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

The molar absorption coefficient, E, of a protein is usually based on concentrations measured by dry weight, nitrogen, or amino acid analysis. The studies reported here suggest that the Edelhoch method is the best method for measuring E for a protein. (This method is described by Gill and von Hippel [1989, Anal Biochem 182:3193261 and is based on data from Edelhoch [1967, Biochemistry 6:1948-19541.) The absorbance of a protein at 280 nm depends on the content of Trp, Tyr, and cystine (disulfide bonds). The average E values for these chromophores in a sample of 18 well-characterized proteins have been estimated, and the E values in water, propanol, 6 M guanidine hydrochloride (GdnHCI), and 8 M urea have been measured. For Trp, the average E values for the proteins are less than the E values measured in any of the solvents. For Tyr, the average E values for the proteins are intermediate between those measured in 6 M GdnHCl and those measured in propanol. Based on a sample of 116 measured t values for 80 proteins, the t at 280 nm of a folded protein in water, t(280), can best be predicted with this equation:

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pro.5560041120

How to measure and predict the molar absorption coefficient of a protein.

http://orion.bme.columbia.edu/lulab/pdf/Altman_Silk-Based-Biomaterials_2003.pdf

Silk-based biomaterials

http://ctrstbio.org.uic.edu/manuals/kellybba.pdf

How to study proteins by circular dichroism

Graphite oxide is one of the main precursors of graphene-based materials, which are highly promising for various technological applications because of their unusual electronic properties Although epoxy and hydroxyl groups are widely accepted as its main functionalities, the complete structure of graphite oxide has remained elusive By interpreting spectroscopic data in the context of the major functional groups believed to be present in graphite oxide, we now show evidence for the presence of five- and six-membered-ring lactols On the basis of this chemical composition, we devised a complete reduction process through chemical conversion by sodium borohydride and sulfuric acid treatment, followed by thermal annealing Only small amounts of impurities are present in the final product (less than 05 wt% of sulfur and nitrogen, compared with about 3 wt% with other chemical reductions) This method is particularly effective in the restoration of the π-conjugated structure, and leads to highly soluble and conductive graphene materials

New insights into the structure and reduction of graphite oxide

Spider major ampullate (dragline) silk is an extracellular fibrous protein with unique characteristics of strength and elasticity. The silk fiber has been proposed to consist of pseudocrystalline regions of antiparallel beta-sheet interspersed with elastic amorphous segments. The repetitive sequence of a fibroin protein from major ampullate silk of the spider Nephila clavipes was determined from a partial cDNA clone. The repeating unit is a maximum of 34 amino acids long and is not rigidly conserved. The repeat unit is composed of three different segments: (i) a 6 amino acid segment that is conserved in sequence but has deletions of 3 or 6 amino acids in many of the repeats; (ii) a 13 amino acid segment dominated by a polyalanine sequence of 5-7 residues; (iii) a 15 amino acid, highly conserved segment. The latter is predominantly a Gly-Gly-Xaa repeat with Xaa being alanine, tyrosine, leucine, or glutamine. The codon usage for this DNA is highly selective, avoiding the use of cytosine or guanine in the third position. A model for the physical properties of fiber formation, strength, and elasticity, based on this repetitive protein sequence, is presented.

https://www.pnas.org/content/pnas/87/18/7120.full.pdf

Structure of a protein superfiber: spider dragline silk.

Hypotheses that correlate the sequence, structure, and mechanical properties of spider silk proteins.

Spiders (Araneae) spin high-performance silks from liquid fibroin proteins. Fibroin sequences from basal spider lineages reveal mosaics of amino acid motifs that differ radically from previously described spider silk sequences. The silk fibers of Araneae are constructed from many protein designs. Yet, the repetitive sequences of fibroins from orb-weaving spiders have been maintained, presumably by stabilizing selection, over 125 million years of evolutionary history. The retention of these conserved motifs since the Mesozoic and their convergent evolution in other structural superproteins imply that these sequences are central to understanding the exceptional mechanical properties of orb weaver silks.

https://science.sciencemag.org/content/sci/291/5513/2603.full.pdf

Randolph V. Lewis

Papers

Structure of a protein superfiber: spider dragline silk.

Hypotheses that correlate the sequence, structure, and mechanical properties of spider silk proteins.

Extreme Diversity, Conservation, and Convergence of Spider Silk Fibroin Sequences

Isolation of a clone encoding a second dragline silk fibroin. Nephila clavipes dragline silk is a two-protein fiber.

Statistical determination of the average values of the extinction coefficients of tryptophan and tyrosine in native proteins