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

Macrophages display remarkable plasticity and can change their physiology in response to environmental cues. These changes can give rise to different populations of cells with distinct functions. In this Review we suggest a new grouping of macrophage populations based on three different homeostatic activities - host defence, wound healing and immune regulation. We propose that similarly to primary colours, these three basic macrophage populations can blend into various other 'shades' of activation. We characterize each population and provide examples of macrophages from specific disease states that have the characteristics of one or more of these populations.

/pdf/exploring-the-full-spectrum-of-macrophage-activation-b5rnrcgcen.pdf

Exploring the full spectrum of macrophage activation.

Overlapping complementary DNA clones were isolated from epithelial cell libraries with a genomic DNA segment containing a portion of the putative cystic fibrosis (CF) locus, which is on chromosome 7 Transcripts, approximately 6500 nucleotides in size, were detectable in the tissues affected in patients with CF The predicted protein consists of two similar motifs, each with (i) a domain having properties consistent with membrane association and (ii) a domain believed to be involved in ATP (adenosine triphosphate) binding A deletion of three base pairs that results in the omission of a phenylalanine residue at the center of the first predicted nucleotide-binding domain was detected in CF patients

https://science.sciencemag.org/content/sci/245/4922/1066.full.pdf

Identification of the cystic fibrosis gene: cloning and characterization of complementary DNA.

The contribution of tumorigenic stem cells to haematopoietic cancers has been established for some time, and cells possessing stem-cell properties have been described in several solid tumours. Although chemotherapy kills most cells in a tumour, it is believed to leave tumour stem cells behind, which might be an important mechanism of resistance. For example, the ATP-binding cassette (ABC) drug transporters have been shown to protect cancer stem cells from chemotherapeutic agents. Gaining a better insight into the mechanisms of stem-cell resistance to chemotherapy might therefore lead to new therapeutic targets and better anticancer strategies.

/pdf/tumour-stem-cells-and-drug-resistance-210hrtgy2n.pdf

Tumour stem cells and drug resistance

A newly described coronavirus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is the causative agent of coronavirus disease 2019 (COVID-19), has infected over 2.3 million people, led to the death of more than 160,000 individuals and caused worldwide social and economic disruption1,2. There are no antiviral drugs with proven clinical efficacy for the treatment of COVID-19, nor are there any vaccines that prevent infection with SARS-CoV-2, and efforts to develop drugs and vaccines are hampered by the limited knowledge of the molecular details of how SARS-CoV-2 infects cells. Here we cloned, tagged and expressed 26 of the 29 SARS-CoV-2 proteins in human cells and identified the human proteins that physically associated with each of the SARS-CoV-2 proteins using affinity-purification mass spectrometry, identifying 332 high-confidence protein–protein interactions between SARS-CoV-2 and human proteins. Among these, we identify 66 druggable human proteins or host factors targeted by 69 compounds (of which, 29 drugs are approved by the US Food and Drug Administration, 12 are in clinical trials and 28 are preclinical compounds). We screened a subset of these in multiple viral assays and found two sets of pharmacological agents that displayed antiviral activity: inhibitors of mRNA translation and predicted regulators of the sigma-1 and sigma-2 receptors. Further studies of these host-factor-targeting agents, including their combination with drugs that directly target viral enzymes, could lead to a therapeutic regimen to treat COVID-19. A human–SARS-CoV-2 protein interaction map highlights cellular processes that are hijacked by the virus and that can be targeted by existing drugs, including inhibitors of mRNA translation and predicted regulators of the sigma receptors.

/pdf/a-sars-cov-2-protein-interaction-map-reveals-targets-for-5d1m2n6hc1.pdf

A SARS-CoV-2 protein interaction map reveals targets for drug repurposing.

Heterotrimeric guanine nucleotide-binding regulatory proteins (G proteins) dissociate into guanosine triphosphate (GTP)-bound alpha subunits and a complex of beta and gamma subunits after interaction with receptors. The GTP-alpha subunit complex activates appropriate effectors, such as adenylyl cyclase, retinal phosphodiesterase, phospholipase C, and ion channels. G protein beta gamma subunits have been found to have regulatory effects on certain types of adenylyl cyclase. In the presence of Gs alpha, the alpha subunit of the G protein that activates adenylyl cyclase, one form of adenylyl cyclase was inhibited by beta gamma, some forms were activated by beta gamma, and some forms were not affected by beta gamma. These interactions suggest mechanisms for communication between distinct signal-transducing pathways.

https://science.sciencemag.org/content/sci/254/5037/1500.full.pdf

Type-Specific Regulation of Adenylyl Cyclase by G Protein βγ Subunits

Complementary DNA's that encode an adenylyl cyclase were isolated from a bovine brain library. Most of the deduced amino acid sequence of 1134 residues is divisible into two alternating sets of hydrophobic and hydrophilic domains. Each of the two large hydrophobic domains appears to contain six transmembrane spans. Each of the two large hydrophilic domains contains a sequence that is homologous to a single cytoplasmic domain of several guanylyl cyclases; these sequences may represent nucleotide binding sites. An unexpected topographical resemblance between adenylyl cyclase and various plasma membrane channels and transporters was observed. This structural complexity suggests possible, unappreciated functions for this important enzyme.

https://science.sciencemag.org/content/sci/244/4912/1558.full.pdf

Adenylyl cyclase amino acid sequence: possible channel- or transporter-like structure.

Expression and characterization of calmodulin-activated (type I) adenylylcyclase

Oedema factor, a calmodulin-activated adenylyl cyclase, is important in the pathogenesis of anthrax. Here we report the X-ray structures of oedema factor with and without bound calmodulin. Oedema factor shares no significant structural homology with mammalian adenylyl cyclases or other proteins. In the active site, 3′-deoxy-ATP and a single metal ion are well positioned for catalysis with histidine 351 as the catalytic base. This mechanism differs from the mechanism of two-metal-ion catalysis proposed for mammalian adenylyl cyclases. Four discrete regions of oedema factor form a surface that recognizes an extended conformation of calmodulin, which is very different from the collapsed conformation observed in other structures of calmodulin bound to effector peptides. On calmodulin binding, an oedema factor helical domain of relative molecular mass 15,000 undergoes a 15 A translation and a 30° rotation away from the oedema factor catalytic core, which stabilizes a disordered loop and leads to enzyme activation. These allosteric changes provide the first molecular details of how calmodulin modulates one of its targets.

Wei-Jen Tang

Papers

Type-Specific Regulation of Adenylyl Cyclase by G Protein βγ Subunits

Adenylyl cyclase amino acid sequence: possible channel- or transporter-like structure.

Expression and characterization of calmodulin-activated (type I) adenylylcyclase

Structural basis for the activation of anthrax adenylyl cyclase exotoxin by calmodulin.

Distinct patterns of bidirectional regulation of mammalian adenylyl cyclases.