Hepatitis B polypeptide vaccine preparation in micelle form

The immunoprophylaxis of hepatitis B is hampered by the lack of a technique for growing hepatitis B virus (HBV) in tissue culture. Plasma from persistently infected individuals, one source of viral antigen, contains characteristic 22-nm spherical particles which share a common antigen (the hepatitis B surface antigen or HBsAg) with the outer envelope of the 42-nm double-shelled DNA virus. Highly purified inactivated 22-nm particles have been shown to be safe and to confer protective immunity against HBV in a recent large-scale clinical trial. We have already described the extraction from the particles of a complex of two proteins which are antigenic determinants of HBV--the polypeptide with molecular weight (MW) between 22,000 and 24,000 (called p23) and the glycosylated polypeptide (called gp28) with MW in the range 26,000--29,000 which is thought to be the glycosylated form of p23. We now report the preparation from this complex of water-soluble protein micelles which may be a suitable basis for a second-generation hepatitis B vaccine.     

A steady-state superradiant laser with less than one intracavity photon

The spectral purity of an oscillator is central to many applications, such as detecting gravity waves, defining the second, ground-state cooling and quantum manipulation of nanomechanical objects, and quantum computation. Recent proposals suggest that laser oscillators which use very narrow optical transitions in atoms can be orders of magnitude more spectrally pure than present lasers. Lasers of this high spectral purity are predicted to operate deep in the 'bad-cavity', or superradiant, regime, where the bare atomic linewidth is much less than the cavity linewidth. Here we demonstrate a Raman superradiant laser source in which spontaneous synchronization of more than one million rubidium-87 atomic dipoles is continuously sustained by less than 0.2 photons on average inside the optical cavity. By operating at low intracavity photon number, we demonstrate isolation of the collective atomic dipole from the environment by a factor of more than ten thousand, as characterized by cavity frequency pulling measurements. The emitted light has a frequency linewidth, measured relative to the Raman dressing laser, that is less than that of single-particle decoherence linewidths and more than ten thousand times less than the quantum linewidth limit typically applied to 'good-cavity' optical lasers, for which the cavity linewidth is much less than the atomic linewidth. These results demonstrate several key predictions for future superradiant lasers, which could be used to improve the stability of passive atomic clocks and which may lead to new searches for physics beyond the standard model.     

Biochemical defects in ABCR protein variants associated with human retinopathies

Mutations in the gene encoding ABCR (ABCA4), a photoreceptor-specific ATP-binding cassette (ABC) transporter, are responsible for autosomal recessive Stargardt disease (STGD), an early onset macular degeneration, and some forms of autosomal recessive cone-rod dystrophy and autosomal recessive retinitis pigmentosa. Heterozygosity for ABCA4 mutations may also represent a risk factor for age-related macular degeneration (AMD), although this idea is controversial. An ongoing challenge in the analysis of ABCA4-based retinopathies arises from the observation that most of the ABCA4 sequence variants identified so far are missense mutations that are rare in both patient and control populations. With the current sample size of most sequence variants, one cannot determine statistically whether a particular sequence variant is pathogenic or neutral. A related challenge is to determine the degree to which each pathogenic variant impairs ABCR function, as genotype-phenotype analyses indicate that age of onset and disease severity correlate with different ABCA4 alleles. To address these questions, we performed a functional analysis of human ABCR and its variants. These experiments reveal a wide spectrum of biochemical defects in these variants and provide insight into the transport mechanism of ABCR.     

SecA,a remarkable nanomachine

Biological cells harbor a variety of molecular machines that carry out mechanical work at the nanoscale. One of these nanomachines is the bacterial motor protein SecA which translocates secretory proteins through the protein-conducting membrane channel SecYEG. SecA converts chemically stored energy in the form of ATP into a mechanical force to drive polypeptide transport through SecYEG and across the cytoplasmic membrane. In order to accommodate a translocating polypeptide chain and to release transmembrane segments of membrane proteins into the lipid bilayer, SecYEG needs to open its central channel and the lateral gate. Recent crystal structures provide a detailed insight into the rearrangements required for channel opening. Here, we review our current understanding of the mode of operation of the SecA motor protein in concert with the dynamic SecYEG channel. We conclude with a new model for SecA-mediated protein translocation that unifies previous conflicting data.     

The receptors and cells for mammalian taste

The emerging picture of taste coding at the periphery is one of elegant simplicity. Contrary to what was generally believed, it is now clear that distinct cell types expressing unique receptors are tuned to detect each of the five basic tastes: sweet, sour, bitter, salty and umami. Importantly, receptor cells for each taste quality function as dedicated sensors wired to elicit stereotypic responses.     

灰铸铁的应力屈服曲面及其三维热弹塑性应力解析

对原有的灰铸铁件应力屈服曲面进行了合理的简化,使其在理论上合理,工程应用上更为方便。建立了灰铸铁件三维非稳态热弹塑性应力场的有限元方法。以灰铸铁哑铃件为对象,用新屈服曲面对其应力发展过程进行了模拟,且比较了用新旧屈服面计算得到的结果。