Acanthamoeba healyi: expressed gene profiles with enhanced virulence after mouse-brain passage

The virulence of Acanthamoeba can be attenuated by long-term in vitro cultivation, and can be recovered by serial mouse-brain passage via intranasal inoculation. Recovery is concomitant with changes in expression of virulence-related genes. To investigate the virulence factors of Acanthamoeba, expressed sequence tags (ESTs) from two kinds of cDNA libraries-long-term in vitro cultivated A. healyi (OLD) and three times mouse-brain passaged A. healyi (MBP)-were compared using reciprocal BLAST analysis, eukaryotic orthologous groups (KOG) assignment, and gene annotation. A total of 938 (OLD) and 1033 (MBP) ESTs were sequenced and resulted in the assembling of 718 OLD and 833 MBP unique sequences. Comparison of the KOG analysis revealed a relatively higher percentage of MBP ESTs in genes related to transcription (K group), amino acid transport and metabolism (E group), coenzyme transport and metabolism (H group), and secondary metabolites biosynthesis, transport and metabolism (Q group). However, a higher percentage of unidentified MBP ESTs (57.9%) than OLD ESTs (28.9%) was evidence of the limited understanding of virulence-related factors of Acanthamoeba. Characterization of the genes expressed during brain passage in mice will be useful in clarifying the pathogenesis of granulomatous amoebic encephalitis by Acanthamoeba.

Construction of EST database for comparative gene studies of Acanthamoeba

The genus Acanthamoeba can cause severe infections such as granulomatous amebic encephalitis and amebic keratitis in humans. However, little genomic information of Acanthamoeba has been reported. Here, we constructed Acanthamoeba expressed sequence tags (EST) database (Acanthamoeba EST DB) derived from our 4 kinds of Acanthamoeba cDNA library. The Acanthamoeba EST DB contains 3,897 EST generated from amebae under various conditions of long term in vitro culture, mouse brain passage, or encystation, and downloaded data of Acanthamoeba from National Center for Biotechnology Information (NCBI) and Taxonomically Broad EST Database (TBestDB). The almost reported cDNA/genomic sequences of Acanthamoeba provide stand alone BLAST system with nucleotide (BLAST NT) and amino acid (BLAST AA) sequence database. In BLAST results, each gene links for the significant information including sequence data, gene orthology annotations, relevant references, and a BlastX result. This is the first attempt for construction of Acanthamoeba database with genes expressed in diverse conditions. These data were integrated into a database (http://www.amoeba.or.kr).

Induction of thioredoxin is required for nodule development to reduce reactive oxygen species levels in soybean roots

Nodules are formed on legume roots as a result of signaling between symbiotic partners and in response to the activities of numerous genes. We cloned fragments of differentially expressed genes in spot-inoculated soybean (Glycine max) roots. Many of the induced clones were similar to known genes related to oxidative stress, such as thioredoxin and beta-carotene hydroxylase. The deduced amino acid sequences of full-length soybean cDNAs for thioredoxin and beta-carotene hydroxylase were similar to those in other species. In situ RNA hybridization revealed that the thioredoxin gene is expressed on the pericycle of 2-d-old nodules and in the infected cells of mature nodules, suggesting that thioredoxin is involved in nodule development. The thioredoxin promoter was found to contain a sequence resembling an antioxidant responsive element. When a thioredoxin mutant of yeast was transformed with the soybean thioredoxin gene it became hydrogen peroxide tolerant. These observations prompted us to measure reactive oxygen species levels. These were decreased by 3- to 5-fold in 7-d-old and 27-d-old nodules, coincident with increases in the expression of thioredoxin and beta-carotene hydroxylase genes. Hydrogen peroxide-producing regions identified with cerium chloride were found in uninoculated roots and 2-d-old nodules, but not in 7-d-old and 27-d-old nodules. RNA interference-mediated repression of the thioredoxin gene severely impaired nodule development. These data indicate that antioxidants such as thioredoxin are essential to lower reactive oxygen species levels during nodule development.

Hantaan virus enters cells by clathrin-dependent receptor-mediated endocytosis

The cellular entry of Hantaan virus (HTN) occurs through interactions with beta(3) integrins as cellular receptors. However, the process of HTN infection following attachment to the cell surface is not well understood. Our data indicate that overexpression of a dominant-negative mutant dynamin inhibits HTN internalization and that compounds that block clathrin- but not caveolae-dependent endocytosis also reduce HTN infectivity. In addition, we show that HTN colocalizes with the clathrin heavy chain but not with caveolae. At the early phase of infection HTN colocalizes with EEA-1, an early endosome marker, and later, HTN colocalizes with LAMP-1, a lysosome marker. Cells treated with lysosomotropic agents are largely resistant to infection, suggesting that a low-pH-dependent step is required for HTN infection. These findings demonstrate that HTN enters cells via the clathrin-coated pit pathway and uses low-pH-dependent intracellular compartments for infectious entry.

Purification and characterization of the GroESLx chaperonins from the symbiotic X-bacteria in Amoeba proteus

GroELx and GroESx proteins of symbiotic X-bacteria from Amoeba proteus were overproduced in Escherichia coli transformed with pAJX91 and pUXGPRM, respectively, and their chaperonin functions were assayed. We utilized sigma(70)-dependent specific promoters of groEx in the expression vectors and grew recombinant cells at 37 degrees C to minimize coexpression of host groE of E. coli. For purifying the proteins, we applied the principle of heat stability for GroELx and pI difference for GroESx to minimize copurification with the hosts GroEL and GroES, respectively. After ultracentrifugation in a sucrose density gradient, the yield and purity of GroELx were 56 and 89%, respectively. The yield and purity of GroESx after anion-exchange chromatography were 62 and 91%, respectively. Purified GroELx had an ATPase activity of 53.2 nmol Pi released/min/mg protein at 37 degrees C. The GroESx protein inhibited ATPase activity of GroELx to 60% of the control at a ratio of 1 for GroESx-7mer/GroELx-14mer. GroESLx helped refolding of urea-unfolded rhodanese up to 80% of the native activity at 37 degrees C. By chemical cross-linking analysis, oligomeric properties of GroESx and GroELx were confirmed as GroESx(7) and GroELx(14) in two stacks of GroELx(7). In this study, we developed a method for the purification of GroESLx and demonstrated that their chaperonin function is homologous to GroESL of E. coli.

Periplasmic localization of a GroES homologue in Escherichia coli transformed with groESx cloned from Legionella-like endosymbionts in Amoeba proteus

Escherichia coli MC4100 transformed with a groE homologous operon cloned from X-bacteria accumulated large amounts of the gene product when cultured at 30 or 37 degrees C. Heat shock for 10-30 min at 42 degrees C or ethanol (5%) shock for 2 h increased GroESx levels to about twice that in E. coli grown at 30 degrees C. The subcellular localization of GroESx in transformed E. coli was determined by several subcellular fractionation methods, by the analysis of extracted proteins in SDS polyacrylamide gels and by assays of marker enzymes. The GroESx protein was detected in both the periplasmic and cytoplasmic extracts and a large amount of the protein was accumulated in the periplasm. The GroEL protein and recombinant beta-galactosidase were exclusively localized in the cytoplasmic fraction, eliminating the possibility that periplasmic GroESx might be due to simple overproduction. N-terminal amino acid sequencing confirmed that the protein resolved on a 2-D gel was GroESx. This work represents the first report of the periplasmic location of GroES homologues in E. coli.

Characterization of a monoclonal antibody and a cDNA for polyubiquitin of Amoeba proteus

A monoclonal antibody was obtained that reacts with many different proteins (14-200 kDa) of Amoeba proteus. By indirect immunofluorescence microscopy we found the antigens to be dispersed throughout the cytoplasm but were more concentrated in the nucleus. The antibody cross-reacted with proteins of Tetrahymena, Xenopus embryo, and mouse macrophages. Using the antibody as a probe we cloned a cDNA of 1.2 kb coding for ubiquitin in five repeats. Amino acid sequences of ameba's polyubiquitin showed the most variations among the nineteen polyubiquitins of other organisms compared. The well-conserved 20Ser and 55Thr residues were replaced with Gly and Ser, respectively. The 28Ala residue found in most organisms was replaced with Gln or Glu in the amoeba. Amoebae contained two ubiquitin-mRNAs that could be detected by Northern blot analysis using the cDNA as a probe. In an analysis for specificity, the antibody reacted with polyubiquitin and ubiquitin-fusion proteins larger than 14 kDa but not with monomeric ubiquitin. The antibody is a useful probe in the detection and characterization of proteins ubiquitinated in response to cellular stresses.

Evidence for symbiont-induced alteration of a host's gene expression: irreversible loss of SAM synthetase from Amoeba proteus

Symbiont-bearing xD amoebae no longer produce a 45-kDa cytoplasmic protein that functions as S-adenosylmethionine synthetase in symbiont-free D amoebae. The absence of the protein in xD amoebae is attributable to xD amoeba's failure to transcribe the corresponding gene as a result of harboring bacterial symbionts. However, xD amoebae have about half the level of enzyme activity found in D amoebae, indicating that they use an alternative source for the enzyme. xD amoebae originated from D amoebae by bacterial infection and now depend on their symbionts for survival. xD amoebae exhibit irreversible nucleolar abnormalities when their symbionts are removed, suggesting that X-bacteria supply the needed enzyme. A monoclonal antibody against the 45-kDa protein was produced and used as a probe in cloning its corresponding cDNA. The product of the cDNA was found to have S-adenosylmethionine synthetase activity. These results show how symbiotic X-bacteria may become essential cellular components of amoeba by supplementing a genetic defect for an amoeba's house-keeping gene that is brought about by an action of X-bacteria themselves. This is the first reported example in which symbionts alter the host's gene expression to block the production of an essential protein.

A novel strong promoter of the groEx operon of symbiotic bacteria in Amoeba proteus

Gram- symbiotic bacteria (called X-bacteria), present in the xD strain of Amoeba proteus as required cell components, contain a large amount of a 67-kDa protein, a GroEL analog. The complete nucleotide (nt) sequence of the groEx operon of X-bacteria has been determined and it has a high degree of nt identity with those of other bacterial groE operons. The groELx gene is expressed in transformed Escherichia coli and has a novel and potent promoter (P2) in addition to the heat-shock consensus promoter (P1). This is shown by the production of GroELx in Escherichia coli transformed with modified DNA clones lacking P1 and by an enhanced production of a GroELx::beta-galactosidase fusion protein when a portion of groEx containing P2 is linked to the lacZ gene. Primer-extension analyses revealed the presence of possible P2 sequences within the open reading frame of the groESx gene. It is suggested that the presence of a potent P2 in the X-bacterial gene is an adaptation for the endosymbiotic bacteria to survive within a potentially hostile intracellular environment.

Antigenic reactivity of a monoclonal antibody against Amoeba proteus actin

The reactivity of a monoclonal antibody against actin of Amoeba proteus with actins from other sources was examined. The monoclonal antibody cross-reacted with actins from vertebrate muscles, human erythrocytes, and Acanthamoeba castellanii, but it did not react with Naegleria gruberi actin. The amoeba actin was resolved into 3 bands with isoelectric points of 5.96, 6.03 and 6.10 in electrofocusing gels and they corresponded to 3 peptide spots reacting with the antibody on 2-dimensional immunoblots.

Recycling of membrane proteins during endo- and exocytosis in amoebae

The fate of a membrane protein of the amoeba plasmalemma was studied by means of 125I iodination by lactoperoxidase, gel electrophoresis, radioautography and gamma counting. There was only one iodinatable polypeptide group with a molecular weight (MW) of 175 000 on the external surface of the plasmalemma. Two hours or more after induced phagocytosis, isolated phagolysosomal membranes contained two other smaller polypeptides with MWs of 70 000 and 35 000, respectively, suggesting that the 175 000 polypeptide was broken down to these smaller components during endocytosis. After 22 h of induced phagocytosis, isolated plasmalemma contained a 35 000 polypeptide group in addition to the 175 000 polypeptide species. The results suggested that some of the iodinatable membrane proteins were altered and recycled during endo- and exocytosis in amoebae, while others were recycled intact.

Growth and electron microscopic studies on an experimentally established bacterial endosymbiosis in amoebae

A strain of nonsymbiotic A. proteus was infected with endosymbiotic bacteria isolated from another strain of amoeba which had become dependent on the symbionts after a few years of spontaneously established symbiosis. In the newly infected amoebae, the bacteria avoided digestion and multiplied at a faster rate than the hosts, reaching the maximum carrying number (about 42,000 per amoeba) in fewer than ten cell generations of the hosts. The experimentally infected amoebae were also examined under the electron microscope, and the development of bacteria-containing vesicles was followed. The results show that the infective bacteria that were initially harmful to host amoebae have become harmless and that they have changed in their mode of multiplication during the course of establishing a stable symbiosis with their hosts.

Temperature Sensitivity: A Cell Character Determined by Obligate Endosymbionts in Amoebas

A strain of Amoeba proteus has lost its ability to survive at temperatures above 26 degrees C as a result of becoming dependent on endosymbiotic bacteria that are psychrophile-like. The observed temperature sensitivity develops in fewer than 200 host cell generations (18 months of culture) after the host cells are experimentally infected with the symbionts.