The accessory function of murine intercellular adhesion molecule-1 in T lymphocyte activation. Contributions of adhesion and co-activation.

These studies demonstrate that the murine intercellular adhesion molecule-1 (ICAM-1) performs at least two roles in enhancing T cell activation. These two roles are evident in both of our experimental systems: with ICAM-1 expressed on the surface of transfected fibroblast cells, and with purified ICAM-1 immobilized on plastic. First, as has been documented by many investigators, ICAM-1 mediates adhesion between ICAM-1- and lymphocyte function-associated Ag-1 (LFA-1)-bearing cells. This adhesive interaction occurs even in the absence of T cell stimulation, although it is increased by addition of phorbol ester and calcium ionophore. Although ICAM-1 expression does markedly increase intercellular adhesion, the increase is significantly less than the improvement ICAM-1 expression makes in the Ag-presenting ability of MHC class II-transfected fibroblast cells. We have investigated whether this difference is due to LFA-1-mediated signaling, and we present data that demonstrates that although ICAM-1 does not deliver costimulatory signals required for T cell activation, the interaction of LFA-1 with ICAM-1 does synergize with TCR-transduced signals. This synergy is observed for ICAM-1 on live and on chemically fixed accessory cells, and for purified ICAM-1 molecules, but in all cases occurs only when the ICAM-1 and the TCR ligands are on the same surface. Finally, when the ICAM-1 is present on the surface of accessory cells, it enhances T cell activation by changing the Ag dose-dependence of the T cell, but when ICAM-1 and CD3 mAb are co-immobilized, ICAM-1 increases the peak response of the T cell without affecting the dose dependence of the response.     

羊草与其主要伴生种竞争与共存的格局分析

在羊草种群与其它植物种群的交错区,应用频度、格避形式,格局强度指数对羊草及其主要伴生种之间的共存格局进行了分析。结果表明,羊草及其主要伴生种的格局呈多样化,集聚格局形式是羊草抵御外来物种入侵,或者是自身扩散的一种对策,羊草与其主要伴生种之间存在竞争与共存作用,羊草与芦苇之间通过拮抗作用实现竞争与共存,羊草与鸡儿肠通过竞争而实现共存,光稃茅香,碱茅以营养繁殖策略实现与羊草竞争,指子茅的生长受羊草竞争的抑制。     

MR弥散加权成像对鉴别诊断良恶性椎体压缩性骨折的临床价值研究

目的：探讨MR弥散加权成像（DWI）鉴别诊断良恶性椎体压缩性骨折的临床价值。方法：对57例经临床或病理证实的椎体良恶性压缩性骨折患者行矢状位T1M、T2WI、T2WI／FS及DWI扫描,研究其在常规序列和DWI序列上的表现,将常规MR序列和DWI序列检出率进行比较,测量正常椎体及病变椎体的表观弥散系数（ADC）值,并进行统计学分析。结果：（1）MR常规序列和DWI序列（b=500s／mm2）表现：良性椎体压缩性骨折呈长T1长或等T2改变,T2WI／FS呈高信号,DWI可以呈高信号、等信号及低信号;恶性椎体压缩性骨折呈长T1长T2信号,大部分病灶T2WUFS及DWI呈高信号,少数变现为低信号;（2）MR常规序列和DWI序列（b=500s／mm2）病灶检出率的比较：T1WI、T2WI／FS及DWI序列病灶检出率均高于T2WI序列,其间的差别有显著性意义（P〈0．01）,T1WI、T2WI／FS及DWI序列病灶检出率之间无显著性差异（P〉0．01）;（3）ADC值比较：在DWI（b=500s／mm2）上,良性组ADC值为（2．03±0．83）×10^3mm^2/s,恶性组ADC值为（1．37±0．75）×10^-3mm^2/s,正常组ADC值为（0．36±0．21）×10^-3mm^2／s,成像条件相同时,良性组高于恶性组,两组间有明显的统计学意义（P〈0．05）。结论：DWI可较好的反映椎体的弥散特征,ADC值作为量化指标可对良恶性椎体压缩性骨折进行可靠鉴别。     

Amide proton exchange measurements as a probe of the stability and dynamics of the N-terminal domain of the ribosomal protein L9: comparison with the intact protein.

Amide H/D exchange rates have been measured for the N-terminal domain of the ribosomal protein L9, residues 1-56. The rates were measured at pD 3.91, 5.03, and 5.37. At pD 5.37, 18 amides exchange slowly enough to give reliable rate measurements. At pD 3.91, seven additional residues could be followed. The exchange is shown to occur by the EX2 mechanism for all conditions studied. The rates for the N-terminal domain are very similar to those previously measured for the corresponding region in the full-length protein (Lillemoen J et al., 1997, J Mol Biol 268:482-493). In particular, the rates for the residues that we have shown to exchange via global unfolding in the N-terminal domain agree within the experimental error with the rates measured by Hoffman and coworkers, suggesting that the structure of the domain is preserved in isolation and that the stability of the isolated domain is comparable to the stability of this domain in intact L9.     

Supertertiary Structure of the MAGUK Core from PSD-95

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Highlights? Using NMR and SAXS, we depict the dynamic structure of the MAGUK core PSD-95 ? PDZ3 of the MAGUK core interacts with SH3 via its canonical peptide binding groove ? Binding of PDZ peptides, such as CRIPT, disrupts the interaction between PDZ3 and SH3 ? Rosetta modeling shows that linker residues L411/M412 dock into the PDZ3 binding site     

Haemosporidian Parasites of Antelopes and Other Vertebrates from Gabon,Central Africa

Re-examination, using molecular tools, of the diversity of haemosporidian parasites (among which the agents of human malaria are the best known) has generally led to rearrangements of traditional classifications. In this study, we explored the diversity of haemosporidian parasites infecting vertebrate species (particularly mammals, birds and reptiles) living in the forests of Gabon (Central Africa), by analyzing a collection of 492 bushmeat samples. We found that samples from five mammalian species (four duiker and one pangolin species), one bird and one turtle species were infected by haemosporidian parasites. In duikers (from which most of the infected specimens were obtained), we demonstrated the existence of at least two distinct parasite lineages related to Polychromophilus species (i.e., bat haemosporidian parasites) and to sauropsid Plasmodium (from birds and lizards). Molecular screening of sylvatic mosquitoes captured during a longitudinal survey revealed the presence of these haemosporidian parasite lineages also in several Anopheles species, suggesting a potential role in their transmission. Our results show that, differently from what was previously thought, several independent clades of haemosporidian parasites (family Plasmodiidae) infect mammals and are transmitted by anopheline mosquitoes.     

A Model of the Quaternary Structure of Enolases, Based on Structural and Evolutionary Analysis of the Octameric Enolase from Bacillus subtilis

Purified enolase from Bacillus subtilis has a native mass of approximately 370 kDa. Since B. subtilis enolase was found to have a subunit mass of 46.58 kDa, the quaternary structure of B. subtilis is octameric. The pl for B. subtilis enolase is 6.1, the pH optimum (pH_o) for activity is 8.1–8.2, and the K _m for 2-PGA is approximately 0.67 mM. Using the dimeric Cα structure of yeast dimeric enolase as a guide, these dimers were arranged as a tetramer of dimers to simulate the electron microscopy image processing obtained for the octameric enolase purified from Thermotoga maritima. This arrangement allowed identification of helix J of one dimer (residues 86–96) and the loop between helix L and strand 1 (HL–S1 loop) of another dimer as possible subunit interaction regions. Alignment of available enolase amino acid sequences revealed that in 16 there are two tandem glycines at the C-terminal end of helix L and the HL–S1 loop is truncated by 4–6 residues relative to the yeast polypeptide, two structural features absent in enolases known to be dimers. From these arrangements and alignments it is proposed that the GG tandem at the C-terminal end of helix L and truncation of the HL–S1 loop may play a critical role in octamer formation of enolases. Interestingly, the sequence features associated with dimeric quaternary structure are found in three phylogenetically disparate groups, suggesting that the ancestral enolase was an octamer and that the dimeric structure has arisen independently multiple times through evolutionary history.