The extracellular functions of galectin-7 (p53-induced gene 1) are largely unknown. On the surface of neuroblastoma cells (SK-N-MC), the increased GM 1 density, a result of upregulated ganglioside sialidase activity, is a key factor for the switch from proliferation to differentiation. We show by solid-phase and cell assays that the sugar chain of this ganglioside is a ligand for galectin-7. In serum-supplemented proliferation assays, galectin-7 reduced neuroblastoma cell growth without the appearance of features characteristic for classical apoptosis. The presence of galectin-3 blocked this effect, which mechanistically resembles that of galectin-1. By virtue of carbohydrate binding, galectin-7 thus exerts neuroblastoma growth control similar to galectin-1 despite their structural differences. In addition to p53-linked proapoptotic activity intracellularly, galectin-7, acting as a lectin on the cell surface, appears to be capable of reducing cancer cell proliferation in susceptible systems.

CD1 proteins present lipid antigens to T cells. The antigens are acquired in the endosomal compartments. This raises the question of how the large hydrophobic CD1 pockets are preserved between the moment of biosynthesis in the endoplasmic reticulum and arrival to the endosomes. To address this issue, the natural ligands associated with a soluble form of human CD1b have been investigated. Using isoelectric focusing, native mass spectrometry and resolving the crystal structure at 1.8 Å resolution, we found that human CD1b is simultaneously associated with endogenous phosphatidylcholine (PC) and a 41-44 carbon atoms-long spacer molecule. The two lipids appear to work in concert to stabilize the CD1b groove, their combined size slightly exceeding the maximal groove capacity. We propose that the spacer serves to prevent binding of ligands with long lipid tails, whereas short-chain lipids might still displace the PC, which is exposed at the groove entrance. The data presented herein explain how the CD1b groove is preserved, and provide a rationale for the in vivo antigen-binding properties of CD1b.

Herein we report the formation and characterization of a novel type of capsules resulting from the self-association between oppositely charged complementary building blocks in MeOH/H2O. The assembly is based on the interaction between tetraamidinium calix[4]arenes 1a-d and tetrasulfonato calix[4]arene 2. Evidence for the formation of the expected 1:1 assemblies is provided by proton NMR, ESI-MS, and ITC. The association process is fast on the NMR time scale and strongly entropy driven, with association constants in the range of 10(6) M-1. The system 1a.2 shows binding affinity toward acetylcholine, tetramethylammonium, and N-methylquinuclidinium cations.