BPAG1 is the major antigenic determinant of autoimmune sera of bullous pemphigoid (BP) patients. It is made by stratified squamous epithelia, where it localizes to the inner surface of specialized integrin-mediated adherens junctions (hemidesmosomes). To explore the function of BPAG1 and its relation to BP, we targeted the removal of the BPAG1 gene in mice. Hemidesmosomes are otherwise normal, but they lack the inner plate and have no cytoskeleton attached. Though not affecting cell growth or substratum adhesion, this compromises mechanical integrity and influences migration. Unexpectedly, the mice also develop severe dystonia and sensory nerve degeneration typical of dystonia musculorum (dt/dt) mice. We show that in at least one other strain of dt/dt mice, BPAG1 gene is defective.

Photoactive yellow protein (PYP) is a member of the xanthopsin family of eubacterial blue-light photoreceptors. On absorption of light, PYP enters a photocycle that ultimately transduces the energy contained in a light signal into an altered biological response. Nanosecond time-resolved x-ray crystallography was used to determine the structure of the short-lived, red-shifted, intermediate state denoted [pR], which develops within 1 nanosecond after photoelectronic excitation of the chromophore of PYP by absorption of light. The resulting structural model demonstrates that the [pR] state possesses the cis conformation of the 4-hydroxyl cinnamic thioester chromophore, and that the process of trans to cis isomerization is accompanied by the specific formation of new hydrogen bonds that replace those broken upon excitation of the chromophore. Regions of flexibility that compose the chromophore-binding pocket serve to lower the activation energy barrier between the dark state, denoted pG, and [pR], and help initiate entrance into the photocycle. Direct structural evidence is provided for the initial processes of transduction of light energy, which ultimately translate into a physiological signal.

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...

Neuropilin-1 (Npn-1) is a receptor for both semaphorin 3A (Sema3A) and vascular endothelial growth factor 165 (VEGF 165 ). To understand the role Npn-1 plays as a receptor for these structurally and functionally unrelated ligands, we set out to identify structural features of Npn-1 that confer binding to Sema3A or VEGF 165 . We constructed Npn-1 variants containing deletions within the "a" A complex but ordered series of axon guidance decisions during development is critical for the establishment of nervous system structure and function (1). The vertebrate vascular network is similarly complex, with interconnecting conduits that extend throughout the body that are often in close anatomical proximity to nerve pathways (2). Recent evidence suggests that at least some of the same ligand-receptor systems coordinate development of both the nervous system and the cardiovascular system. For example, Eph receptors and their ligands, the ephrins, were first characterized as mediators of repulsive guidance events crucial for correct navigation of neuronal growth cones and migrating neural crest cells (3, 4). Their unexpected role in blood vessel formation was revealed when mutant mice that lacked either ephrin B2 or its cognate receptor EphB4 were shown to die during embryogenesis due to cardiovascular dysfunction (5, 6). Consistent with this observation, ephrin B2 and EphB4 were shown to have a reciprocal expression patterns in arterial and venous endothelial cells (6).Another example of a cell surface receptor whose function is required for development of both the cardiovascular and nervous systems is neuropilin-1 (Npn-1).

The photocycle of the bacterial blue-light photoreceptor, photoactive yellow protein, was stimulated by illumination of single crystals by a 7 ns laser pulse. The molecular events were recorded at high resolution by time-resolved X-ray Laue diffraction as they evolved in real time, from 1 ns to seconds after the laser pulse. The complex structural changes during the photocycle at ambient temperature are displayed in a movie of difference electron density maps relative to the dark state. The step critical to entry into the photocycle is identified as flipping of the carbonyl group of the 4-hydroxycinnamic acid chromophore into an adjacent, hydrophobic environment rather than the concomitant isomerization about the double bond of the chromophore tail. The structural perturbation generated at the chromophore propagates throughout the entire protein as a light-induced "protein quake" with its "epicenter" at the carbonyl moiety of the chromophore.

The Eap (extracellular adherence protein) of Staphylococcus aureus functions as a secreted virulence factor by mediating interactions between the bacterial cell surface and several extracellular host proteins. Eap proteins from different Staphylococcal strains consist of four to six tandem repeats of a structurally uncharacterized domain (EAP domain). We have determined the three-dimensional structures of three different EAP domains to 1.8, 2.2, and 1.35 Å resolution, respectively. These structures reveal a core fold that is comprised of an ␣-helix lying diagonally across a five-stranded, mixed ␤-sheet. Staphylococcus aureus is a widespread, persistent pathogen that causes a broad range of diseases in humans and animals, from simple wound infections to more severe conditions such as septicemia, endocarditis, and osteomyelitis (2). As is the case with many pathogens, initiation of S. aureus infection requires colonization of unique microenvironments within the host. To facilitate host colonization, S. aureus expresses a diverse array of virulence-determining factors, including exoenzymes, toxins, and numerous protein adhesins. These adhesins (termed Receptins (3, 4) or MSCRAMMs (4) (for microbial surface compo-

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Wavelength normalization is an essential part of processing of Laue X-ray diffraction data and is critically important for deriving accurate structure-factor amplitudes. The results of wavelength normalization for Laue data obtained in nanosecond time-resolved experiments at the ID09 beamline at the European Synchrotron Radiation Facility, Grenoble, France, are presented. Several wiggler and undulator insertion devices with complex spectra were used. The results show that even in the most challenging cases, such as wiggler/undulator tandems or single-line undulators, accurate wavelength normalization does not require unusually redundant Laue data and can be accomplished using typical Laue data sets. Single-line undulator spectra derived from Laue data compare well with the measured incident X-ray spectra. Successful wavelength normalization of the undulator data was also confirmed by the observed signal in nanosecond time-resolved experiments. Single-line undulators, which are attractive for time-resolved experiments due to their high peak intensity and low polychromatic background, are compared with wigglers, based on data obtained on the same crystal.