Structure of D-ribulose-l,5-bisphosphate carboxylase/oxygenase from Alcaligenes eutrophyus H16

RuBPcase, D-ribulose-1,5-bisphosphate carboxylase/oxygenase (EC4.1.1.39) is the key enzyme of the reductive pentose phosphate cycle. Because of its biological significance, many structural studies on a number of plant and bacterial RuBPCases have been undertaken, including the enzyme isolated from the autotrophic hydrogen-oxidizing bacterium Alcaligenes eutrophus H16 (refs 2-6). Although both the higher plant enzyme and the A. eutrophus enzyme consist of eight large and eight small subunits (L(8)S(8)), no model describing the quaternary structure is generally accepted. Here we present a model for the A. eutrophus RuBPCase derived from X-ray crystallography of three-dimensional (3D) crystals, and electron microscopy and image analysis of two-dimensional (2D) crystals of the enzyme. The X-ray electron density of RuBPCase in the presence of HCO(-)(3), Mg(2+), and the transition state analogue 2-carboxyarabinitol-1,5-bisphosphate (CABP) shows an L(8)S(8) molecule in which the L(4)S(4) half molecules have local 4-fold symmetry (C4). The local 4-fold axes of the two L(4)S(4) halves do not coincide but are shifted by 36 ? and are related by a crystallographic 2-fold axis perpendicular to and between the local 4-fold axes. Electron microscope data of the enzyme without CABP, which can be perfectly modelled using the X-ray densities, do not show this shift and the low-resolution point group of the molecules in the 2D crystals is D4. Both structures are presented.     

Cyclic dermal BMP signalling regulates stem cell activation during hair regeneration

In the age of stem cell engineering it is critical to understand how stem cell activity is regulated during regeneration. Hairs are mini-organs that undergo cyclic regeneration throughout adult life, and are an important model for organ regeneration. Hair stem cells located in the follicle bulge are regulated by the surrounding microenvironment, or niche. The activation of such stem cells is cyclic, involving periodic beta-catenin activity. In the adult mouse, regeneration occurs in waves in a follicle population, implying coordination among adjacent follicles and the extrafollicular environment. Here we show that unexpected periodic expression of bone morphogenetic protein 2 (Bmp2) and Bmp4 in the dermis regulates this process. This BMP cycle is out of phase with the WNT/beta-catenin cycle, thus dividing the conventional telogen into new functional phases: one refractory and the other competent for hair regeneration, characterized by high and low BMP signalling, respectively. Overexpression of noggin, a BMP antagonist, in mouse skin resulted in a markedly shortened refractory phase and faster propagation of the regenerative wave. Transplantation of skin from this mutant onto a wild-type host showed that follicles in donor and host can affect their cycling behaviours mutually, with the outcome depending on the equilibrium of BMP activity in the dermis. Administration of BMP4 protein caused the competent region to become refractory. These results show that BMPs may be the long-sought 'chalone' inhibitors of hair growth postulated by classical experiments. Taken together, results presented in this study provide an example of hierarchical regulation of local organ stem cell homeostasis by the inter-organ macroenvironment. The expression of Bmp2 in subcutaneous adipocytes indicates physiological integration between these two thermo-regulatory organs. Our findings have practical importance for studies using mouse skin as a model for carcinogenesis, intra-cutaneous drug delivery and stem cell engineering studies, because they highlight the acute need to differentiate supportive versus inhibitory regions in the host skin.     

Determination of ancestral alleles for human single-nucleotide polymorphisms using high-density oligonucleotide arrays.

Here we report the application of high-density oligonucleotide array (DNA chip)-based analysis to determine the distant history of single nucleotide polymorphisms (SNPs) in current human populations. We analysed orthologues for 397 human SNP sites (identified in CEPH pedigrees from Amish, Venezuelan and Utah populations) from 23 common chimpanzee, 19 pygmy chimpanzee and 11 gorilla genomic DNA samples. From this data we determined 214 proposed ancestral alleles (the sequence found in the last common ancestor of humans and chimpanzees). In a diverse human population set, we found that SNP alleles with higher frequencies were more likely to be ancestral than less frequently occurring alleles. There were, however, exceptions. We also found three shared human/pygmy chimpanzee polymorphisms, all involving CpG dinucleotides, and two shared human/gorilla polymorphisms, one involving a CpG dinucleotide. We demonstrate that microarray-based assays allow rapid comparative sequence analysis of intra- and interspecies genetic variation.     

The censoring of Galileo’s Sunspot Letters and the first phase of his trial

Galileo’s Sunspot Letters, published in 1613, underwent extensive censorship before publication. It seems likely that the Roman Inquisition had charge of the pre-publication review of Galileo’s work, rather than the usual organ, the Master of the Sacred Palace. A study of that process demonstrates that the issue to which the censors objected was Galileo’s use of the bible, not his allegiance to Copernicus. In the course of the first phase of Galileo’s trial, orchestrated by one of the most powerful Cardinal Inquisitors, two propositions allegedly drawn from the book were judged either “formally heretical” or “at least erroneous in the faith.” These judgments might have come not from the published book but from the Inquisition’s censorship of its drafts. They supported Galileo’s silencing in 1616.     

Bimodal expression of Sprouty2 during the cell cycle is mediated by phase-specific Ras/MAPK and c-Cbl activities

Sprouty2 is an important inhibitor of cell proliferation and signal transduction. In this study, we found a bimodal expression of Sprouty2 protein during cell cycle progression after exit from quiescence, whereas elevated Sprouty4 expression in the G1 phase stayed high throughout the rest of the cell cycle. Induction of the mitogen-activated protein kinase via activated Ras was crucial for increased Sprouty2 expression at the G0/G1 transition. Following the first peak, accelerated proteasomal protein degradation caused a transient attenuation of Sprouty2 abundance during late G1. Since the decline in its expression was abolished by dominant negative c-Cbl and the timely restricted interaction between Sprouty2 and c-Cbl disappeared at the second peak of Sprouty2 expression, we conclude that the second phase in the cell cycle-specific expression profile of Sprouty2 is solely dependent on ubiquitination by c-Cbl. Our results suggest that Sprouty2 abundance is the result of strictly coordinated activities of Ras and c-Cbl.     

多梯度复杂图像的分割

图像分割是一种重要的图像分析技术,它不仅得到人们广泛的重视和研究,也在实际中得到大量的应用。本文针对一些经典分割算法对多梯度复杂图像分割边缘定位不准确,易受噪声干扰的特点,提出了一种利用图像边缘区域对多梯度复杂图像进行自适应阈值分割的算法。通过对各种算法的比较,本算法抗干扰能力较强,稳定性好,而且完全自动,不需预先设定任何参数。对多种图像的实验表明本文方法十分有效。     

以专业实验室评估为契机积极推进学生素质教育

教育的目的就是为了全面提高人的素质，为适应素质教育的需要，积极推进专业实验室评估势在必行。本文就我院当前形势，结合专业实验室评估的实际工作，对以专业实验室评估为契机积极推进学生素质教育进行了深入的剖析。     

Structure of mammalian AMPK and its regulation by ADP

The heterotrimeric AMP-activated protein kinase (AMPK) has a key role in regulating cellular energy metabolism; in response to a fall in intracellular ATP levels it activates energy-producing pathways and inhibits energy-consuming processes. AMPK has been implicated in a number of diseases related to energy metabolism including type 2 diabetes, obesity and, most recently, cancer. AMPK is converted from an inactive form to a catalytically competent form by phosphorylation of the activation loop within the kinase domain: AMP binding to the γ-regulatory domain promotes phosphorylation by the upstream kinase, protects the enzyme against dephosphorylation, as well as causing allosteric activation. Here we show that ADP binding to just one of the two exchangeable AXP (AMP/ADP/ATP) binding sites on the regulatory domain protects the enzyme from dephosphorylation, although it does not lead to allosteric activation. Our studies show that active mammalian AMPK displays significantly tighter binding to ADP than to Mg-ATP, explaining how the enzyme is regulated under physiological conditions where the concentration of Mg-ATP is higher than that of ADP and much higher than that of AMP. We have determined the crystal structure of an active AMPK complex. The structure shows how the activation loop of the kinase domain is stabilized by the regulatory domain and how the kinase linker region interacts with the regulatory nucleotide-binding site that mediates protection against dephosphorylation. From our biochemical and structural data we develop a model for how the energy status of a cell regulates AMPK activity.