抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

High-affinity nucleic acid ligands for a protein were isolated by a procedure that depends on alternate cycles of ligand selection from pools of variant sequences and amplification of the bound species. Multiple rounds exponentially enrich the population for the highest affinity species that can be clonally isolated and characterized. In particular one eight-base region of an RNA that interacts with the T4 DNA polymerase was chosen and randomized. Two different sequences were selected by this procedure from the calculated pool of 65,536 species. One is the wild-type sequence found in the bacteriophage mRNA; one is varied from wild type at four positions. The binding constants of these two RNA's to T4 DNA polymerase are equivalent. These protocols with minimal modification can yield high-affinity ligands for any protein that binds nucleic acids as part of its function; high-affinity ligands could conceivably be developed for any target molecule.

https://science.sciencemag.org/content/sci/249/4968/505.full.pdf

Systematic evolution of ligands by exponential enrichment: RNA ligands to bacteriophage T4 DNA polymerase

Subpopulations of RNA molecules that bind specifically to a variety of organic dyes have been isolated from a population of random sequence RNA molecules. Roughly one in 10(10) random sequence RNA molecules folds in such a way as to create a specific binding site for small ligands.

In vitro selection of RNA molecules that bind specific ligands.

On the Nature of Allosteric Transitions: A Plausible Model

Rechargeable solid-state batteries have long been considered an attractive power source for a wide variety of applications, and in particular, lithium-ion batteries are emerging as the technology of choice for portable electronics. One of the main challenges in the design of these batteries is to ensure that the electrodes maintain their integrity over many discharge-recharge cycles. Although promising electrode systems have recently been proposed, their lifespans are limited by Li-alloying agglomeration or the growth of passivation layers, which prevent the fully reversible insertion of Li ions into the negative electrodes. Here we report that electrodes made of nanoparticles of transition-metal oxides (MO, where M is Co, Ni, Cu or Fe) demonstrate electrochemical capacities of 700 mA h g(-1), with 100% capacity retention for up to 100 cycles and high recharging rates. The mechanism of Li reactivity differs from the classical Li insertion/deinsertion or Li-alloying processes, and involves the formation and decomposition of Li2O, accompanying the reduction and oxidation of metal nanoparticles (in the range 1-5 nanometres) respectively. We expect that the use of transition-metal nanoparticles to enhance surface electrochemical reactivity will lead to further improvements in the performance of lithium-ion batteries.

Nano-sized transition-metal oxides as negative-electrode materials for lithium-ion batteries

The DNA of higher organisms usually falls into two classes, one specific and the other comparatively nonspecific. It seems plausible that most of the latter originates by the spreading of sequences which had little or no effect on the phenotype. We examine this idea from the point of view of the natural selection of preferred replicators within the genome.

Selfish DNA: the ultimate parasite

https://www.pnas.org/content/pnas/49/4/517.full.pdf

The maintenance of the accuracy of protein synthesis and its relevance to ageing

The demonstration that ribosomal peptide synthesis is a ribozyme-catalyzed reaction makes it almost certain that there was once an RNA World. The central problem for origin-of-life studies, therefore, is to understand how a protein-free RNA World became established on the primitive Earth. We first review the literature on the prebiotic synthesis of the nucleotides, the nonenzymatic synthesis and copying of polynucleotides, and the selection of ribozyme catalysts of a kind that might have facilitated polynucleotide replication. This leads to a brief outline of the Molecular Biologists' Dream, an optimistic scenario for the origin of the RNA World. In the second part of the review we point out the many unresolved problems presented by the Molecular Biologists' Dream. This in turn leads to a discussion of genetic systems simpler than RNA that might have “invented” RNA. Finally, we review studies of prebiotic membrane formation.

/pdf/prebiotic-chemistry-and-the-origin-of-the-rna-world-43tk55t5qu.pdf

Prebiotic Chemistry and the Origin of the RNA World

Evolution of the genetic apparatus.

Most theories of the origin of biological organization assume that polymers with lengths in the range of 30-60 monomers are needed to make a genetic system viable. But it has not proved possible to synthesize plausibly prebiotic polymers this long by condensation in aqueous solution, because hydrolysis competes with polymerization. The potential of mineral surfaces to facilitate prebiotic polymerization was pointed out long ago. Here we describe a system that models prebiotic polymerization by the oligomerization of activated monomers -both nucleotides and amino acids. We find that whereas the reactions in solution produce only short oligomers (the longest typically being a 10-mer), the presence of mineral surfaces (montmorillonite for nucleotides, illite and hydroxylapatite for amino adds) induces the formation of oligomers up to 55 monomers long. These are formed by successive "feedings" with the monomers; polymerization takes place on the mineral surfaces in a manner akin to solid-phase synthesis of biopolymers.

/pdf/synthesis-of-long-prebiotic-oligomers-on-mineral-surfaces-1zqt7d1rhf.pdf

Leslie E. Orgel

Papers

Selfish DNA: the ultimate parasite

The maintenance of the accuracy of protein synthesis and its relevance to ageing

Prebiotic Chemistry and the Origin of the RNA World

Evolution of the genetic apparatus.

Synthesis of long prebiotic oligomers on mineral surfaces