We present a model of opinion dynamics in which agents adjust continuous opinions as a result of random binary encounters whenever their difference in opinion is below a given threshold. High thresholds yield convergence of opinions towards an average opinion, whereas low thresholds result in several opinion clusters: members of the same cluster share the same opinion but are no longer influenced by members of other clusters.

The synthesis of both pro-inflammatory leukotrienes and anti-inflammatory lipoxins requires the enzyme 5-lipoxygenase (5-LOX). 5-LOX activity is short-lived, apparently in part due to an intrinsic instability of the enzyme. We identified a 5-LOX-specific destabilizing sequence that is involved in orienting the carboxy-terminus which binds the catalytic iron. Herein we report the crystal structure at 2.4 Å resolution of human 5-LOX stabilized by replacement of this sequence.

Neuropilin (Nrp) is a cell surface receptor with essential roles in angiogenesis and axon guidance. Interactions between Nrp and the positively charged C termini of its ligands, VEGF and semaphorin, are mediated by Nrp domains b1 and b2, which share homology to coagulation factor domains. We report here the crystal structure of the tandem b1 and b2 domains of Nrp-1 (N1b1b2) and show that they form a single structural unit. Cocrystallization of N1b1b2 with Tuftsin, a peptide mimic of the VEGF C terminus, reveals the site of interaction with the basic tail of VEGF on the b1 domain. We also show that heparin promotes N1b1b2 dimerization and map the heparin binding site on N1b1b2. These results provide a detailed picture of interactions at the core of the Nrp signaling complex and establish a molecular basis for the synergistic effects of heparin on Nrp-mediated signaling.semaphorin ͉ Tuftsin ͉ VEGF N europilins (Nrps) are essential cell surface receptors with central roles in both angiogenesis and axon guidance (1-3). During angiogenesis, Nrp directly binds VEGF and functions as a coreceptor for VEGF along with VEGF receptor (VEGFR)-2, one of the three VEGFR tyrosine kinases (3, 4). During neural development, Nrp directly binds semaphorin and functions as a semaphorin coreceptor with members of the plexin family (5). Additionally, interactions with both neural adhesion protein L1 and Nrp-interacting protein (NIP), have been shown to be involved in a variety of other cellular processes (6-8).Nrp plays a stimulatory role in angiogenesis, a process critical for growth of solid tumors (reviewed in refs. 4 and 9-11). Nrp expression is observed in tumor vasculature, and overexpression promotes tumorigenesis in vivo for a variety of solid tumors including pituitary, prostate, breast, and colon cancers (12-15). In contrast, a soluble splice form containing only part of the extracellular domain of Nrp inhibits tumorigenesis (16) as do a number of peptides that block VEGF binding to Nrp (17,18). Recent evidence has also demonstrated a role for Nrp in hematological malignancies. Nrp overexpression is observed in both multiple myeloma and acute myeloid leukemia and, in the latter case, is associated with significantly reduced survival (19,20). Strategies to inhibit Nrp activity are thus being developed as potential antitumor therapies (reviewed in ref. 11).Higher eukaryotes possess two Nrp homologs, Nrp-1 and Nrp-2, which share 44% amino acid sequence identity (1). Nrp extracellular regions are composed of two complement binding CUB domains (a1 and a2) followed by two coagulation factor domains (b1 and b2), a MAM (meprin, A5, ) domain (c1), a single membrane-spanning region, and a short cytoplasmic tail (Fig. 1A) (21, 22). The a1 and a2 domains of Nrp are essential for binding to the core seven-bladed Sema domain of semaphorin as well as contributing to interactions with VEGF (23, 24). The coagulation factor domains b1 and b2 contain the high-affinity binding site for the basic heparin binding domain (HBD) of VEGF165 as well a...