Peptide selection by class I molecules of the major histocompatibility complex

Class I molecules of the major histocompatibility complex (MHC) bind peptides derived from cytoplasmic proteins. Comparison of over 100 such peptides reveals the importance of the carboxy-terminal residue in selective binding. Recent evidence implicates the proteases and transporters of the processing pathway in providing peptides with the correct residues at the carboxyl terminus.     

大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育

本实验用免疫组织化学ＡＢＣ法研究了大鼠胼胝体内神经肽Ｙ免疫反应阳性（ＮＰＹ－ＩＲ）纤维的生后发育。结果发现,许多ＮＰＹ－ＩＲ纤维在大鼠出生时便存在于胼胝体内。ＮＰＹ－ＩＲ胼胝体纤维的密度在生后１周内继续逐渐增高,在第２周内达到最高峰。之后,ＮＰＹ－ＩＲ胼胝体纤维的密度逐渐下降,至第３周末时接近成年时的水平,即仅有少量ＮＰＹ－ＩＲ纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多ＮＰＹ－ＩＲ胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。     

Phosphorylation of serine-15 of maize leaf sucrose synthase. Occurrence in vivo and possible regulatory significance.

Experiments were conducted to determine whether sucrose synthase (SuSy) was phosphorylated in the elongation zone of maize (Zea mays L.) leaves. The approximately 90-kD subunit of SuSy was 32P-labeled on seryl residue(s) when excised shoots were fed [32P]orthophosphate. Both isoforms of SuSy (the SS1 and SS2 proteins) were phosphorylated in vivo, and tryptic peptide-mapping analysis suggested a single, similar phosphorylation site in both proteins. A combination of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and automated Edman sequencing analysis unequivocally identified the phosphorylation site in the maize SS2 protein as serine-15. This site was phosphorylated in vitro by endogenous protein kinase(s) in a strictly Ca(2+)-dependent manner. A synthetic peptide, based on the phosphorylation site sequence, was used to identify and partially purify an endogenous Ca(2+)-dependent protein kinase(s) from the maize leaf elongation zone and expanding spinach leaves. Phosphorylation of SuSy in vitro selectively activates the cleavage reaction by increasing the apparent affinity of the enzyme for sucrose and UDP, suggesting that phosphorylation may be of regulatory significance. Conservation of the phosphorylation site, and the sequences surrounding it, among plant species suggests that phosphorylation of SuSy may be widespread, if not universal, in plants.