Proteolysis in protein import and export: Signal peptide processing in eu-and prokaryotes

Numerous proteins in pro-and eukaryotes must cross cellular membranes in order to reach their site of function. Many of these proteins carry signal sequences that are removed by specific signal peptidases during, or shortly after, membrane transport. Signal peptidases have been identified in the rough endoplasmic reticulum, the matrix and inner membrane of mitochondria, the stroma and thylakoid membrane of chloroplasts, the bacterial plasma membrane and the thylakoid membrane of cyanobacteria. The composition of these peptidases varies between one and several subunits. No site-specific inhibitors are known for the majority of these enzymes. Accordingly, signal peptidases recognize structural motifs rather than linear amino acid sequences. Such motifs have become evident by employing extensive site-directed mutagenesis to investigate the anatomy of signal sequences. Analysis of the reaction specificities and the primary sequences of several signal peptidases suggests that the enzymes of the endoplasmic reticulum, the inner mitochondrial membrane and the thylakoid membrane of chloroplasts all have evolved from bacterial progenitors.     

牛乳蛋白在人工瘤胃和小肠液中体外降解的动态变化

研究了牛乳蛋白在人工瘤胃和小肠液中体外消化的动态过程.采用高效液相色谱分析消化液中的游离氨基酸含量,同时测定消化液中蛋白浓度和组成的变化.结果显示,脱脂乳在人工瘤胃中发酵24 h内,总游离氨基酸含量逐渐增加,其中Arg、Leu和Pro含量增加最明显;发酵30 min~7 h内,蛋白浓度迅速下降;发酵5 h后,大部分酪蛋白被降解,而β-乳球蛋白和α-乳清蛋白变化很小;脱脂乳在小肠液中进行体外消化,总游离氨基酸迅速增加,反应至7 h时,溶液中的总游离氨基酸增加约4倍,其中以Arg、Tyr、Phe、Leu、Lys和Pro含量增加最明显.     

白蛋白在毛细血管壁内的扩散、吸附和渗流作用

建立白蛋白在毛细血管壁孔隙中运动的物理模型，并对白蛋白在毛细血管壁孔隙中的吸附、扩散及渗透作用进行数值求解．计算结果表明，扩散使白蛋白在毛细血管壁孔隙中的浓度下降，吸附使白蛋白损耗，导致浓度传播滞后，根据白蛋白在毛细血管壁孔隙中的吸附、扩散及渗透作用，提出了“胶体蛋白墙”的概念及理论，并解释了水肿的形成机理。     

Depletion of phosphatidylglycerol head-group induces changes in oxygen evolution and protein secondary structures of photosystemⅡ

The techniques of oxygen electrode polarography and Fourier transform infrared (FT-IR) spectroscopy were employed to explore the roles of polar head-group of phosphatidylglycerol (PG) molecules in the functional and structural aspects of photosystemⅡ(PSⅡ) through enzymatic approach. It was shown that the depletion of PG by treatment of phospholipase C (PLC) on PSⅡ particles caused the inhibition of oxygen evolving activity in PSⅡ. This effect also gave rise to changes in the protein secondary structures of PSⅡ, that is, an increase in α-helical conformation which is compensated by the loss of β-strand structures. It revealed that the head-group of PG molecules plays an important structural role in the maintenance of normal structure of PSⅡ proteins, which is required to maintain the appropriate physiological activity of the PSⅡ complex such as the oxygen evolving activity. It is suggested that there most probably exist hydrogen-bonding interactions between PG molecules and PSⅡ proteins.     

Protein kinase TTK interacts and co-localizes with CENP-E to the kinetochore of human cells

Spindle checkpoint is an important biochemical signaling cascade during mitosis which monitors the fidelity of chromosome segregation, and is mediated by protein kinases Mps1 and Bub1/BubR1. Our recent studies show that kinesin-related motor protein CENP-E interacts with BubR1 and participates in spindle checkpoint signaling. To elucidate the molecular mechanisms underlying spindle checkpoint signaling, we carried out proteomic dissection of human cell kinetochore and revealed protein kinase TTK, human homologue of yeast Mps1. Our studies show that TTK is localized to the kinetochore of human cells, and interacts with CENP-E, suggesting that TTK may play an important role in chromosome segregation during mitosis.     

去除后肢神经支配对大鼠骨骼肌中钠钾腺苷酶各亚基表达的影响

检测了去除神经支配的大鼠后肢和对侧的对照后肢骨骼肌中钠钾腺苷酶(Na—K—ATPase)各亚基的蛋白质和mRNA的表达，结果表明，去除后肢神经支配4d，在红色骨骼肌中α2和β1亚基的蛋白质表达显著下降(分别下降了46％和77％)，在红色腓肠肌和比目鱼肌中，α2亚基的mRNA水平分别下降了29％和39％，β1亚基的mRNA水平分别下降了80％和52％，在白色骨骼肌中α2亚基的蛋白质和mRNA水平无显著变化；在红色和白色骨骼肌中，α1亚基的蛋白质表达分别增加了20％和15％，同时伴随着更大幅度的mRNA水平的增加，而β2亚基的蛋白质表达未发生显著变化，其mRNA水平在红色腓肠肌中也无显著变化，但在白色腓肠肌中减少了59％．这些结果证实，在去除神经支配的大鼠骨骼肌中，钠钾腺苷酶各亚基的表达受转录和转录后调控，与已报道的胰岛素特异性诱导α2和β1亚基向细胞膜转移的研究结果相吻合．实验中仅α2和β1亚基的蛋白质表达显著下降暗示，在大鼠骨骼肌中，由于去除神经支配造成的胰岛素抵抗使原本受胰岛素调节的钠钾腺苷酶亚基的表达机制受到破坏．