Effect of water stress on the photosynthetic apparatus of plants and the protective role of cytokinins: A review

Characteristics of photosynthetic apparatus (the pool of pigments and proteins; the activity of photosystems; the intensities of in vivo photoassimilation of carbon dioxide and in vitro activity of enzymes of carbon metabolism; leaf structure; chloroplast structure), undergoing changes under the conditions of water deficiency, have been reviewed. The protective role of cytokinins is due to their regulatory effects on the renewal of disrupted cellular structures, the condition of the stomata, and de novo synthesis and activation of proteins that are required for increasing plant resistance to water stress.Translated from Prikladnaya Biokhimiya i Mikrobiologiya, Vol. 41, No. 2, 2005, pp. 133–147.Original Russian Text Copyright © 2005 by Chernyadev.     

Effects of Cytokinin Preparations on the Pools of Pigments and Proteins of Wheat Cultivars Differing in Their Tolerance to Water Stress

Contents of chlorophylls, carotenoids, soluble leaf proteins, and the key enzyme of carbon metabolism—ribulose bisphosphate carboxylase/oxygenase (RuBisCO; EC 4.1.1.39)—in young seedlings and adult leaves of the wheat Triticum aestivum L. cultivars Mironovskaya 808 and Lyutescens 758, contrasting in their water stress tolerances, were compared under conditions of normal available water supply, water deficiency, and subsequent rehydration. It was discovered that compounds displaying a cytokinin activity (6-benzylaminopurine, thidiazuron, kartolin-2, and kartolin-4) reduced the decreases in contents of chlorophylls, carotenoids, soluble leaf proteins, and RuBisCO, progressing with development of water stress, as well as contributed to their more rapid recovery. These compounds with cytokinin activity also accelerated restoration of the compounds studied to their initial concentrations during rehydration. The kartolin preparations caused a maximal protective effect. Water stress had a more pronounced negative effect on the cultivar Lyutescens 758. Dehydration resulted in a more extensive destruction of seedlings compared to leaves of adult plants.     

Effect of cytokinin preparations on the pools of pigments and proteins of wheat cultivars differing in their tolerance to water stress

Contents of chlorophylls, carotenoids, soluble leaf proteins, and the key enzyme of carbon metabolism--ribulose bisphosphate carboxylase/oxygenase (RuBisCO; EC 4.1.1.39)--in young seedlings and adult leaves of the wheat Triticum aestivum L. cultivars Mironovskaya 808 and Lyutestsens 758, contrasting in their water stress tolerances, were compared under conditions of normal available water supply, water deficiency, and subsequent rehydration. It was discovered that compounds displaying a cytokinin activity (6-benzylaminopurine, thidiazuron, cartolin-2, and cartolin-4) reduced the decreases in contents of chlorophylls, carotenoids, soluble leaf proteins, and RuBisCO progressing with development of water stress. These compounds with cytokinin activity also accelerated restoration of the compounds studied to their initial concentrations during rehydration. The cartolin preparations caused a maximal protective effect. Water stress had a more pronounced negative effect on cultivar Lyutestsens 758. Dehydration resulted in a more extensive destruction of seedlings compared to leaves of adult plants.     

Metaproteomic analysis of a winter to spring succession in coastal northwest Atlantic Ocean microbial plankton

In this study, we used comparative metaproteomics to investigate the metabolic activity of microbial plankton inhabiting a seasonally hypoxic basin in the Northwest Atlantic Ocean (Bedford Basin). From winter to spring, we observed a seasonal increase in high-affinity membrane transport proteins involved in scavenging of organic substrates; Rhodobacterales transporters were strongly associated with the spring phytoplankton bloom, whereas SAR11 transporters were abundant in the underlying waters. A diverse array of transporters for organic compounds were similar to the SAR324 clade, revealing an active heterotrophic lifestyle in coastal waters. Proteins involved in methanol oxidation (from the OM43 clade) and carbon monoxide (from a wide variety of bacteria) were identified throughout Bedford Basin. Metabolic niche partitioning between the SUP05 and ARCTIC96BD-19 clades, which together comprise the Gamma-proteobacterial sulfur oxidizers group was apparent. ARCTIC96BD-19 proteins involved in the transport of organic compounds indicated that in productive coastal waters this lineage tends toward a heterotrophic metabolism. In contrast, the identification of sulfur oxidation proteins from SUP05 indicated the use of reduced sulfur as an energy source in hypoxic bottom water. We identified an abundance of Marine Group I Thaumarchaeota proteins in the hypoxic deep layer, including proteins for nitrification and carbon fixation. No transporters for organic compounds were detected among the thaumarchaeal proteins, suggesting a reliance on autotrophic carbon assimilation. In summary, our analyses revealed the spatiotemporal structure of numerous metabolic activities in the coastal ocean that are central to carbon, nitrogen and sulfur cycling in the sea.     

Impact of macromolecular crowding on the mesomorphic behavior of lipid self-assemblies

Using LAURDAN fluorescence we observed that water dynamics measured at the interface of DOPC bilayers can be differentially regulated by the presence of crowded suspensions of different proteins (HSA, IgG, Gelatin) and PEG, under conditions where the polymers are not in direct molecular contact with the lipid interface. Specifically, we found that the decrease in water dipolar relaxation at the membrane interface correlates with an increased fraction of randomly oriented (or random coil) configurations in the polymers, as Gelatin > PEG > IgG > HSA. By using the same experimental strategy, we also demonstrated that structural transitions from globular to extended conformations in proteins can induce transitions between lamellar and non-lamellar phases in mixtures of DOPC and monoolein. Independent experiments using Raman spectroscopy showed that aqueous suspensions of polymers exhibiting high proportions of randomly oriented conformations display increased fractions of tetracoordinated water, a configuration that is dominant in ice. This indicates a greater capacity of this type of structure for polarizing water and consequently reducing its chemical activity. This effect is in line with one of the tenets of the Association Induction Hypothesis, which predicts a long-range dynamic structuring of water molecules via their interactions with proteins (or other polymers) showing extended conformations. Overall, our results suggest a crucial role of water in promoting couplings between structural changes in macromolecules and supramolecular arrangements of lipids. This mechanism may be of relevance to cell structure/function when the crowded nature of the intracellular milieu is considered.     

Proteome analysis of leaves of the desiccation-tolerant grass, Sporobolus stapfianus, in response to dehydration

Drought and its affects on agricultural production is a serious issue facing global efforts to increase food supplies and ensure food security for the growing world population. Understanding how plants respond to dehydration is an important prerequisite for developing strategies for crop improvement in drought tolerance. This has proved to be a difficult task as all of the current research plant models do not tolerate cellular dehydration well and, like all crops, they succumb to the effects of a relatively small water deficit of −4 MPa or less. For these reasons many researchers have started to investigate the usefulness of resurrection plants, plants that can survive extremes of dehydration to the point of desiccation, to provide answers as to how plants tolerate water loss. We have chosen to investigate the leaf proteome response of the desiccation-tolerant grass Sporobolus stapfianus Gandoger to dehydration to a water content that encompasses the initiation of the cellular protection response evident in these plants. We used a combination of two-dimensional Difference Gel Electrophoresis (2D-DIGE) and liquid chromatography-tandem-mass spectrometry to compare the proteomes of young leaves from hydrated plants to those dehydrated to approximately 30% relative water content. High-resolution 2D-DIGE revealed 96 significantly different proteins and 82 of these spots yielded high-quality protein assignments by tandem-mass spectrometry. Inferences from the bioinformatic annotations of these proteins revealed the possible involvement of protein kinase-based signaling cascades and brassinosteroid involvement in the regulation of the cellular protection response. Enzymes of glycolysis, both cytoplasmic and plastidic, as well as five enzymes of the Calvin cycle increased in abundance. However, the RuBisCO large subunit and associated proteins were reduced, indicating a loss of carbon fixation but a continued need to supply the necessary carbon skeletons for the constituents involved in cell protection. Changes in abundance of several proteins that appear to have a function in chromatin structure and function indicate that these structures undergo significant changes as a result of dehydration. These observations give a unique “snap-shot” of the proteome of S. stapfianus at a critical point in the passage towards desiccation.     

青海湖岸带土壤与沉积物的地化特征与细菌群落对水位上升的响应

【目的】探究青海湖岸带土壤与沉积物的地化特征与细菌群落对水位扩张的响应。【方法】从岸上至岸下沿垂直青海湖岸带方向,采集距离湖面不同高度土壤(土壤：S1、S2)、岸边不同水深表层沉积物(过渡区：E0、E6、E17)及湖心表层沉积物(沉积物：D1、D2)样品,土壤与沉积物水深(土壤水深表示为负数)从小到大的变化表征岸边土壤被淹水转变为沉积物的过程。采用地球化学分析和16SrRNA基因高通量测序技术,探究岸带土壤与沉积物样品中的地化特征与微生物群落构成。【结果】青海湖水位上升导致的生境转变对岸带土壤与沉积物的理化性质、营养水平、有机碳类型等地化特征产生显著影响。具体表现为,随着水位升高,岸带土壤与沉积物的pH、矿物结合态有机碳含量显著升高,而碳氮比值、可溶性有机碳(dissolved organic carbon,DOC)、颗粒态有机碳含量显著下降。随着水位上升,青海湖岸带被淹没土壤的细菌群落多样性下降,且群落结构发生明显变化。这种变化与环境因子变化密切相关,具体表现为,细菌群落物种丰富度指数和香农多样性指数随着水位上升呈下降趋势;活性金属结合态有机碳含量与细菌群落多样性的变化密切相关;理化...     

CARd-3D: Carbon Distribution in 3D Structure Program for Globular Proteins

Spatial arrangement of carbon in protein structure is analyzed here. Particularly, the carbon fractions around individual atoms are compared. It is hoped that it follows the principle of 31.45% carbon around individual atoms. The results reveal that globular protein''s atoms follow this principle. A comparative study on monomer versus dimer reveal that carbon is better distributed in dimeric form than in its monomeric form. Similar study on solid versus liquid structures reveals that the liquid (NMR) structure has better carbon distribution over the corresponding solid (X-Ray) structure. The carbon fraction distributions in fiber and toxin protein are compared. Fiber proteins follow the principle of carbon fraction distribution. At the same time it has another broad spectrum of carbon distribution than in globular proteins. The toxin protein follows an abnormal carbon fraction distribution. The carbon fraction distribution plays an important role in deciding the structure and shape of proteins. It is hoped to help in understanding the protein folding and function.     

Proteomics Analysis of Soybean Seedlings under Short-Term Water Deficit

Soybeans are one of the most important grain crops worldwide. Water deficit, which seriously affects the yield and quality of soybeans, is the main abiotic stress factor in soybean production. As a follow-up study, the droughttolerant soybean variant Heinong 44 was analyzed via proteome analysis. Soybean was exposed to water deficit for 0, 8, and 24 h, and protein samples were extracted for detection of differentially expressed proteins. Protein sequencing of leaf tissues under water stress yielded a total of 549 differentially expressed proteins: 75 and 320 upregulated proteins as well as 70 and 84 downregulated proteins were obtained after 8 and 24 h of water deficit, respectively. Gene Ontology analysis revealed that most of the differentially expressed proteins (DEPs) were involved in catalytic activity, molecular function, and metabolic processes, whereas some of them were involved in photosynthesis, carbon metabolism, and energy metabolism. We also identified some differentially expressed proteins that may be involved in the regulation of water deficit response. Our study provides a theoretical basis for the breeding of drought-resistant soybean varieties.     

青藏高原泥炭地水位下降促进土壤碳积累的影响机制

酚类物质作为泥炭地重要的碳分解抑制剂,植被作为泥炭地关键的碳输入来源,它们在土壤碳(可溶性有机碳(DOC)等)周转过程中都发挥着重要作用。然而,目前关于植被群落结构、酚类物质以及DOC含量对水位波动的响应存在较大争议。因此,为明确泥炭地水位下降对植被群落结构、酚类物质以及DOC含量的影响并探明三者间的潜在联系,以若尔盖高原泥炭地作为研究对象,选取红原县日干乔地区3处不同地下水位泥炭地(水位由高到低依次为S1(-1.9 cm)、S2(-10 cm)、S3(-19 cm)样地),调查不同水位条件下植被群落结构特征,并探究酚类物质及土壤碳含量对水位波动的响应。结果表明:(1)从S1到S3样地水位下降促进土壤DOC显著增加(P<0.05),土壤总碳从S1到S2显著增加(P<0.05),而从S2到S3无显著差异;(2)泥炭地水位下降促使禾本科(发草Deschampsia cespitosa)、莎草科(木里薹草Carex muliensis、乌拉草Carex meyeriana)植物大量出现,植被群落高度显著增加(P<0.05)。植被群落地上生物量由153.67 g/m~2增加至...     

Molecular basis for the special properties of proteins and enzymes from Halobacterium marismortui

Abstract Three proteins from Halobacterium marismortui , malate dehydrogenase (hMDH), glutamate dehydrogenase (hGDH) and ferredoxin (hFD) were purified and characterized with respect to their molecular masses, amino acid composition and, for hFD only, primary structure. Striking features of halophilic proteins are: the high excess of acidic over basic residues; acidic clusters in the sequence. Low-salt concentration causes inactivation and changes in structural parameters of hMDH and hGDH. Reactivation of hMDH involves long-lived stable intermediates. The salt concentration optimum of enzymic activity is independent of salt nature. The high capacity of halophilic proteins to retain water and salt is due to unique molecular properties, studied by physico-chemical techniques.     

Effects of Cytokinin Preparations on the Stability of the Photosynthetic Apparatus of Two Wheat Cultivars Experiencing Water Deficiency

Carboxylase activity of the key enzyme of carbon metabolism, ribulose-bisphosphate carboxylase/oxygenase (RuBisCO; EC 4.1.1.39), and phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31), as well as the intensity of carbon dioxide photosynthetic assimilation in young seedlings and adult leaves of the wheat Triticum aestivum L. cultivars Mironovskaya 808 (a more tolerant) and Lyutestsens758 (a less tolerant), were compared under conditions of progressive water deficiency. The water stress had more pronounced negative effects on all the studied characteristics of the photosynthetic apparatus of the cultivar Lyutestsens758. Its seedlings were more sensitive to water stress. Compounds with a cytokinin activity (6-benzylaminopurine, thidiazuron, kartolin 2, and kartolin 4) played a protective role, increasing the stability of the photosynthetic apparatus under conditions of water deficiency. Preparations of kartolins displayed the maximum protective effect.     

Group III alcohol dehydrogenase from Pectobacterium atrosepticum: insights into enzymatic activity and organization of the metal ion-containing region

NAD(P)⁺-dependent alcohol dehydrogenases (ADH) are widely distributed in all phyla. These proteins can be assigned to three nonhomologous groups of isozymes, with group III being highly diverse with regards to catalytic activity and primary structure. Members of group III ADHs share a conserved stretch of amino acid residues important for cofactor binding and metal ion coordination, while sequence identities for complete proteins are highly diverse (<20 to >90 %). A putative group III ADH PaYqhD has been identified in BLAST analysis from the plant pathogenic enterobacterium Pectobacterium atrosepticum. The PaYqhD gene was expressed in the heterologous host Escherichia coli, and the recombinant protein was purified in a two-step purification procedure to homogeneity indicating an obligate dimerization of monomers. Four conserved amino acid residues involved in metal ion coordination were substituted with alanine, and their importance for catalytic activity was confirmed by circular dichroism spectrum determination, in vitro, and growth experiments. PaYqhD exhibits optimal activity at 40 °C with short carbon chain aldehyde compounds and NADPH as cofactor indicating the enzyme to be an aldehyde reductase. No oxidative activities towards alcoholic compounds were detectable. EDTA completely inhibited catalytic activity and was fully restored by the addition of Co²⁺. Activity measurements together with sequence alignments and structure analysis confirmed that PaYqhD belongs to the butanol dehydrogenase-like enzymes within group III of ADHs.     

Enzyme activity evaluation of organic solvent-treated phenylalanine ammonia lyase

The direct one-step synthesis of L-phenylalanine methyl ester in an organic-aqueous biphasic system using phenylalanine ammonia lyase (E.C.4.3.1.5, PAL) containing Rhodotorula glutinis yeast whole cells was reported earlier. We report here further optimization of this biotransformation using isolated PAL, when the lyophilized enzyme is treated with different water miscible and water immiscible organic solvents. Use of isolated PAL enzyme is advantageous in overcoming diffusion barriers encountered when using PAL containing R.glutinis whole cells, and resulted in increased product yield due to better interaction of enzyme with the substrate. Among the water miscible solvents, ethanol treated and methanol-treated enzymes supported maximum PAL forward and reverse activities; respectively. In the water immiscible solvents category, heptane-treated enzyme exhibited maximal activity for both PAL forward and reverse reactions. PAL activity obtained with enzyme specimens treated with methanol, ethanol, and heptane varied in the range of 91–99% of that observed in aqueous buffer medium for the forward reaction; and 89–95% for the reverse reaction. n-butanol,acetone, and benzene were found to have a inhibitory effect on PAL enzyme, in that, it resulted in only 31–33% activity of that obtained with aqueous solution. Raman spectroscopy was used to monitor amide I and II bands which are sensitive to changes in the secondary structure of proteins. No changes in structure could be detected from the analyses of AI and AII bands of PAL spectra. This data obtained for PAL, a tetramer, could be significant in predicting how solvent interactions affect the structure and function of multimeric proteins and enzymes in nonaqueous media.     

胶州湾滨海湿地凋落物分解对土壤有机碳矿化的影响

通过室内培养试验和三维荧光光谱技术(3D-EEMs),开展了胶州湾滨海湿地碱蓬、芦苇和互花米草的分解对土壤有机碳矿化的影响研究。结果表明,凋落物的添加提高了土壤有机碳矿化速率和累积矿化量,具体表现为碱蓬互花米草芦苇空白对照;乘幂曲线模型能较好地描述有机碳矿化速率和累积矿化量的变化趋势。光谱分析表明,分解过程中类蛋白荧光强度始终大于类腐殖酸荧光强度;利用荧光区域积分进行定量分析表明,不同处理下类蛋白质物质占比最高,类腐殖质物质次之;荧光参数表明,土壤有机碳的芳香化程度在培养期间先升高后降低。凋落物分解通过增加土壤中的营养物质,提高了土壤中微生物活性,从而改变了土壤有机碳的结构和化学组分,且凋落物的植被特征决定了其对土壤有机碳矿化影响程度的大小。     

A crystallographic study of the complex of phosphoramidon with thermolysin. A model for the presumed catalytic transition state and for the binding of extended substrates

The structure of the thermolysin inhibitor phosphoramidon (N-(α-l-rhamnopyranosyl-oxyhydroxyphosphinyl)-l-leucyl-l-tryptophan bound to the crystalline enzyme has been determined to a resolution of 2.3 Å by X-ray crystallography. The study shows that the complex of phosphoramidon with thermolysin resembles that of the presumed catalytic transition state inferred from the geometry of binding of dipeptide inhibitors. Also, the study reveals the mode of binding of thermolysin substrates extended on the imino side of the scissile peptide bond.The crystallographic results are consistent with a variety of other studies on the catalytic activity of thermolysin, and suggest a mechanism of action which is analogous to one of the two alternative mechanisms proposed by Lipscomb and co-workers (1968) for carboxypeptidase A. Key features of the proposed mechanism are that the substrate is initially bound to the enzyme with the carbonyl oxygen of the scissile peptide liganded to the zinc; that Glu143 promotes the nucleophilic attack of a buried water molecule on the carbonyl carbon, forming a tetrahedral intermediate; and that His231 acts as a proton donor. The observed binding of phosphoramidon to thermolysin provides further evidence supporting the mechanism in which Glu143 acts as a general base, promoting the attack of water on the carbonyl carbon, rather than the alternative mechanism in which Glu143 attacks the carbonyl carbon directly, forming an anhydride intermediate.     

黄土高原土壤水分-有机碳-微生物耦合作用研究进展

黄土高原植被恢复后土壤水分、有机碳和微生物群落发生了非同步性演变。土壤微生物是各种生命活动的载体,在土壤水-碳耦合过程中参与了一系列的氧化与还原反应,因此,土壤微生物在水-碳耦合关键过程中起着重要的调节作用,三者存在着密切的耦合关系。尽管关于植被恢复后土壤水分和有机碳变化的研究已开展较多,但是由于土壤微生物活动和群落结构复杂性和易变性,这给土壤微生物介导的水-碳耦合研究带来了相当大的困难。迄今为止,黄土高原植被恢复后土壤水、碳、微生物三者之间的耦合关系缺乏总体性的融合,大多数研究只能假设各个生物化学过程是相对独立的,对土壤水、碳、微生物耦合的认知仍存在局限性。由此,首先对黄土高原植被恢复进程、土壤水分过程和有机碳变化分别进行了综述,结合已有的理论和证据进一步概括了黄土高原土壤有机碳、微生物群落对降水格局的响应。最后整合植被、土壤和微生物界面等关键生态过程,总结了黄土高原土壤水-碳-微生物耦合界面过程,采用HYDRUS-2D模型(水文过程模型)和ORCHIDEE模型(生态系统碳模型),并融入土壤微生物种群生长动态,基于稳定碳、水同位素技术和DNA探针技术,初步构建了黄土高原土壤水-碳-微...     

Influence of chemical chaperones on the properties of lysozyme and the reaction center protein from <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis>

The influence of three chemical chaperones: glycerol, 4-hexylresorcinol, and 5-methylresorcinol on the structure, equilibrium fluctuations, and functional activity of the hydrophilic enzyme lysozyme and the transmembrane reaction center (RC) protein from Rb. sphaeroides in a broad range of concentrations has been studied. The chosen chemical chaperones differ strongly in their structure and action on hydrophilic and membrane proteins. The influence of the chemical chaperones (except methylresorcinol) on the structure, dynamics, and functional properties of lysozyme and RC protein are well described in the framework of extended models of preferential hydration and preferential interaction of protein with a chemical chaperone. A molecule of hexylresorcinol consists of a hydrophobic (alkyl radical) and a hydrophilic (aromatic core) moieties; this provides for additional regulation of the functional activity of lysozyme and RC by hexylresorcinol. The influence of methylresorcinol on proteins differs from that of glycerol and hexylresorcinol. Methylresorcinol interacts with the surface of lysozyme directly, not via water hydrogen bonds. This leads to a decrease in the denaturation temperature and an increase in the amplitude of equilibrium fluctuations, allowing it to be a powerful activator. Methylresorcinol interacts with the membrane RC protein only by the condensation of hydration water, which is negligible in this case. Therefore, methylresorcinol does not affect the functional properties of the RC protein. It is concluded that different chaperones at the same concentration as well as one and the same chaperone at different concentrations produce protein 3D structures differing in dynamic and functional characteristics.     

Loss of the Photosynthetic Capacity and Proteins in Senescing Leaves at Top Positions of Two Cultivars of Rice in Relation to the Source Capacities of the Leaves for Carbon and Nitrogen

Senescing leaves are a source organ of both carbon and nitrogenbut, because degradation of chloroplast proteins and exportof their degradation products to sink organs give rise to lossof the photosynthetic capacity, the leaves serve as the sourceof nitrogen only at the cost of their source capacity for carbon.Changes in the photosynthetic capacity and levels of proteinsin leaves at the top four positions of two cultivars of rice,Nipponbare and Akenohoshi, during the ripening stage were investigatedtaking the trade-off relationship between the two source capacitiesinto consideration. Rate of light-saturated photosynthesis (Pmax)in leaves decreased more rapidly in Nipponbare than in Akenohoshiafter heading. Various proteins were also degraded during senescence,with Nipponbare leaves showing faster loss of proteins thanthe corresponding leaves of Akenohoshi. Decline in Pmax wascorrelated, similarly in the two cultivars, with losses of ribulose-l,5-bisphosphatecarboxylase/oxygenase, soluble proteins, chlorophyll a thatbound to the reaction center complexes of the two photosystems,the activity of whole-chain electron transport, and a majorpart of insoluble proteins during senescence. The results suggestthat degradation of proteins during senescence of rice leavesis coordinated so as to enable the leaves to perform photosynthesiswith a high use efficiency of protein and export nitrogen ata low or nearly minimum cost of the source capacity for carbon. ⁵ Present address: Section of Biology, University of California,Davis, California 95616, U.S.A. ⁶ Present address: Faculty of Agriculture, Utsunomiya University,350 Mine-machi, Utsunomiya, 321 Japan.     

Rampant Exchange of the Structure and Function of Extramembrane Domains between Membrane and Water Soluble Proteins

Of the membrane proteins of known structure, we found that a remarkable 67% of the water soluble domains are structurally similar to water soluble proteins of known structure. Moreover, 41% of known water soluble protein structures share a domain with an already known membrane protein structure. We also found that functional residues are frequently conserved between extramembrane domains of membrane and soluble proteins that share structural similarity. These results suggest membrane and soluble proteins readily exchange domains and their attendant functionalities. The exchanges between membrane and soluble proteins are particularly frequent in eukaryotes, indicating that this is an important mechanism for increasing functional complexity. The high level of structural overlap between the two classes of proteins provides an opportunity to employ the extensive information on soluble proteins to illuminate membrane protein structure and function, for which much less is known. To this end, we employed structure guided sequence alignment to elucidate the functions of membrane proteins in the human genome. Our results bridge the gap of fold space between membrane and water soluble proteins and provide a resource for the prediction of membrane protein function. A database of predicted structural and functional relationships for proteins in the human genome is provided at sbi.postech.ac.kr/emdmp.