from the respondents, of which 147 were valid, with an effective recovery rate of 97.35%, involving 29 provinces, autonomous regions and municipalities. The median G scores of the necessity and urgency of GBZ 159 revision based on entropy weight were 2.84 and 3.17, respectively, and the difference was statistically significant (M=-25.50, P<0.001) . The trend of the score G of necessity and urgency based on entropy weight was basically the same for all secondary items (r(s)=0.9998, P<0.001) , and the score G of urgency based on entropy weight was higher than that of necessity. The highest score G of necessity and urgency based on entropy weight was "3.13 long time sampling", which were 7.56 and 8.23 respectively. This was followed by "3.12 short time sampling", which were 7.19 and 7.13 respectively. Conclusion: GBZ 159 has encountered some new problems and challenges in the implementation process, and some of its technical indicators have been out of line with the actual practice of occupational health at present. These are the two items that urgently needs to be revised and improved, such as "3.13 long time sampling" and "3.12 short time sampling" and other items need to be revised and improved.

[Study on the implementation effect evaluation of Specifications of Air Sampling for Hazardous Substances Monitoring in the Workplace (GBZ 159-2004)]

Systematically evaluate the implementation of Specifications of Air Sampling for Hazardous Substances Monitoring (GBZ 159-2004) , so as to provide technical basis for the future standard revision. The semi-structured interview method was used to interview the industry experts from centers for disease control and prevention, occupational disease prevention and control hospitals/institutes, employers, third-party technical service institutions and universities, and the induction method was used to refine the topics and relevant suggestions. Some technical indicators of GBZ 159 are not suitable for the current actual work of occupational health, and need to be revised and improved urgently. The revised GBZ 159 should comply with the current situation of China's industrial development and the development of occupational health testing equipment in the new era, and improve the relevant technical requirements of sampling quality control.

Molecular basis of mEAK7-mediated human V-ATPase regulation

The activity of V-ATPase is well-known to be regulated by reversible dissociation of its V1 and Vo domains in response to growth factor stimulation, nutrient sensing, and cellular differentiation. The molecular basis of its regulation by an endogenous modulator without affecting V-ATPase assembly remains unclear. Here, we discover that a lysosome-anchored protein termed (mammalian Enhancer-of-Akt-1-7 (mEAK7)) binds to intact V-ATPase. We determine cryo-EM structure of human mEAK7 in complex with human V-ATPase in native lipid-containing nanodiscs. The structure reveals that the TLDc domain of mEAK7 engages with subunits A, B, and E, while its C-terminal domain binds to subunit D, presumably blocking V1-Vo torque transmission. Our functional studies suggest that mEAK7, which may act as a V-ATPase inhibitor, does not affect the activity of V-ATPase in vitro. However, overexpression of mEAK7 in HCT116 cells that stably express subunit a4 of V-ATPase represses the phosphorylation of ribosomal protein S6. Thus, this finding suggests that mEAK7 potentially links mTOR signaling with V-ATPase activity.

[Epidemiological characteristics of local COVID-19 epidemics and control experience in routine prevention and control phase in China]

The COVID-19 pandemic is still ongoing in the world, the risk of COVID-19 spread from other countries or in the country will exist for a long term in China. In the routine prevention and control phase, a number of local COVID-19 epidemics have occurred in China, most COVID-19 cases were sporadic ones, but a few case clusters or outbreaks were reported. Winter and spring were the seasons with high incidences of the epidemics; border and port cities had higher risk for outbreaks. Active surveillance in key populations was an effective way for the early detection of the epidemics. Through a series of comprehensive prevention and control measures, including mass nucleic acid screening, close contact tracing and isolation, classified management of areas and groups at risk, wider social distancing and strict travel management, the local COVID-19 epidemics have been quickly and effectively controlled. The experiences obtained in the control of the local epidemics would benefit the routine prevention and control of COVID-19 in China. The occurrence of a series of COVID-19 case clusters or outbreaks has revealed the weakness or deficiencies in the COVID-19 prevention and control in China, so this paper suggests some measures for the improvement of the future prevention and control of COVID-19.

Molecular basis of V-ATPase inhibition by bafilomycin A1

Pharmacological inhibition of vacuolar-type H+-ATPase (V-ATPase) by its specific inhibitor can abrogate tumor metastasis, prevent autophagy, and reduce cellular signaling responses. Bafilomycin A1, a member of macrolide antibiotics and an autophagy inhibitor, serves as a specific and potent V-ATPases inhibitor. Although there are many V-ATPase structures reported, the molecular basis of specific inhibitors on V-ATPase remains unknown. Here, we report the cryo-EM structure of bafilomycin A1 bound intact bovine V-ATPase at an overall resolution of 3.6-Å. The structure reveals six bafilomycin A1 molecules bound to the c-ring. One bafilomycin A1 molecule engages with two c subunits and disrupts the interactions between the c-ring and subunit a, thereby preventing proton translocation. Structural and sequence analyses demonstrate that the bafilomycin A1-binding residues are conserved in yeast and mammalian species and the 7'-hydroxyl group of bafilomycin A1 acts as a unique feature recognized by subunit c.

[Prognostic significance of different IDH mutations and accompanying gene mutations in patients with acute myeloid leukemia]

目的

探讨IDH不同突变亚型及伴发不同基因突变在非M₃型急性髓系白血病（AML）患者中的预后意义。

方法

采用二代测序技术检测2016年6月至2018年12月就诊于郑州大学第一附属医院的389例AML患者的22种基因突变情况，通过Kaplan-Meier法及Cox回归模型分析影响预后的因素。

结果

389例AML患者中，IDH1及IDH2的突变率分别为6.2%、8.7%，未发现IDH1与IDH2共突变的情况。IDH2突变型患者年龄偏大、骨髓原始细胞比例高、正常核型多见、常合并RUNX1突变及SRSF2突变。单因素方差分析发现，IDH1突变型组较野生型组的中位总生存（OS）及无进展生存（PFS）时间明显缩短（P值均<0.05）；IDH2突变作为一个单变量对预后无显著影响，不同突变位点对预后的影响不同，IDH2R140突变对预后无显著影响，IDH2R172突变型患者较IDH2野生型患者完全缓解（CR）率明显减低、中位OS及PFS时间明显缩短（P值均<0.05）。在正常核型或年龄≥50岁的患者中，IDH不同突变亚型显示出同样的预后意义。74.1%（43/58）IDH突变患者同时携带其他基因突变，伴发基因突变数目对患者的预后无显著影响，IDH突变患者中伴NPM1突变者的CR率明显高于不伴NPM1突变者（81.8%对36.4%，P＝0.014），伴DNMT3A突变者的中位OS时间短于不伴DNMT3A突变者[4.0（95%CI 3.8～4.2）个月对6.3（95%CI 2.4～10.2）个月，P＝0.041]。多因素分析显示：年龄≥60岁、WBC≥100×10⁹/L是影响患者OS及PFS的独立危险因素，2个疗程内CR、造血干细胞移植是影响患者OS及PFS的独立有利因素。

结论

在AML（非M₃型）患者中，IDH基因突变常与其他基因突变共存，IDH不同突变亚型及伴发基因突变显示出不同的预后意义。

Cryo-EM structures of intact V-ATPase from bovine brain

The vacuolar-type H⁺-ATPases (V-ATPase) hydrolyze ATP to pump protons across the plasma or intracellular membrane, secreting acids to the lumen or acidifying intracellular compartments. It has been implicated in tumor metastasis, renal tubular acidosis, and osteoporosis. Here, we report two cryo-EM structures of the intact V-ATPase from bovine brain with all the subunits including the subunit H, which is essential for ATPase activity. Two type-I transmembrane proteins, Ac45 and (pro)renin receptor, along with subunit c", constitute the core of the c-ring. Three different conformations of A/B heterodimers suggest a mechanism for ATP hydrolysis that triggers a rotation of subunits DF, inducing spinning of subunit d with respect to the entire c-ring. Moreover, many lipid molecules have been observed in the Vo domain to mediate the interactions between subunit c, c", (pro)renin receptor, and Ac45. These two structures reveal unique features of mammalian V-ATPase and suggest a mechanism of V1-Vo torque transmission.

[Clinical features and prognostic factors in adult acute myeloid leukemia patients with FLT3-ITD and CEBPA gene co-mutation]

目的

研究FLT3-ITD及CEBPA双等位基因突变(CEBPAdm)共突变成人急性髓系白血病(AML)患者的临床特征及预后。

方法

对2016年1月至2018年9月就诊于郑州大学第一附属医院的初治成人AML患者的临床资料进行回顾性研究，比较分析其临床特点及预后。基因突变检测采用直接测序法。

结果

①接受基因突变检测的非M₃且资料完整患者599例，检出FLT3-ITD基因突变阳性（FLT3-ITD⁺）且CEBPAdm阳性（CEBPAdm⁺）患者19例（A组），FLT3-ITD⁺且CEBPAdm⁻患者84例（B组），FLT3-ITD⁻且CEBPAdm⁺患者95例（C组），未检出任何已知基因突变患者70例（D组），共计268例。②A、B、C、D四组间性别、PLT、FAB分型、诱导治疗方案、融合基因突变情况差异均无统计学意义（P值均>0.05）；而发病年龄、初诊时WBC、HGB含量、外周血原始幼稚细胞比例、骨髓原始幼稚细胞比例差异均有统计学意义（P值均<0.05）。组间两两比较，A组较B、C、D组性别、年龄、HGB含量、PLT、FAB分型差异无统计学意义（P值均>0.05）。A组初诊时外周血WBC、外周血原始幼稚细胞比例、首疗程诱导治疗后微小残留病（MRD）水平高于B、C、D各组。③A、B、C、D组首疗程化疗后完全缓解（CR₁）率分别为50.0%、32.4%、59.8%、39.0%（P=0.003），复发率分别为55.6%、50.0%、21.1%、40.0%（P<0.001），中位总生存时间分别为6.25、3.0、15.5、10.5个月（P<0.001），中位无进展生存时间分别为5.0、4.0、10.0、6.7个月（P=0.032）。

结论

FLT3-ITD及CEBPAdm共突变成人AML患者初诊时外周血WBC高，外周血原始幼稚细胞比例高，首疗程诱导化疗后MRD水平高，CR₁率低，复发率高，中位总生存时间、中位无进展生存时间短，预后不佳。

Transient Receptor Potential V Channels Are Essential for Glucose Sensing by Aldolase and AMPK

Fructose-1,6-bisphosphate (FBP) aldolase links sensing of declining glucose availability to AMPK activation via the lysosomal pathway. However, how aldolase transmits lack of occupancy by FBP to AMPK activation remains unclear. Here, we show that FBP-unoccupied aldolase interacts with and inhibits endoplasmic reticulum (ER)-localized transient receptor potential channel subfamily V, inhibiting calcium release in low glucose. The decrease of calcium at contact sites between ER and lysosome renders the inhibited TRPV accessible to bind the lysosomal v-ATPase that then recruits AXIN:LKB1 to activate AMPK independently of AMP. Genetic depletion of TRPVs blocks glucose starvation-induced AMPK activation in cells and liver of mice, and in nematodes, indicative of physical requirement of TRPVs. Pharmacological inhibition of TRPVs activates AMPK and elevates NAD+ levels in aged muscles, rejuvenating the animals' running capacity. Our study elucidates that TRPVs relay the FBP-free status of aldolase to the reconfiguration of v-ATPase, leading to AMPK activation in low glucose.

[The Role of TSP-1-CD47 in ROS-mediated Pulmonary Fibrosis Induced by Paraquat]

Objective: Taking human A549 cells as the research object, to construct the paraquat-induced pulmonary fibrosis model in vitro, and to explore the role of TSP-1 (Thrombospondin-1, TSP-1) and its receptor CD47 in PQ-induced pulmonary fibrosis. Methods: Human A549 cells were cultured in vitro, divided into normal control group, PQ group, Anti-TSP1 group (PQ with neutralizing anti-TSP1 antibody at a final concentration of 10 μg/ml) . A549 cells were stimulated with different concentrations (50, 100, 200, 400, 600, 800, 1 000 μmol/L) for different time (12, 24, 48 h) , and then CCK8 method was used to detect the cell viability to screen out the concentration and time of half cell viability. The subsequent test will be performed at this concentration point.The morphology of the cells was observed under inverted microscope. The expression levels of Fibronectin (FN) and type I collagen were determined by Enzyme Linked Immunosorbent Assay (ELISA) . Immunocytochemistry (ICC) and Immunofluorescence (IF) were used to observe the expression of TSP-1 and CD47 protein and the co-expression.The mRNA expression of TSP-1 and CD47 was detected by Real Time PCR (RT-PCR) . The protien expression of TSP-1 and CD47 was detected by Western Blot (WB) . The levels of Reactive Oxygen Species (ROS) were measured by flow cytometry. Results: Before neutralizing anti-TSP1 antibody intervention: (1) When the time of PQ was constant, the cell viability decreased with the increase of PQ concentration. (2) The cells in the control group were closely connected, cobble-like, arranged neatly; with the increase of PQ concentration, the cell gap of PQ group gradually increased, spindle shape or long spindle shape. (3) With the increase of PQ concentration, the relative expression of FN and I collagen in PQ group was gradually increased compared with the control group in a concentration-dependent manner, and 200 μmol/L is the most obvious. (4) Compared with the control group, the mRNA level and the protein expression of TSP-1 and CD47 in PQ group was significantly increased, and 200 μmol/L is the most obvious, and Immunofluorescence showed they were co-expression in cytoplasm. (5) Compared with the normal group, the level of ROS in A549 cells was significantly increased at 24 h after PQ stimulation. (6) Compared with PQ group, the cell viability of Anti-TSP1 group was significantly increased, and the morphology changed to normal cell morphology, and the mRNA level and the protein expression of TSP-1 and CD47 decreased, and the overexpression of ROS was inhibited, and the relative expression of FN and I collagen decreased. Conclusion: PQ stimulation induced morphological changes of A549 cells, increased expression of TSP-1, CD47, FN and type I collagen, and increased production of ROS.Neutralizing anti-TSP1 antibodies against TSP-1 can partially improve the above lesions. TSP-1-CD47 may be associated with oxidative stress-mediated PQ-induced pulmonary fibrosis.

[The roles of TSP-1 and its receptor CD47 in pathogenesis of paraquat-induced pulmonary fibrosis in rats]

Objective: To establish a rat model of paraquat (PQ) -induced pulmonary fibrosis and observe the changes in thrombospondin-1 (TSP-1) and its receptor CD47 in lung tissue, and to investigate their roles in the pathogenesis of PQ-induced pulmonary fibrosis. Methods: Fifty-four clean adult male Sprague-Dawley rats were randomly divided into normal control group (n=6) and 2 h, 12 h, 1 d, 3 d, 7 d, and 14 d PQ poisoning groups (n=8 per group). A rat model of PQ poisoning was established by a single gavage of 20 wt.% PQ solution (50 mg/kg). Flow cytometry was used to determine the concentration of reactive oxygen species (ROS) in blood and lung tissue. Enzyme-linked immunosorbent assay was used to determine the concentrations of hydroxyl radicals, malondialdehyde, and hydroxyproline in lung tissue. HE staining and Masson staining were used to observe the pathological damage of lung tissue after PQ poisoning. The expression of TSP-1 and CD47 in lung tissue was measured by Immunohistochemistry. Results: Compared with the normal control group, the 2 h to 7 d PQ poisoning groups showed significant increases in ROS fluorescence intensity in red blood cells and lung tissues and the concentrations of malondialdehyde and hydroxyl radicals in lung tissue (P<0.05) , and the 14 d PQ poisoning group had a significant increase in the concentration of hydroxyproline in lung tissue (P<0.05). HE staining showed that the 2 h to 7 d PQ poisoning groups had significantly higher semiquantitative pathological scores of pulmonary alveolitis than the normal control group (P<0.05). The Masson staining showed that the 7 d and 14 d PQ poisoning groups had significantly higher semiquantitative pathological scores of pulmonary fibrosis than the normal control group (P<0.05). Compared with the normal control group, all PQ poisoning groups (except the 12 h group) had significantly increased expression of TSP-1 in lung tissue (P<0.05) , and all PQ poisoning groups (except the 1 d group) had significantly increased expression of CD47 in lung tissue (P<0.05). Within 2 h after PQ poisoning, the expression of TSP-1 and CD47 was positively correlated with the concentrations of ROS, hydroxyl radicals, and malondialdehyde and the degree of pulmonary alveolitis (P<0.01) ; at 1 d after PQ poisoning, the expression of TSP-1 and CD47 was positively correlated with the concentration of hydroxyproline in lung tissue (P<0.01) . Conclusion: The expression of TSP-1 and CD47 is closely related to oxidative stress and subsequent pulmonary fibrosis, and they may be involved in the development and progression of pulmonary alveolitis and subsequent pulmonary fibrosis in rats with PQ poisoning.

[Measurement and analysis of hand-transmitted vibration of vibration tools in workplace for automobile casting and assembly]

OBJECTIVE

To investigate the features of hand-transmitted vibration of common vibration tools in the workplace for automobile casting and assembly.

METHODS

From September to October, 2014, measurement and spectral analysis were performed for 16 typical hand tools(including percussion drill, pneumatic wrench, grinding machine, internal grinder, and arc welding machine) in 6 workplaces for automobile casting and assembly according to ISO 5349-1-2001 Mechanical vibration-Measurement and evaluation of human exposure to hand-transmitted vibration-part 1: General requirements and ISO 5349-2-2001 Mechanical vibration-Measurement and evaluation of human exposure to hand-transmitted vibration-Part 2: Practical guidance for measurement in the workplace.

RESULTS

The vibration acceleration waveforms of shearing machine, arc welding machine, and pneumatic wrench were mainly impact wave and random wave, while those of internal grinder, angle grinder, percussion drill, and grinding machine were mainly long-and short-period waves. The daily exposure duration to vibration of electric wrench, pneumatic wrench, shearing machine, percussion drill, and internal grinder was about 150 minutes, while that of plasma cutting machine, angle grinder, grinding machine, bench grinder, and arc welding machine was about 400 minutes. The range of vibration total value(ahv) was as follows: pneumatic wrench 0.30~11.04 m/s(2), grinding wheel 1.61~8.97 m/s(2), internal grinder 1.46~8.70 m/s(2), percussion drill 11.10~14.50 m/s(2), and arc welding machine 0.21~2.18 m/s(2). The workers engaged in cleaning had the longest daily exposure duration to vibration, and the effective value of 8-hour energy-equivalent frequency-weighted acceleration for them[A(8)] was 8.03 m/s(2), while this value for workers engaged in assembly was 4.78 m/s(2). The frequency spectrogram with an 1/3-time frequency interval showed that grinding machine, angle grinder, and percussion drill had a high vibration acceleration, and the vibration limit curve was recommended for those with a frequency higher than 400 min/d.

CONCLUSION

The workers who are engaged in cleaning, grinding, and a few positions of assembly and use grinding machine, angle grinder, internal grinder, and percussion drill are exposed to vibrations with a high vibration acceleration and at a high position of the frequency spectrum. The hand-transmitted vibration in the positions of cutting, polishing, and cleaning in automobile casting has great harm, and the harm caused by pneumatic wrench in automobile assembly should be taken seriously.

A new dimeric anthraquinone from endophytic Talaromyces sp. YE3016

A new unsymmetrical dimeric anthraquinone, 3-demethyl-3-(2-hydroxypropyl)-skyrin (1) was isolated from the solid-state fermentation extract of an endophytic fungal strain Talaromyces sp. YE 3016, together with five known compounds, skyrin (2), oxyskyrin (3), emodin (4), 1,3,6-trihydroxy-8-methyl-anthraquinone (5) and ergosterol (6). The structure of the new compound was elucidated on the basis of spectroscopic analysis. Compounds 1-3 exhibited moderate cytotoxic activities against MCF-7 cell line.

Synthesis and structure-activity studies of the V-ATPase inhibitor saliphenylhalamide (SaliPhe) and simplified analogs

An efficient total synthesis of the potent V-ATPase inhibitor saliphenylhalamide (SaliPhe), a synthetic variant of the natural product salicylihalamide A (SaliA), has been accomplished aimed at facilitating the development of SaliPhe as an anticancer and antiviral agent. This new approach enabled facile access to derivatives for structure-activity relationship studies, leading to simplified analogs that maintain SaliPhe's biological properties. These studies will provide a solid foundation for the continued evaluation of SaliPhe and analogs as potential anticancer and antiviral agents.

Two new butenolides produced by an Actinomycete Streptomyces sp

Two new butenolides, (4S)-4,10-dihydroxydodec-2-en-1,4-olide (1) and (4S)-4,8,10-trihydroxy-10-methyldodec-2-en-1,4-olide (2), together with three known compounds, MKN-003B (3), MKN-003C (4), and cyclo(Ala-Leu) (5), were isolated from the culture broth of a bacterium of the genus Streptomyces derived from soil environment. The structures of these compounds were elucidated on the basis of spectroscopic analysis. The inhibitory activities of the butenolides against eight pathogenic fungi were evaluated. All of the butenolides showed moderate-or-weak antifungal activities in a broth microdilution assay.

Relative roles of ABCG5/ABCG8 in liver and intestine

ABCG5 (G5) and ABCG8 (G8) form a sterol transporter that acts in liver and intestine to prevent accumulation of dietary sterols. Mutations in either G5 or G8 cause sitosterolemia, a recessive disorder characterized by sterol accumulation and premature coronary atherosclerosis. Hepatic G5G8 mediates cholesterol excretion into bile, but the function and relative importance of intestinal G5G8 has not been defined. To determine the role of intestinal G5G8, we developed liver-specific (L-G5G8(-/-)), intestine-specific (I-G5G8(-/-)), and total (G5G8(-/-)) KO mice. Tissue levels of sitosterol, the most abundant plant sterol, were >90-fold higher in G5G8(-/-) mice than in WT animals. Expression of G5G8 only in intestine or only in liver decreased tissue sterol levels by 90% when compared with G5G8(-/-) animals. Biliary sterol secretion was reduced in L-G5G8(-/-) and G5G8(-/-) mice, but not in I-G5G8(-/-) mice. Conversely, absorption of plant sterols was increased in I-G5G8(-/-) and G5G8(-/-) mice, but not in L-G5G8(-/-) mice. Reverse cholesterol transport, as assessed from the fraction of intravenously administered (3)H-cholesterol that appeared in feces, was reduced in G5G8(-/-), I-G5G8(-/-), and L-G5G8(-/-) mice. Thus, G5G8 expression in both the liver and intestine protects animals from sterol accumulation, and intestinal G5G8 contributes to extrahepatic cholesterol efflux in mice.

Incomplete distal renal tubular acidosis from a heterozygous mutation of the V-ATPase B1 subunit

Congenital distal renal tubular acidosis (RTA) from mutations of the B1 subunit of V-ATPase is considered an autosomal recessive disease. We analyzed a distal RTA kindred with a truncation mutation of B1 (p.Phe468fsX487) previously shown to have failure of assembly into the V1 domain of V-ATPase. All heterozygous carriers in this kindred have normal plasma HCO3- concentrations and thus evaded the diagnosis of RTA. However, inappropriately high urine pH, hypocitraturia, and hypercalciuria were present either individually or in combination in the heterozygotes at baseline. Two of the heterozygotes studied also had inappropriate urinary acidification with acute ammonium chloride loading and an impaired urine-blood Pco2 gradient during bicarbonaturia, indicating the presence of a H+ gradient and flux defects. In normal human renal papillae, wild-type B1 is located primarily on the plasma membrane, but papilla from one of the heterozygote who had kidney stones but not nephrocalcinosis showed B1 in both the plasma membrane as well as diffuse intracellular staining. Titration of increasing amounts of the mutant B1 subunit did not exhibit negative dominance over the expression, cellular distribution, or H+ pump activity of wild-type B1 in mammalian human embryonic kidney-293 cells and in V-ATPase-deficient Saccharomyces cerevisiae. This is the first demonstration of renal acidification defects and nephrolithiasis in heterozygous carriers of a mutant B1 subunit that cannot be attributable to negative dominance. We propose that heterozygosity may lead to mild real acidification defects due to haploinsufficiency. B1 heterozygosity should be considered in patients with calcium nephrolithiasis and urinary abnormalities such as alkalinuria or hypocitraturia.

Bioactive Metabolites Produced by the Endophytic Fungus Phomopsis sp. YM355364

A new compound, 16-acetoxycytosporone B (1), along with four known ones, dankasterone A (2), dankasterone B (3), 3β,5α,9α-trihydroxy-(22E,24R)-ergosta-7,22-dien-6-one (4), and cyclonerodiol oxide (5), were isolated from Phomopsis sp. YM355364, an endophytic fungus of Aconitum carmichaeli. Their structures were characterized by spectral analysis. Compound 2 exhibited significant inhibitory activity against influenza A/Thailand/Kan353/2004(H5N1) pseudovirus with an IC50 value of 3.56 μM. Compounds 1, 2, and 4 showed either moderate or weak antifungal activities against four pathogenic fungi.

Bioactive metabolites produced by the endophytic fungus Phomopsis sp. YM355364

A new compound, 16-acetoxycytosporone B (1), along with four known ones, dankasterone A (2), dankasterone B (3), 3beta,5alpha,9alpha-trihydroxy-(22E,24R)-ergosta-7,22-dien-6-one (4), and cyclonerodiol oxide (5), were isolated from Phomopsis sp. YM355364, an endophytic fungus of Aconitum carmichaeli. Their structures were characterized by spectral analysis. Compound 2 exhibited significant inhibitory activity against influenza A/Thailand/Kan353/2004(H5N1) pseudovirus with all IC50 value of 3.56 microM. Compounds 1, 2, and 4 showed either moderate or weak antifungal activities against four pathogenic fungi.

Sequences in the nonconsensus nucleotide-binding domain of ABCG5/ABCG8 required for sterol transport

ATP-binding cassette transporters ABCG5 (G5) and ABCG8 (G8) form a heterodimer that transports cholesterol and plant sterols from hepatocytes into bile. Mutations that inactivate G5 or G8 cause hypercholesterolemia and premature atherosclerosis. We showed previously that the two nucleotide-binding domains (NBDs) in the heterodimer are not functionally equivalent; sterol transport is abolished by mutations in the consensus residues of NBD2 but not of NBD1. Here, we examined the structural requirements of NBD1 for sterol transport. Substitutions of the D-loop aspartate and Q-loop glutamine in either NBD did not impair sterol transport. The H-loop histidine of NBD2 (but not NBD1) was required for sterol transport. Exchange of the signature motifs between the NBDs did not interfere with sterol transport, whereas swapping the Walker A, Walker B, and signature motifs together resulted in failure to transport sterols. Selected substitutions within NBD1 altered substrate specificity: transport of plant sterols by the heterodimer was preserved, whereas transport of cholesterol was abolished. In summary, these data indicate that NBD1, although not required for ATP hydrolysis, is essential for normal function of G5G8 in sterol transport. Both the position and structural integrity of NBD2 are essential for sterol transport activity.

Chemically specific imaging of cryptosporidium oocysts using coherent anti-Stokes Raman scattering (CARS) microscopy

We demonstrate the application of coherent anti-Stokes Raman scattering microscopy for the rapid, label-free chemical imaging of waterborne pathogens. Chemically selective images of cryptosporidium were acquired in just a few seconds using coherent anti-Stokes Raman scattering microscopy, demonstrating its capability for the rapid detection of cryptosporidium at the single oocyst level. We discuss the applicability of such a technique in a near-real time automated water testing system.

Purification and reconstitution of sterol transfer by native mouse ABCG5 and ABCG8

ABCG5 (G5) and ABCG8 (G8) are ATP-binding cassette half-transporters that limit intestinal uptake and promote biliary secretion of neutral sterols. Here, we describe the purification of endogenous G5G8 from mouse liver to near homogeneity. We incorporated the native proteins into membrane vesicles and reconstituted sterol transfer. Native gel electrophoresis, density-gradient ultracentrifugation, and chemical cross-linking studies indicated that the functional native complex is a heterodimer. No higher order oligomeric forms were observed at any stage in the catalytic cycle. Sterol transfer activity by purified native G5G8 was stable, stereospecific, and selective. We also report that G5 but not G8 is S-palmitoylated and that palmitoylation is not essential for dimerization, trafficking, or biliary sterol secretion. Both G5 and G8 have short but highly conserved cytoplasmic tails. The functional roles of these C-terminal regions were examined using an in vivo functional assay.

Adaptive optics for enhanced signal in CARS microscopy

We report the use of adaptive optics with coherent anti-Stokes Raman scattering (CARS) microscopy for label-free deep tissue imaging based on molecular vibrational spectroscopy. The setup employs a deformable membrane mirror and a random search optimization algorithm to improve signal intensity and image quality at large sample depths. We demonstrate the ability to correct for both system and sample-induced aberrations in test samples as well as in muscle tissue in order to enhance the CARS signal. The combined system and sample-induced aberration correction increased the signal by an average factor of approximately 3x for the test samples at a depth of 700 microm and approximately 6x for muscle tissue at a depth of 260 microm. The enhanced signal and higher penetration depth offered by adaptive optics will augment CARS microscopy as an in vivo and in situ biomedical imaging modality.

Three-dimensional imaging of chemical bond orientation in liquid crystals by coherent anti- Stokes Raman scattering microscopy

Liquid crystals are a class of industrially important materials whose optical properties make them useful particularly in display technology. Optical imaging of these materials provides information about their structure and physical properties. Coherent anti-Stokes Raman scattering (CARS) microscopy is used to provide three-dimensional chemical maps of liquid crystalline samples without the use of external labels. CARS is an optical imaging technique that derives contrast from Raman-active molecular vibrations in the sample. Compared to many other three-dimensional imaging techniques, CARS offers more rapid chemical characterization without the use of external dyes or contrast agents. The use of CARS to image chemical and orientational order in liquid crystals is demonstrated using several examples, and the limitations and benefits are discussed.

Structural properties of the proton translocating complex of the clathrin-coated vesicle

The clathrin-coated vesicle proton pump is a representative member of the new class of endomembrane proton ATPases that share an inhibitor profile which distinguishes them from classic F1F0 and E1E2-type proton pumps. The coated vesicle proton pump is a large (530 kDa) heteroligomer composed of eight polypeptides with molecular masses of 116, 70, 58, 40, 38, 34, 33 and 17 kDa. The 200-fold purified enzyme catalyses ATP-generated proton pumping when reconstituted in liposomes composed of pure lipids. Subunit function has been determined by partial reaction analysis of subunit and subcomplex activities. The isolated 17 kDa subunit, when co-reconstituted with bacteriorhodopsin, forms a dicyclohexylcarbodiimide-inhibitable proton channel. Selective removal of the 116 kDa subunit transforms the proton ATPase from a Mg2+-activatable to a Ca2+-activatable ATPase. Subsequent dissociation and reconstitution of subunits reveals that the 70, 58, 40 and 33 kDa components are required, in composite, to form a functional ATP-hydrolytic core, and that no single subunit or subcomplex deficient in these subunits can catalyse ATP hydrolysis.

Three-dimensional reconstruction of bovine brain V-ATPase by cryo-electron microscopy and single particle analysis

Bovine V-ATPase from brain clathrin-coated vesicles was investigated by cryo-electron microscopy and single particle analysis. Our studies revealed great flexibility of the central linker region connecting V1 and V0. As a consequence, the two sub-complexes were processed separately and the resulting volumes were merged computationally. We present the first three-dimensional (3D) map of a V-ATPase obtained from cryo-electron micrographs. The overall resolution was estimated 34A by Fourier shell correlation (0.5 cutoff). Our 3D reconstruction shows a large peripheral stalk and a smaller, isolated peripheral density, suggesting a second, less well-resolved peripheral connection. The 3D map reveals new features of the large peripheral stator and of the collar-like density attached to the membrane domain. Our analyses of the membrane domain indicate the presence of six proteolipid subunits. In addition, we could localize the V0 subunit a flanking the large peripheral stalk.

Phase manipulated multi-beam holographic lithography for tunable optical lattices

We present principle and technique to actively stabilize and control the phase differences between multi-laser beams that produce stable and adjustable intensity patterns. This technique is based on a novel optical set-up and on a closed loop control over the phase difference between each pair of the input laser fields. Tunable optical lattices are demonstrated by exciting FeTPPCl-doped liquid crystals with the variable intensity patterns.

C. elegans mitochondrial factor WAH-1 promotes phosphatidylserine externalization in apoptotic cells through phospholipid scramblase SCRM-1

Externalization of phosphatidylserine, which is normally restricted to the inner leaflet of plasma membrane, is a hallmark of mammalian apoptosis. It is not known what activates and mediates the phosphatidylserine externalization process in apoptotic cells. Here, we report the development of an annexin V-based phosphatidylserine labelling method and show that a majority of apoptotic germ cells in Caenorhabditis elegans have surface-exposed phosphatidylserine, indicating that phosphatidylserine externalization is a conserved apoptotic event in worms. Importantly, inactivation of the gene encoding either the C. elegans apoptosis-inducing factor (AIF) homologue (WAH-1), a mitochondrial apoptogenic factor, or the C. elegans phospholipid scramblase 1 (SCRM-1), a plasma membrane protein, reduces phosphatidylserine exposure on the surface of apoptotic germ cells and compromises cell-corpse engulfment. WAH-1 associates with SCRM-1 and activates its phospholipid scrambling activity in vitro. Thus WAH-1, after its release from mitochondria during apoptosis, promotes plasma membrane phosphatidylserine externalization through its downstream effector, SCRM-1.

Sterol transfer by ABCG5 and ABCG8: in vitro assay and reconstitution

ATP-binding cassette transporters G5 and G8 are half-transporters expressed on the apical membranes of enterocytes and hepatocytes that limit intestinal uptake and promote secretion of neutral sterols. Genetic defects that inactivate either half-transporter cause accumulation of cholesterol and plant sterols, resulting in premature coronary atherosclerosis. These observations suggest that G5 and G8 promote the translocation of sterols across membranes, but the primary transport substrate of the G5G8 complex has not been directly determined. Here we report the development of a sterol transfer assay using "inside-out" membrane vesicles from Sf9 cells expressing recombinant mouse G5 and G8. Radiolabeled cholesterol or sitosterol was transferred from donor liposomes to G5- and G8-containing membrane vesicles in an ATP-dependent and vanadate-sensitive manner; net transfer of cholesterol was associated with an increase in vesicular cholesterol mass. CTP, GTP, and UTP, as well as ATP, supported transfer but with lesser efficiency (ATP >> CTP > GTP > UTP). Transfer was specific for sterols and was stereoselective; minimal ATP-dependent and vanadate-sensitive transfer of cholesteryl oleate, phosphatidylcholine, or enantiomeric cholesterol was observed. These studies indicate that G5 and G8 are sufficient for reconstitution of sterol transfer activity in vitro and provide the first demonstration that sterols are direct transport substrates of the G5 and G8 heterodimer.

Towards CARS Endoscopy

We provide a proof-of-principle demonstration of CARS endoscopy. The design utilizes a single mode optical fiber with a focusing unit attached to the distal end. Picosecond pump and Stokes pulse trains in the near infrared are delivered through the fiber with nearly unaltered spectral and temporal characteristics at intensities needed for endoscopy. CARS endoscopic images are recorded by collecting the epi-CARS signal generated at the sample and raster scanning the sample with respect to the fiber. This CARS endoscope prototype represents an important step towards in situ chemically selective imaging for biomedical applications.

Selective expression of vacuolar H+-ATPase subunit d2 by particular subsets of dendritic cells among leukocytes

Dendritic cells (DC) are far more potent to activate T cells than other antigen presenting cells (e.g., macrophages) and distributed to many organs where DC develop to functionally and phenotypically distinctive subsets. To isolate DC-differentially expressed genes, we used a subtractive cDNA cloning (XS52 DC minus J774 macrophages), resulting in the identification of d2 isoform of vacuolar (V) H+-ATPase subunit d. Unlike the ubiquitously expressed isoform (d1), d2 mRNA manifested expression restricted to particular subsets of DC (e.g., skin- and bone marrow-derived DC) among leukocytes and encoded two transcripts (1.6 and 3.0 kb) that differed in the length of the 3'-untranslated region. The d2 protein displayed association with membranes and the localization in lysosomes and antigen-containing endosomes. Interestingly, XS52 DC expressed seven-fold higher V-ATPase proton-pump activity than J774 macrophages and distinguished from the macrophage by high levels of isoforms a1 and a2 expression among V-ATPase subunits. These results indicated that d2 is a new marker for DC and it may, co-operatively with subunit a isoforms, regulate V-ATPase activity.

Chemical genetic screening identifies sulfonamides that raise organellar pH and interfere with membrane traffic

Chemical genetics seeks to identify small molecules that afford functional dissection of cell biological pathways. Previous screens for small molecule inhibitors of exocytic membrane traffic yielded the identification and characterization of several compounds that block traffic from the Golgi to the cell surface as well as transport from the endoplasmic reticulum to the Golgi network [Feng et al. Proc Natl Acad Sci USA 2003;100:6469-6474; Yarrow et al. Comb Chem High Throughput Screen 2003;6:279-286; Feng et al. EMBO Reports 2004: in press]. Here, we screened these inhibitors for potential effects on endocytic membrane traffic. Two structurally related sulfonamides were found to be potent and reversible inhibitors of transferrin-mediated iron uptake. These inhibitors do not block endoplasmic reticulum-to-Golgi transport, but do disrupt Golgi-to-cell surface traffic. The compounds are members of a novel class of sulfonamides that elevate endosomal and lysosomal pH, down-regulate cell surface receptors, and impair recycling of internalized transferrin receptors to the plasma membrane. In vitro experiments revealed that the sulfonamides directly inhibit adenosine triphosphate (ATP) hydrolysis by the V-ATPase and that they also possess a potent proton ionophore activity. While maintenance of organellar pH is known to be a critical factor in both endocytosis and exocytosis, the precise role of acidification, beyond the uncoupling of ligands from their receptors, remains largely unknown. Identification of this novel class of sulfonamide inhibitors provides new chemical tools to better understand the function of organelle pH in membrane traffic and the activity of V-ATPases in particular.

Optical studies of single molecules at room temperature

Recent developments in optical studies of single molecules at room temperature are reviewed, with an emphasis on the underlying principles and the potential of single-molecule experiments. Examples of single-molecule studies are given, including photophysics and photochemistry pertinent to single-molecule measurements, spectral fluctuations, Raman spectroscopy, diffusional motions, conformational dynamics, fluorescence resonant energy transfer, exciton dynamics, and enzymatic turnovers. These studies illustrate the information obtainable with the single-molecule approach that is hidden in ensemble-averaged measurements.

Salicylihalamide A inhibits the V0 sector of the V-ATPase through a mechanism distinct from bafilomycin A1

The newly identified specific V-ATPase inhibitor, salicylihalamide A, is distinct from any previously identified V-ATPase inhibitors in that it inhibits only mammalian V-ATPases, but not those from yeast or other fungi (Boyd, M. R., Farina, C., Belfiore, P., Gagliardi, S., Kim, J. W., Hayakawa, Y., Beutler, J. A., McKee, T. C., Bowman, B. J., and Bowman, E. J. (2001) J. Pharmacol. Exp. Ther. 297, 114-120). In addition, salicylihalamide A does not compete with concanamycin or bafilomycin for binding to V-ATPase, indicating that it has a different binding site from those classic V-ATPase inhibitors (Huss, M., Ingenhorst, G., Konig, S., Gassel, M., Drose, S., Zeeck, A., Altendorf, K., and Wieczorek, H. (2002) J. Biol. Chem. 277, 40544-40548). By using purified bovine brain V-pump and its dissociated V(1) and V(0) sectors, we identified the recognition and binding site for salicylihalamide to be within the V(0) domain. Salicylihalamide does not inhibit the ATP hydrolysis activity of the dissociated V(1)-ATPase but inhibits the ATPase activity of the holoenzyme by inhibiting the V(0) domain. Salicylihalamide causes a dramatic redistribution of cytosolic V(1) from soluble to membrane-associated form, a change not observed in cells treated with either bafilomycin or NH(4)Cl. By synthesizing and characterizing a series of salicylihalamide derivatives, we investigated the structural determinants of salicylihalamide inhibition in terms of potency and reversibility, and used this information to suggest a possible binding mechanism.

Flow and fracture in drying nanoparticle suspensions

Drying aqueous suspensions of monodisperse silica nanoparticles can fracture in remarkable patterns. As the material solidifies, evenly spaced cracks invade from the drying surface, with individual cracks undergoing intermittent motion. We show that the growth of cracks is limited by the advancement of the compaction front, which is governed by a balance of evaporation and flow of fluid at the drying surface. Surprisingly, the macroscopic dynamics of drying show signatures of molecular-scale fluid effects.

Characterization of the functional coupling of bovine brain vacuolar-type H(+)-translocating ATPase. Effect of divalent cations, phospholipids, and subunit H (SFD)

Vacuolar-type H+-translocating ATPases (V-ATPases or V-pumps) are complex proteins containing multiple subunits and are organized into two functional domains: a peripheral catalytic sector V1 and a membranous proton channel V0. The functional coupling of ATP hydrolysis activity to proton transport in V-pumps requires a regulatory component known as subunit H (SFD) as has been shown both in vivo and in vitro (Ho, M. N., Hirata, R., Umemoto, N., Ohya, Y., Takatsuki, A., Stevens, T. H., and Anraku, Y. (1993) J. Biol. Chem. 268, 18286-18292; Xie, X. S., Crider, B. P., Ma, Y. M., and Stone, D. K. (1994) J. Biol. Chem. 269, 25809-25815). Ca2+ is thought to uncouple V-pumps because it is found to support ATP hydrolysis but not proton transport, while Mg2+ supports both activities. The direct effect of phospholipids on the coupling of V-ATPases has not been reported, likely due to the fact that phospholipids are constituents of biological membranes. We now report that Ca2+-induced uncoupling of the bovine brain V-ATPase can be reversed by imposition of a favorable membrane potential. Furthermore we report a simple "membrane-free" assay system using the V0 proton channel-specific inhibitor bafilomycin as a probe to detect the coupling of V-ATPase under certain conditions. With this system, we have characterized the functional effect of subunit H, divalent cations, and phospholipids on bovine brain V-ATPase and have found that each of these three factors plays a critical role in the functional coupling of the V-pump.

High-sensitivity coherent anti-Stokes Raman scattering microscopy with two tightly synchronized picosecond lasers

We demonstrate a significant improvement in signal-to-noise ratio in coherent anti-Stokes Raman scattering (CARS) spectroscopy/microscopy, using two highly synchronized picosecond Ti:sapphire lasers. A temporal jitter between the pulse trains from the two independent commercial lasers is reduced from a few picoseconds to ~21 fs , maintained over several hours. The tight synchronization brings the fluctuation of the CARS signal down to the shot-noise limit, leading to enhanced CARS vibrational images of living cells and polymer beads.

Total synthesis and initial structure-function analysis of the potent V-ATPase inhibitors salicylihalamide A and related compounds

Salicylihalamide A is the first member of a growing class of macrocyclic salicylate natural products that induce a variety of interesting phenotypes in cultured mammalian cells. Salicylihalamide A was reported to be a unique and highly differential cytotoxin and a potent inhibitor of the mammalian vacuolar (H(+))-ATPase. The total synthesis of both enantiomers of salicylihalamide A, a revision of the absolute configuration assigned to the natural product, and extensive structure-function studies with synthetic salicylihalamide variants are reported. These studies were possible only due to a highly efficient synthetic strategy that features (1) a remarkably E-selective ring-closing olefin metathesis to construct the 12-membered benzolactone skeleton 29, (2) a mild stereocontrolled elaboration to E-alkenyl isocyanate 41, and (3) addition of carbon, oxygen, and sulfur nucleophiles to isocyanate 41 to obtain salicylihalamide A and congeners. We demonstrate for the first time that salicylihalamide A is a potent inhibitor of fully purified reconstituted V-ATPase from bovine brain, and have identified several similarly potent side chain modified derivatives, including salicylihalamide dimers 43-45. In combination, these studies have laid the foundation for ongoing studies aimed at a comprehensive understanding of salicylihalamide's mode-of-action, of potential relevance to the development of lead compounds for the treatment of osteoporosis and cancer.

Polarization coherent anti-Stokes Raman scattering microscopy

We report polarization coherent anti-Stokes Raman scattering (P-CARS) microscopy that allows vibrational imaging with high sensitivity and spectral selectivity. The nonresonant background signals from both Raman scatterers and the solvent are efficiently suppressed in P-CARS microscopy. We demonstrate P-CARS imaging of unstained cells based on the contrast of the protein amide I band.

Identification and functional expression of four isoforms of ATPase II, the putative aminophospholipid translocase. Effect of isoform variation on the ATPase activity and phospholipid specificity

ATPase II, a vanadate-sensitive and phosphatidylserine-dependent Mg(2+)-ATPase, is a member of a subfamily of P-type ATPase and is presumably responsible for aminophospholipid translocation activity in eukaryotic cells. The aminophospholipid translocation activity plays an important physiological role in the maintenance of membrane phospholipid asymmetry that is observed in the plasma membrane as well as the membranes of certain cellular organelles. While the preparations of ATPase II from different sources share common fundamental properties, such as substrate specificity, inhibitor spectrum, and phospholipid dependence, they are divergent in several characteristics. These include specific ATPase activity and phospholipid selectivity. We report here the identification of four isoforms of ATPase II in bovine brain. These isoforms are formed by a combination of two major variations in their primary sequences and show that the structural variation of these isoforms has functional significance in both ATPase activity and phosholipid selectivity. Furthermore, studies with the phosphoenzyme intermediate of ATPase II and its recombinant isoforms revealed that phosphatidylserine is essential for the dephosphorylation of the intermediate. Without phosphatidylserine, ATPase II would be accumulated as phosphoenzyme in the presence of ATP, resulting in the interruption of its catalytic cycle.

Single molecule physics and chemistry

New experiments using scanning probe microcopies and advanced optical methods allow us to study molecules as individuals, not just as populations. The findings of these studies not only include the confirmation of results expected from studies of bulk matter, but also give substantially new information concerning the complexity of biomolecules or molecules in a structured environment. The technique lays the groundwork for achieving the control of an individual molecule's motion. Ultimately, this work may lead to such practical applications as miniaturized sensors.

Recombinant SFD isoforms activate vacuolar proton pumps

The vacuolar proton pump of clathrin-coated vesicles is composed of two general sectors, a cytosolic, ATP hydrolytic domain (V1) and an intramembranous proton channel, V0. V1 is comprised of 8-9 subunits including polypeptides of 50 and 57 kDa, termed SFD (Sub Fifty-eight-kDa Doublet). Although SFD is essential to the activation of ATPase and proton pumping activities catalyzed by holoenzyme, its constituent polypeptides have not been separated to determine their respective roles in ATPase functions. Recent molecular characterization of these subunits revealed that they are isoforms that arise through an alternative splicing mechanism (Zhou, Z., Peng, S.-B., Crider, B.P., Slaughter, C., Xie, X.S., and Stone, D.K. (1998) J. Biol. Chem. 273, 5878-5884). To determine the functional characteristics of the 57-kDa (SFDalpha)1 and 50-kDa (SFDbeta) isoforms, we expressed these proteins in Escherichia coli. We determined that purified recombinant proteins, rSFDalpha and rSFDbeta, when reassembled with SFD-depleted holoenzyme, are functionally interchangeable in restoration of ATPase and proton pumping activities. In addition, we determined that the V-pump of chromaffin granules has only the SFDalpha isoform in its native state and that rSFDalpha and rSFDbeta are equally effective in restoring ATPase and proton pumping activities to SFD-depleted enzyme. Finally, we found that SFDalpha and SFDbeta structurally interact not only with V1, but also withV0, indicating that these activator subunits may play both structural and functional roles in coupling ATP hydrolysis to proton flow.

Identification and reconstitution of an isoform of the 116-kDa subunit of the vacuolar proton translocating ATPase

We have identified a cDNA encoding an isoform of the 116-kDa subunit of the bovine vacuolar proton translocating ATPase. The predicted protein sequence of the new isoform, designated a2, consists of 854 amino acids with a calculated molecular mass of 98,010 Da; it has approximately 50% identity to the original isoform (a1) we described (Peng, S.-B., Crider, B. P., Xie, X.-S., and Stone, D.K. (1994) J. Biol. Chem. 269, 17262-17266). Sequence comparison indicates that the a2 isoform is the bovine homologue of a 116-kDa polypeptide identified in mouse as an immune regulatory factor (Lee, C.-K., Ghoshal, K., and Beaman, K.D. (1990) Mol. Immunol. 27, 1137-1144). The bovine a1 and a2 isoforms share strikingly similar structures with hydrophilic amino-terminal halves that are composed of more than 30% charged residues and hydrophobic carboxyl-terminal halves that contain 6-8 transmembrane regions. Northern blot analysis demonstrates that isoform a2 is highly expressed in lung, kidney, and spleen. To determine the possible role of the a2 isoform in vacuolar proton pump function, we purified from bovine lung a vacuolar pump proton channel (VO) containing isoform a2. This VO conducts bafilomycin-sensitive proton flow after reconstitution and acid activation, and supports proton pumping activity after assembly with the catalytic sector (V1) of vacuolar-type proton translocating ATPase (V-ATPase) and sub-58-kDa doublet, a 50-57-kDa polypeptide heterodimer required for V-ATPase function. These data indicate that the a2 isoform of the 116-kDa polypeptide functions as part of the proton channel of V-ATPases.