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The elongated antennae decorating eukaryotic glycans are built from polylactosamine repeats. Polylactosamine forms a lectin recognition site and also acts as a platform for presenting diverse additional modifications (e.g., terminal cell-surface antigens); it therefore plays important roles in cell adherence, development, and immunity. Two new papers present a detailed structural and mechanistic investigation of β1-3-Nacetylgucosaminyltransferase 2, a key enzyme in antennae synthesis. The resulting insights will also help decipher other members of GT31, the single largest human glycosyltransferase family. [ABSTRACT FROM AUTHOR]

Ki67 is a protein widely used as cell-proliferation marker, with its cellular functions being hardly unveiled. In this paper, we present the direct interaction between Ki67 and PP1γ, a protein phosphatase showing characteristic accumulation on anaphase chromosomes via the canonical PP1-binding motif within Ki67. In cells depleted of Ki67, PP1γ is targeted to anaphase chromosomes less efficiently. Additionally, overexpression of Ki67, but not a mutant form without the ability to bind PP1γ, induced ectopic localization of PP1γ on metaphase chromosomes. These observations demonstrate that Ki67 is one factor that defines the cellular behavior of PP1γ in anaphase. To explore the specific roles of the subset of PP1γ recruited on chromosome via its interaction with Ki67 (PP1γ-Ki67), endogenous Ki67 was replaced with a Ki67 mutant deficient in its ability to interact with PP1γ. Although no obvious defects in the progression of mitosis were observed, the timing of dephosphorylation of the mutant Ki67 in anaphase was delayed, indicating that Ki67 itself is one of the substrates of PP1γ-Ki67. [ABSTRACT FROM AUTHOR]

Nonspecific cross-reacting antigen-2 (NCA-2) is a glycoprotein purified from meconium as a closely correlated entity with carcinoembryonic antigen (CEA). As in the case of CEA, only asparagine-linked sugar chains are included in NCA-2. In order to elucidate the structural characteristics of the sugar chains of NCA-2, they were quantitatively released from the polypeptide backbone by hydrazinolysis and reduced with NaB3H4 after N-acetylation. The radioactive oligosaccharides were fractionated by paper electrophoresis, serial chromatography on immobilized lectin columns, and Bio-Gel P-4 (under 400 mesh) column chromatography. Structures of the oligosaccharides were estimated from the data of the binding specificities of immobilized lectin columns and the effective size of each oligosaccharide determined by passing through a Bio-Gel P-4 column and were then confirmed by endo-beta-galactosidase digestion, sequential digestion with exoglycosidases with different aglycon specificities, and methylation analysis. NCA-2 contains a similar number (27 mol) of sugar chains in one molecule compared with CEA (24-26 mol). However, all sugar chains of NCA-2 were complex-type in contrast to CEA, approximately 8% of the sugar chains of which were high mannose-type (Yamashita, K., Totani, K., Kuroki, M., Matsuoka, Y., Ueda, I., and Kobata, A. (1987) Cancer Res. 47, 3451-3459). About 80% of the oligosaccharides from NCA-2 contain bisecting N-acetylglucosamine residues, and the percent molar ratio of mono-, bi, tri, and tetraantennary oligosaccharides was 2:14:57:27. (+/- Fuc alpha 1----2)Gal beta 1----4(+/- Fuc alpha 1----3)GlcNAc, (+/- Fuc alpha 1----2)Gal beta 1----3(+/- Fuc alpha 1----4)GlcNAc, (+/- Fuc alpha 1----2)Gal beta 1----4(+/- Fuc alpha 1----3)GlcNAc beta 1---- 3Gal beta 1----4GlcNAc, (+/- Fuc alpha 1----2)Gal beta 1----3(+/- Fuc alpha 1----4)GlcNAc beta 1---- 3Gal beta 1----4GlcNAc, and GalNAc beta 1----3Gal beta 1----3GlcNAc beta 1----3Gal beta 1----4GlcNAc were found as their outer chain moieties. Approximately 60% of the oligosaccharides from NCA-2 contain the Gal beta 1----4 or 3GlcNAc beta 1----3Gal beta 1----4GlcNAc beta 1----group in their outer chains.

Although essential for T cell function, the identity of the T cell receptor (TCR) "inside-out" pathway for the activation of lymphocyte function-associated antigen 1 (LFA-1) is unclear. SKAP1 (SKAP-55) is the upstream regulator needed for TCR-induced RapL-Rap1 complex formation and LFA-1 activation. In this paper, we show that SKAP1 is needed for RapL binding to membranes in a manner dependent on the PH domain of SKAP1 and the PI3K pathway. A SKAP1 PH domain-inactivating mutation (i.e. R131M) markedly impaired RapL translocation to membranes for Rap1 and LFA-1 binding and the up-regulation of LFA-1-intercellular adhesion molecule 1 (ICAM-1) binding. Further, N-terminal myr-tagged SKAP1 for membrane binding facilitated constitutive RapL membrane and Rap1 binding and effectively substituted for PI3K and TCR ligation in the activation of LFA-1 in T cells. [ABSTRACT FROM AUTHOR]

Myelin basic protein is a candidate autoantigen in multiple sclerosis. One of its dominant antigenic epitopes is segment Pro85 to Pro96 (human sequence numbering, corresponding to Pro82 to Pro93 in the mouse). There have been several, contradictory predictions of secondary structure in this region; either β-sheet, α-helix, random coil, or combinations thereof have all been proposed. In this paper, molecular dynamics and site-directed spin labeling in aqueous solution indicate that this segment forms a transient α-helix, which is stabilized in 30% trifluoroethanol. When bound to a myelin-like membrane surface, this antigenic segment exhibits a depth profile that is characteristic of an amphipathic α-helix, penetrating up to 12 Å into the bilayer. The α-helix is tilted ∼9°, and the central lysine is in an ideal snorkeling position for side-chain interaction with the negatively charged phospholipid head groups. [ABSTRACT FROM AUTHOR]