Antagonistic experimental coevolution with a parasite increases host recombination frequency

Background  

One of the big remaining challenges in evolutionary biology is to understand the evolution and maintenance of meiotic recombination. As recombination breaks down successful genotypes, it should be selected for only under very limited conditions. Yet, recombination is very common and phylogenetically widespread. The Red Queen Hypothesis is one of the most prominent hypotheses for the adaptive value of recombination and sexual reproduction. The Red Queen Hypothesis predicts an advantage of recombination for hosts that are coevolving with their parasites. We tested predictions of the hypothesis with experimental coevolution using the red flour beetle, Tribolium castaneum, and its microsporidian parasite, Nosema whitei.     

No evidence from FTIR difference spectroscopy that aspartate-170 of the D1 polypeptide ligates a manganese ion that undergoes oxidation during the S0 to S1, S1 to S2, or S2 to S3 transitions in photosystem II

On the basis of mutagenesis and X-ray crystallographic studies, Asp170 of the D1 polypeptide is widely believed to ligate the (Mn)4 cluster that is located at the catalytic site of water oxidation in photosystem II. Recent proposals for the mechanism of water oxidation postulate that D1-Asp170 ligates a Mn ion that undergoes oxidation during one or more of the S0 --> S1, S1 --> S2, and S2 --> S3 transitions. To test these hypotheses, we have compared the FTIR difference spectra of the individual S state transitions in wild-type* PSII particles from the cyanobacterium Synechocystis sp. PCC 6803 with those in D1-D170H mutant PSII particles. Remarkably, our data show that the D1-D170H mutation does not significantly alter the mid-frequency regions (1800-1000 cm(-1)) of any of the FTIR difference spectra. Therefore, we conclude that the oxidation of the (Mn)4 cluster does not alter the frequencies of the carboxylate stretching modes of D1-Asp170 during the S0 --> S1, S1 --> S2, or S2 --> S3 transitions. The simplest explanation for these data is that the Mn ion that is ligated by D1-Asp170 does not increase its charge or oxidation state during any of these S state transitions. These data have profound implications for the mechanism of water oxidation. Either (1) the oxidation of the Mn ion that is ligated by D1-Asp170 occurs only during the transitory S3 --> S4 transition and serves as the critical step in the ultimate formation of the O-O bond or (2) the oxidation increments and O2 formation chemistry that occur during the catalytic cycle involve only the remaining Mn3Ca portion of the Mn4Ca cluster. Our data also show that, if the increased positive charge on the (Mn)4 cluster that is produced during the S1 --> S2 transition is delocalized over the (Mn)4 cluster, it is not delocalized onto the Mn ion that is ligated by D1-Asp170.     

Trypanosoma congolense: structure and molecular organization of the surface glycoproteins of two early bloodstream variants

The complete primary structures of two variant specific glycoproteins (VSGs) of the nannomonad Trypanosoma (N.) congolense are presented. These coat proteins subserve the function of antigenic variation. The secondary structure potentials of both VSGs have been calculated. The amino acid sequences and secondary structure potentials of these VSGs have been compared with the primary structures and secondary structure potentials of several Trypanosoma brucei complex VSGs. In homologous regions, the T. brucei complex VSGs show a pattern of sharply contrasting secondary structure potentials. It has been suggested previously that this pattern gives rise to different folding structures in different members of this polygene protein family. Thus, different short regions of the polypeptide sequence are exposed as antigenic "caps" on the solvent-exposed surface of intact trypanosomes. A sharply contrasting secondary structure potential pattern is also found in regions of the two T. congolense VSGs. However, there is little homology of primary structure between each of the two T. congolense VSGs and any member of the T. brucei complex VSG polygene family whose primary structure has been determined.     

Plant as a plenteous reserve of lectin

Lectins are clusters of glycoproteins of nonimmune foundation that combine specifically and reversibly to carbohydrates, mainly the sugar moiety of glycoconjugates, resulting in cell agglutination and precipitation of glycoconjugates. They are universally distributed in nature, being established in plants, fungi, viruses, bacteria, crustacea, insects, and animals, but leguminacae plants are rich source of lectins. The present review reveals the structure, biological properties, and application of plant lectins.