PubMed Health⌕ Search

Biomedical subjects

Lei Li

Publications and source records attributed to Lei Li.

At least 55 records · Page 3Linked to original sources
PubMed2006

Series of new cationic iridium(III) complexes with tunable emission wavelength and excited state properties: structures, theoretical calculations, and photophysical and electrochemical properties.

A series of new cationic iridium(III) complexes [Ir(piq)2(N/\N)]+PF6- (1-6) (piq =1-phenyl-isoquinoline) containing N/\N ligands with different conjugated lengths were synthesized, where the six N/\N ligands were bipyridine, phenanthroline, 2-pyridyl-quinoline, 2,2'-biquinoline, 1,1'-biisoquinoline, and 2-(2-quniolinyl)quinoxaline. Single-crystal X-ray diffraction spectra of three complexes were studied, and the iridium(III) centers were found to adopt a distorted octahedral coordination geometry with cis metalated carbons and trans nitrogen atoms. UV-vis, photoluminescence, cyclic voltammetry, and theoretical calculations were employed for studying the photophysical and electrochemical properties. And the excited-state properties were investigated in detail. The excited state of complexes is complicated and contains triplet metal-to-ligand charge transfer (3MLCT), triplet ligand-to-ligand charge transfer (3LLCT), and ligand-centered (cyclometalated) (3LC) transitions simultaneously. Importantly, the emission wavelength can be tuned significantly from 586 to 732 nm by changing the conjugated length of N/\N ligands.

Journal Article↗
PubMed2006

Rad17 phosphorylation is required for claspin recruitment and Chk1 activation in response to replication stress.

The ATR-mediated checkpoint is not only critical for responding to genotoxic stress but also essential for cell proliferation. The RFC-related checkpoint protein Rad17, a phosphorylation substrate of ATR, is critical for ATR-mediated checkpoint signaling and cell survival. Here, we show that phosphorylation of Rad17 by ATR is important for genomic stability and restraint of S phase but is not essential for cell survival. The phosphomutant Rad17AA exhibits distinct defects in hydroxyurea- (HU) and ultraviolet- (UV) induced Chk1 activation, indicating that separate Rad17 functions are required differently in response to different types of replication interference. Although cells expressing Rad17AA can initiate Chk1 phosphorylation after HU treatment, they fail to sustain Chk1 phosphorylation after withdrawal of HU and are profoundly sensitive to HU. Importantly, we found that phosphorylated Rad17 interacts with Claspin and regulates its phosphorylation. These findings reveal a phosphorylation-dependent function of Rad17 in an ATR-Rad17-Claspin-Chk1-signaling cascade that responds to specific replication stress.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Synthesis and antitumor activity of novel 10-substituted camptothecin analogues.

In an attempt to improve the antitumor activity and decrease the cytotoxicity of camptothecin, 18 new 10-substituted camptothecin derivatives were prepared. The cytotoxicity in vitro on cancer cell lines and antitumor activity in vivo, and inhibitory properties of topoisomerase I of these derivatives were evaluated. Most of these derivatives possessed lower cytotoxicities than CPT, and the compounds 13, 21, 22, 23, and 24 showed similar topoisomerase I inhibitory activity to CPT. Analogues 13 exhibited the best antitumor activity in vivo among all derivatives we prepared.

Animals↗
PubMed2006

Importance in catalysis of the 6-phosphate-binding site of 6-phosphogluconate in sheep liver 6-phosphogluconate dehydrogenase.

The 6-phosphate of 6-phosphogluconate (6PG) is proposed to anchor the sugar phosphate in the active site and aid in orientating the substrate for catalysis. In order to test this hypothesis, alanine mutagenesis was used to probe the contribution of residues in the vicinity of the 6-phosphate to binding of 6PG and catalysis. The crystal structure of sheep liver 6-phosphogluconate dehydrogenase shows that Tyr-191, Lys-260, Thr-262, Arg-287, and Arg-446 contribute a mixture of ionic and hydrogen bonding interactions to the 6-phosphate, and these interactions are likely to provide the majority of the binding energy for 6PG. All mutant enzymes, with the exception of T262A, exhibit an increase in K(6PG) that ranges from 5- to 800-fold. There is also a less pronounced increase in K(NADP), ranging from 3- to 15-fold, with the exception of T262A. The R287A and R446A mutant enzymes exhibit a dramatic decrease in V/E(t) (600- and 300-fold, respectively) as well as in V/K(6PG)E(t) (10(5) - and 10(4)-fold), and therefore no further characterization was carried out with these two mutant enzymes. No change in V/E(t) was observed for the Y191A mutant enzyme, whereas 20- and 3-fold decreases were obtained for the K260A and T262A mutant enzymes, respectively, resulting in a decrease in V/K(6PG)E(t) range from 3- to 120-fold. All mutant enzymes also exhibit at least an order of magnitude increase in 13C-isotope effect -1, indicating that the decarboxylation step has become more rate-limiting. Data are consistent with significant roles for Tyr-191, Lys-260, Thr-262, Arg-287, and Arg-446 in providing the binding energy for 6PG. In addition, these residues also likely ensure proper orientation of 6PG for catalysis and aid in inducing the conformation change that precedes, and sets up the active site for, catalysis.

Amino Acid Sequence↗
PubMed2006

Antioxidant constituents in the fruits of Luffa cylindrica (L.) Roem.

Hydrophilic antioxidant constituents in the fruits of the vegetable Luffa cylindrica (L.) Roem (sponge gourds) were separated by an antioxidant-guided assay to yield eight compounds: p-coumaric acid (1), 1-O-feruloyl-beta-D-glucose (2), 1-O-p-coumaroyl-beta-D-glucose (3), 1-O-caffeoyl-beta-D-glucose (4), 1-O-(4-hydroxybenzoyl)glucose (5), diosmetin-7-O-beta-D-glucuronide methyl ester (6), apigenin-7-O-beta-D-glucuronide methyl ester (7), and luteolin-7-O-beta-D-glucuronide methyl ester (8). The eight compounds were isolated by high-speed countercurrent chromatography and identified by electrospray ionization-mass spectrometry and NMR analysis, and the antioxidant activity was evaluated by the radical scavenging effect on the 1,1-diphenyl-2-picrylhydrazyl radical. High-performance liquid chromatography analysis showed that a total amount of the eight compounds in the dried gourds without skin was about 1%. The results demonstrate that the consumption of sponge gourds can supply some antioxidant constituents to human body.

Antioxidants↗
PubMed2006

Using classification trees to assess low birth weight outcomes.

OBJECTIVE: Low birth weight (LBW) is a major public health problem. Compared to normal weight infants, LBW is positively associated with infant mortality and negatively associated with normative childhood cognitive and physical development. In the past two decades, research has identified important risk factors of LBW. In this study, we used classification trees to study the interactive nature of these factors. In particular we: (1) identify subgroups of women who are at a high risk of a LBW outcome in seven geographical regions of Florida, and (2) study the predictive performance of classification trees by comparing the tree-based results to those obtained using logistic regression. METHODS: The data, 181,690 singleton births, were derived from Florida birth certificates recorded in 1998. Classification trees and logistic regression models were built based on seven geographical regions. The outcome variable consisted of two classes, namely LBW (< 2500 g) and normal birth weight (> or = 2500 g) cases, while a large number of known risk factors was examined. Tree and logistic regression models were compared using Receiving Operating Curves, and sensitivity and specificity analyses. RESULTS: The use of classification trees has revealed a number of high-risk subgroups. For instance, White, Hispanic or Other non-white mothers who were healthy and smoked with a weight gain less than 20 lbs had a higher risk of a LBW birth compared to those with the same characteristics but with a weight gain of more than 20 lbs. Factors such as parity and marital status were important predictors for pregnancy outcomes among nonsmoker White, Hispanic or Other non-white mothers. Furthermore, we found that Black mothers were directly classified as a high-risk subgroup in the regions of Panhandle, Northeast, North Central, while in the Southern regions a series of other characteristics further defined the high-risk subgroup of Black mothers. Overall, the differences in predictive performance between tree models and logistic regression were minimal. CONCLUSION: The present study demonstrated that classification trees can be used to identify high-risk subgroups of mothers who are at risk of LBW outcomes. Although these exploratory tree analyses revealed a number of distinctive variable interactions for each geographical area, the variable selection was similar across all seven regions. This study also demonstrated that classification trees did not outperform logistic regression models or vice versa; both approaches provided useful analyses of the data.

Adolescent↗
PubMed2006

Ischemic insults direct glutamate receptor subunit 2-lacking AMPA receptors to synaptic sites.

Regulated AMPA receptor (AMPAR) trafficking at excitatory synapses is a mechanism critical to activity-dependent alterations in synaptic efficacy. The role of regulated AMPAR trafficking in insult-induced synaptic remodeling and/or cell death is, however, as yet unclear. Here we show that brief oxygen-glucose deprivation (OGD), an in vitro model of brain ischemia, promotes redistribution of AMPARs at synapses of hippocampal neurons, leading to a switch in AMPAR subunit composition. Ischemic insults promote internalization of glutamate receptor subunit 2 (GluR2)-containing AMPARs from synaptic sites via clathrin-dependent endocytosis and facilitate delivery of GluR2-lacking AMPARs to synaptic sites via soluble N-ethylmaleimide-sensitive factor attachment protein receptor-dependent exocytosis, evident at early times after insult. The OGD-induced switch in receptor subunit composition requires PKC activation, dissociation of GluR2 from AMPA receptor-binding protein, and association with protein interacting with C kinase-1. We further show that AMPARs at synapses of insulted neurons exhibit functional properties of GluR2-lacking AMPARs. AMPAR-mediated miniature EPSCs exhibit increased amplitudes and enhanced sensitivity to subunit-specific blockers of GluR2-lacking AMPARs, evident at 24 h after ischemia. The OGD-induced alterations in synaptic AMPA currents require clathrin-mediated receptor endocytosis and PKC activation. Thus, ischemic insults promote targeting of GluR2-lacking AMPARs to synapses of hippocampal neurons, mechanisms that may be relevant to ischemia-induced synaptic remodeling and/or neuronal death.

Animals↗
PubMed2006

Hypoxia-inducible factor-1alpha induces the epithelial-mesenchymal transition of human prostatecancer cells.

BACKGROUND: Hypoxia-inducible factor-1alpha (HIF-1alpha) is a transcriptional factor that could improve the stimulation of angiogenesis and the metabolic adaptation of tumor cells to hypoxia. A recent study showed that HIF-1alpha could induce colon cancer cells epithelial-mesenchymal transition (EMT). However, no evidence indicates a similar correlation in human prostate cancer cells. This study was designed to evaluate the effect of HIF-1alpha over-expression on the EMT in human prostate cancer cells. METHODS: We selected the appropriate cell line for HIF-1alpha induction from those EMT negative prostate cell lines through vimentin gene detection by RT-PCR. As the result, LNCaP cell line is the best one for further experiment. LNCaP cells were transfected with recombinant plasmid pcDNA3.1 (-)/HIF-1alpha and pcDNA3.1 (-) control vector by Lipofectamine 2000 system. The positive cell colonies were confirmed by indirect immunofluorescence labeling. Then Transwell polycarbonate filter was used to analyze the invasive potency. The expression of EMT associated proteins, E-cadherin and vimentin, was detected by Western blotting. RESULTS: Among four of the EMT negative cell lines, LNCaP was the only one expressed the vimentin gene but not the associated protein. The expression level of HIF-1alpha in LNCaP/HIF-1alpha was distinctly higher than that in LNCaP/pcDNA3.1 and LNCaP. The cell numbers of LNCaP/HIF-1alpha that penetrated through the Transwell filter were higher than that of LNCaP/pcDNA3.1 and LNCaP. Compared with the LNCaP/pcDNA3.1 and LNCaP cells, the expression of vimentin was up-regulated in LNCaP/HIF-1alpha, whereas the expression of E-cadherin was down-regulated. CONCLUSIONS: Over-expression of HIF-1alpha stimulates the invasion potency of human prostate carcinoma cells through EMT pathway. The expression of E-cadherin and vimentin, playing established roles in EMT, could be regulated by HIF-1alpha in human prostate cancer cell line.

Cadherins↗
PubMed2006

Repair of DNA interstrand cross-links: interactions between homology-dependent and homology-independent pathways.

DNA interstrand cross-links (ICLs) are complex DNA lesions generated by bifunctional alkylating agents, a class of compounds extensively used in cancer chemotherapy. Formation of an ICL covalently links the opposing strands of the double helix and results in severe disruptions of normal DNA functions, such as replication, transcription, and recombination. Because of the structural complexity, ICLs are most likely recognized by a variety of repair recognition proteins and processed through multiple mechanisms. To study the involvement of different repair pathways in ICL processing, we examined a variety of mammalian mutants with distinct DNA repair deficiencies. We found that the presence of ICLs induces frequent recombination between direct repeat sequences, suggesting that the single-strand annealing pathway may be an important mechanism for the removal of ICLs situated within direct repeats. Unlike recombination-independent ICL repair, ICL-induced single-strand annealing does not require the nucleotide excision repair (NER) mechanism. In cells defective in the mismatch repair protein Msh2, the level of recombination-independent ICL repair was significantly increased, suggesting that processing by the mismatch repair mechanism may lead to recombinational repair of ICLs. Our results suggest that removal of ICLs may involve two error-prone mechanisms depending on the sequence context of the cross-linked site.

Animals↗
PubMed2006

REV3 and REV1 play major roles in recombination-independent repair of DNA interstrand cross-links mediated by monoubiquitinated proliferating cell nuclear antigen (PCNA).

DNA interstrand cross-links (ICLs) are the most cytotoxic lesions to eukaryotic genome and are repaired by both homologous recombination-dependent and -independent mechanisms. To better understand the role of lesion bypass polymerases in ICL repair, we investigated recombination-independent repair of ICLs in REV3 and REV1 deletion mutants constructed in avian DT40 cells and mouse embryonic fibroblast cells. Our results showed that Rev3 plays a major role in recombination-independent ICL repair, which may account for the extreme sensitivity of REV3 mutants to cross-linking agents. This result raised the possibility that the NER gap synthesis, when encountering an adducted base present in the ICL repair intermediate, can lead to recruitment of Rev3, analogous to the recruitment of polymerase eta during replicative synthesis. Indeed, the monoubiquitination-defective Proliferating Cell Nuclear Antigen (PCNA) mutant exhibits impaired recombination-independent ICL repair as well as drastically reduced mutation rate, indicating that the PCNA switch is utilized to enable lesion bypass during DNA repair synthesis. Analyses of a REV1 deletion mutant also revealed a significant reduction in recombination-independent ICL repair, suggesting that Rev1 cooperates with Rev3 in recombination-independent ICL repair. Moreover, deletion of REV3 or REV1 significantly altered the spectrum of mutations resulting from ICL repair, further confirming their involvement in mutagenic repair of ICLs.

Animals↗
PubMed2006

BLAP75/RMI1 promotes the BLM-dependent dissolution of homologous recombination intermediates.

BLM encodes a member of the highly conserved RecQ DNA helicase family, which is essential for the maintenance of genome stability. Homozygous inactivation of BLM gives rise to the cancer predisposition disorder Bloom's syndrome. A common feature of many RecQ helicase mutants is a hyperrecombination phenotype. In Bloom's syndrome, this phenotype manifests as an elevated frequency of sister chromatid exchanges and interhomologue recombination. We have shown previously that BLM, together with its evolutionarily conserved binding partner topoisomerase IIIalpha (hTOPO IIIalpha), can process recombination intermediates that contain double Holliday junctions into noncrossover products by a mechanism termed dissolution. Here we show that a recently identified third component of the human BLM/hTOPO IIIalpha complex, BLAP75/RMI1, promotes dissolution catalyzed by hTOPO IIIalpha. This activity of BLAP75/RMI1 is specific for dissolution catalyzed by hTOPO IIIalpha because it has no effect in reactions containing either Escherichia coli Top1 or Top3, both of which can also catalyze dissolution in a BLM-dependent manner. We present evidence that BLAP75/RMI1 acts by recruiting hTOPO IIIalpha to double Holliday junctions. Implications of the conserved ability of type IA topoisomerases to catalyze dissolution and how the evolution of factors such as BLAP75/RMI1 might confer specificity on the execution of this process are discussed.

Adenosine Triphosphatases↗
PubMed2006

A conserved linear B-cell epitope at the N-terminal region of woodchuck hepatitis virus core protein (WHcAg).

Woodchuck hepatitis virus (WHV) is a member of family Hepadnaviridae and closely related to hepatitis B virus (HBV). The WHV core protein (WHcAg) is a strongly immunogenic protein and forms virus-like particles. WHcAg may represent a suitable carrier system for B- and T-cell epitopes. However, the lack of a high expression system for WHcAg and defined antibodies to detect WHcAg prevents the use of this carrier system. In the present study, vectors expressing WHcAg with carboxyl-terminal truncations were constructed to determine the region of WHcAg required for assembly. The first 144 or 149 amino acid residues of WHcAg were able to efficiently assemble into particulate structures. Both truncated forms of WHcAg were accumulated in E. coli as uniform particles with a diameter of 34nm in large quantities and could be purified in milligram scale. As expected, the particles of truncated WHcAg retained the antigenicity of the full length WHcAg. However, denatured WHcAg remained to be reactive with specific antisera, suggesting that WHcAg may possess additional linear B-cell epitopes. Monoclonal antibodies against denatured WHcAg were generated and tested for their specificity. Five antibodies were found to direct the N-terminal region of WHcAg. Due to the conservation of the amino acid sequence in this region of WHcAg and HBcAg, these antibodies recognized recombinant HBcAg as well. Thus, this linear B-cell epitope is conserved on the core proteins of hepadnaviruses.

Animals↗
PubMed2006

Disruption of PTEN coupling with 5-HT2C receptors suppresses behavioral responses induced by drugs of abuse.

The widespread distribution of the tumor suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10) in the adult brain suggests its role in a broad range of brain functions. Here we show evidence supporting a physical interaction of PTEN with a region in the third intracellular loop (3L4F) of the serotonin 5-HT2C receptor (5-HT2cR, formerly 5-HT1c receptor) in cell cultures. PTEN limits agonist-induced phosphorylation of 5-HT2cR through its protein phosphatase activity. We showed the probable existence of PTEN:5-HT2cR complexes in putative dopaminergic neurons in the rat ventral tegmental area (VTA), a brain region in which virtually all abused drugs exert rewarding effects by activating its dopamine neurons. We synthesized the interfering peptide Tat-3L4F, which is able to disrupt PTEN coupling with 5-HT2cR. Systemic application of Tat-3L4F or the 5-HT2cR agonist Ro600175 suppressed the increased firing rate of VTA dopaminergic neurons induced by delta9-tetrahydrocannabinol (THC), the psychoactive ingredient of marijuana. Using behavioral tests, we found that Tat-3L4F or Ro600175 blocks conditioned place preference of THC or nicotine, and that Ro600175, but not Tat-3L4F, produces anxiogenic effects, penile erection, hypophagia and motor functional suppression. These results suggest a potential strategy for treating drug addiction with the Tat-3L4F peptide.

Animals↗
PubMed2006

Experimental study of recombinant eukaryotic expression vector of human eNOS in ECV304.

BACKGROUND AND PURPOSE: Gene transfer with recombinant non-viral vectors encoding vasodilator proteins, such as endothelial nitric oxide synthase (eNOS), maybe a preferential choice in gene therapy of artery restenosis following angioplasty, stent or anastomosis. However, the transfection rate of a non-viral vector, the harmful effects of eNOS transfection on endothelial cells (EC) and the control release of nitric oxide (NO) have been controversial. We designed the eukaryotic expression vector pcDNA3.1-eNOS to study the regulated expression of eNOS (in the presence of various chemical agents) and to evaluate the exogenous NO effect on EC proliferation in vitro. METHODS: The full-length human eNOS cDNA was inserted into the EcoRI cloning site of the pcDNA3.1 expression plasmid and the eNOS direction was tested by restriction enzyme digestion with XhoI to construct recombinant pcDNA3.1-eNOS. After co-transfection of pcDNA3.1-eNOS with pcDNA3.0-EGFP mediated by cationic liposomes into Human umbilical vein endothelial cells (ECV304), the transfection rate and the effect on ECV304 proliferation were calculated by fluorescence microscopy and flowcytometry. eNOS mRNA and protein were detected by reverse transcription-PCR (RT-PCR) and immunofluorescence, respectively. The eNOS activity, NO release and changes of the relevant cells growth curve were assessed after treating the transfected cells with four independent factors including ie Ca2+, L-arginine (L-Arg), Ethylene Diamine Tetraacetic Acid (EDTA) and N-nitro-L-arginine methylester (L-NAME). In addition, we examined the non-transfected cells status by isolated sodium nitroprusside (SNP) treatment. RESULT: eNOS cDNA was inserted into pcDNA3.1 in the proper direction. RT-PCR analysis showed that pcDNA3.1-eNOS transfected cells could express eNOS mRNA. The rate of eNOS transfection was 39.6 +/- 3.4%. Immunofluorescence staining displayed that subcellular localisation of eNOS was most prominent in plasma membrane and perinuclear regions of the cell. The eNOS activity of eNOS transfected cells had not increased significantly, whereas, in the presence of Ca2+, L-Arg, EDTA, and L-NAME, the eNOS activity was 96.98 +/- 13.47, 32.57 +/- 6.39, 11.63 +/- 3.02, 15.56 L 7.34 U/ml respectively and the NO level was 55.34 +/- 11.19, 9.43 +/- 4.51, 2.63 +/- 1.41, 3.73 +/- 1.65 mmol/L, respectively. Meanwhile, the growth curves of EC shifted. SNP also had obvious growth-inhibiting effects on the cells. Together, the ECV304 growth curve went downward in a NO concentration-dependent manner. CONCLUSION: Eukaryotic expression vector pcDNA3.1-eNOS was constructed successfully with the ability to express human eNOS mRNA and protein in EC effectively. The activity of eNOS in EC could be regulated by certain exogenous factors. Ca2+ was an important factor promoting NO release and excess NO had a cytotoxic effect on EC in vitro. Controlled release of NO in vivo and polygenic measurements might be considered in more clinical gene therapy studies.

Cell Line↗
PubMed2006

Mosquito ribosomal protein S3 lacks a critical glutamine residue associated with DNA repair activity in homologous Drosophila proteins.

In Drosophila melanogaster, ribosomal protein RpS3 has extra-ribosomal activities including apurinic/apyrimidinic lyase activity and N-glycosylase activity that participate in DNA repair. It has been suggested that these activities couple DNA repair to the translational machinery. To establish a basis for participation of RpS3 in DNA repair in mosquitoes, we cloned RpS3 cDNAs from Aedes aegypti and Aedes albopictus mosquito cell lines. The sequence data were used to reconstruct the homologous gene from the Anopheles gambiae database. Mosquito RpS3 is a single copy gene, which in Aedes albopictus, lacks introns in the amino acid coding region. Although RpS3 proteins are well-conserved among eukaryotes, a critical glutamine residue, Q59, essential to robust DNA repair activity in the Drosophila protein, is replaced by an asparagine (N) in all three mosquito RpS3 proteins. In this respect, the mosquito protein resembles human RpS3, which has relatively modest DNA repair activity. None of the insect RpS3 proteins available in the database, other than those from Drosophila, contain glutamine at position 59. However, in the Lepidoptera, N59 is consistently replaced by serine (S), and the putative interactive site at position 134 is replaced by arginine (R). These data suggest that in the case of RpS3, the Drosophila protein may be uniquely unusual in having robust DNA repair activities that are unlikely to be common to RpS3 from other insects.

Aedes↗
PubMed2006

The chemical constituents of the fungus Stereum sp.

Four new compounds, including a sesquiterpene and three aromatic compounds, and a known compound were isolated from a culture broth of the fungus Stereum sp. The novel sesquiterpene was determined to be stereumone A ((+)-2,3,4a,5,6,7,8a,9-octahydro-5-hydroxy-6,6,9-trimethyl-4,8a-epoxynaphtho[2,3-b]furan-8(8H)-one; 1), and the three new aromatic compounds were elucidated as 3,5-dihydroxy-4-(3-methylbut-2-enyl)benzene-1,2-dicarbaldehyde (2), 5,7-dihydroxy-6-(3-methylbut-2-enyl)isobenzofuran-1(3H)-one (3), butyl 2,4-dihydroxy-6-methylbenzoate (4), together with the known compound methyl 2,4-dihydroxy-6-methylbenzoate (5). The structures were established by spectroscopic methods including 2D-NMR techniques. Compounds 2 and 4 showed evident nematicidal activity against nematode Panagrellus redivivus.

Animals↗
PubMed2006

Proteomic analyses of Oryza sativa mature pollen reveal novel proteins associated with pollen germination and tube growth.

As a highly reduced organism, pollen performs specialized functions to generate and carry sperm into the ovule by its polarily growing pollen tube. Yet the molecular genetic basis of these functions is poorly understood. Here, we identified 322 unique proteins, most of which were not reported previously to be in pollen, from mature pollen of Oryza sativa L. ssp japonica using a proteomic approach, 23% of them having more than one isoform. Functional classification reveals that an overrepresentation of the proteins was related to signal transduction (10%), wall remodeling and metabolism (11%), and protein synthesis, assembly and degradation (14%), as well as carbohydrate and energy metabolism (25%). Further, 11% of the identified proteins are functionally unknown and do not contain any conserved domain associated with known activities. These analyses also identified 5 novel proteins by de novo sequencing and revealed several important proteins, mainly involved in signal transduction (such as protein kinases, receptor kinase-interacting proteins, guanosine 5'-diphosphate dissociation inhibitors, C2 domain-containing proteins, cyclophilins), protein synthesis, assembly and degradation (such as prohibitin, mitochondrial processing peptidase, putative UFD1, AAA+ ATPase), and wall remodeling and metabolism (such as reversibly glycosylated polypeptides, cellulose synthase-like OsCsLF7). The study is the first close investigation, to our knowledge, of protein complement in mature pollen, and presents useful molecular information at the protein level to further understand the mechanisms underlying pollen germination and tube growth.

Amino Acid Sequence↗