Stenotrophomonas maltophilia is increasingly emerging as a multiresistant pathogen in the hospital environment. In immunosuppressed patients, these bacteria may cause severe infections associated with tissue lesions such as pulmonary hemorrhage. This suggests proteolysis as a possible pathogenic mechanism in these infections. This study describes a protease with broad specificity secreted by S. maltophilia. The gene, termed StmPr1, codes for a 63-kDa precursor that is processed to the mature protein of 47 kDa. The enzyme is an alkaline serine protease that, by sequence homology and enzymic properties, can be further classified as a new member of the family of subtilases. It differs from the classic subtilisins in molecular size, in substrate specificity, and probably in the architecture of the active site. The StmPr1 protease is able to degrade several human proteins from serum and connective tissue. Furthermore, pan-protease inhibitors such as ␣ 1 -antitrypsin and ␣ 2 -macroglobulin were unable to abolish the activity of the bacterial protease. The data support the interpretation that the extracellular protease of S. maltophilia functions as a pathogenic factor and thus could serve as a target for the development of therapeutic agents.Stenotrophomonas maltophilia, formerly referred to as Xanthomonas maltophilia or Pseudomonas maltophilia (1, 2), is an aerobic nonfermentative Gram-negative bacterium of widespread occurrence. For healthy humans, it is regarded as an opportunistic germ; it has been implicated in a variety of infections without distinctive clinical features (for a review, see Ref.3). However, in immune-compromised patients, particularly those with bone marrow aplasia or receiving intensive chemotherapy, cases of fulminant hemorrhagic pneumonia have been reported, even with fatal outcome (4 -6). In patients not surviving infections with S. maltophilia, histological inspection of the lung tissue revealed massive bleeding caused by damage to the lung epithelium (4). There are further reports demonstrating involvement of this bacterium in massive hemorrhagic processes of the small intestine and the subclavian artery accompanied by severe lesions of the tissue (5, 6). These observations strongly suggest the participation of proteolytic activity, produced by the bacteria, which may damage the infected tissue. Indeed, it is known that members of the Pseudomonaceae express and secrete a variety of proteases (cf. Ref. 7). Whereas the primary function of these enzymes is to provide a source of free amino acids for bacterial survival and growth, there is accumulating evidence that bacterial proteases may play a pathogenic role in the infected host by involvement in tissue invasion and destruction, evasion of host defenses, and modulation of the host immune system (8).The broad administration of antibiotics currently applied in cases of intensive care patients leads to selection of multiresistant S. maltophilia strains. Consequently, these bacteria are found with increasing frequency in the hospital environmen...

The insulin receptor substrate of 53 kDa (IRSp53) is a target of the small GTPase cdc42 which is strongly enriched in the postsynaptic density of excitatory synapses. IRSp53 interacts with the postsynaptic shank1 scaffolding molecule in a cdc42 regulated manner. The functional significance of the cdc42/ IRSp53 pathway in postsynaptic sites is however, unclear. The generation of excitatory synapses in the central nervous system requires a complex assembly process in which elements of the postsynaptic receptor apparatus are assembled at postsynaptic sites on dendrites. In many cases, glutamatergic synapses are localized on the heads of dendritic spines (Harris and Kater 1994; see review by Hering and Sheng 2001). During maturation postsynaptic proteins accumulate at the synapse, as exemplified in several studies by the appearance of clusters of the postsynaptic marker PSD-95 (Friedman et al. 2000;Okabe et al. 2001). Via its PDZ domains, PSD-95 is one of the major anchoring proteins for postsynaptic transmitter receptors and ion channels (Kim et al. 1995;Kornau et al. 1995). Through an intricate network of protein interactions, a large protein complex of up to 100 proteins is assembled at the spine heads around the PSD-95/transmitter receptor complex (Husi et al. 2000;Walikonis et al. 2000;Li et al. 2004) which has been termed the postsynaptic density (PSD). The function of the PSD appears to be to physically link postsynaptic receptors to signalling molecules, and to provide stable attachment of the receptors to the actin-based cytoskeleton of the dendritic spine. Shank proteins (shank1-3, also known as SSTRIP, ProSAP, synamon or CortBP) constitute another group of postsynaptic scaffolding molecules which link transmitter receptors (Kreienkamp et al. 2000;Naisbitt et al. 1999;Yao et al. 1999;Zitzer et al. 1999) to actin binding proteins (Du et al. 1998;Boeckers et al. 2001;Okamoto et al. 2001). Overexpression of shank1 in neurones leads to enhanced maturation of dendritic spines . We and others have recently identified IRSp53 as an interaction partner for shank1 (Bockman et al. 2002;Soltau et al. 2002). A proline-rich region of shank1 binds to the SH3 domain of IRSp53 in a cdc42-regulated manner (Soltau et al. 2002). These data suggested that shank1 might be an effector molecule of cdc42 in an undefined regulatory pathway. Here, we show that IRSp53, via binding to a PDZ domain of the PSD-95 molecule, mediates the formation of a triple complex consisting of shank1 and PSD-95. Our data suggest that one result of cdc42/IRSp53 signalling is the regulated assembly of a macromolecular complex between shank and PSD-95 proteins.Received January 14, 2004; revised manuscript received March 19, 2004; accepted March 23, 2004. Address correspondence and reprint requests to Hans-Jürgen Kreienkamp, Institut für Zellbiochemie und klinische Neurobiologie, Universitätsklinikum Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany. E-mail: kreienkamp@uke.uni-hamburg.deAbbreviations used: IRSp53, insulin receptor su...

Chicken acidic leucine-rich EGF-like domain containing brain protein (CALEB) was identified by combining binding assays with immunological screens in the chicken nervous system as a novel member of the EGF family of differentiation factors. cDNA cloning indicates that CALEB is a multidomain protein that consists of an NH2-terminal glycosylation region, a leucine-proline–rich segment, an acidic box, a single EGF-like domain, a transmembrane, and a short cytoplasmic stretch. In the developing nervous system, CALEB is associated with glial and neuronal surfaces. CALEB is composed of a 140/130-kD doublet, an 80-kD band, and a chondroitinsulfate-containing 200-kD component. The latter two components are expressed in the embryonic nervous system and are downregulated in the adult nervous system. CALEB binds to the extracellular matrix glycoproteins tenascin-C and -R. In vitro antibody perturbation experiments reveal a participation of CALEB in neurite formation in a permissive environment.

Neuroligins are postsynaptic cell adhesion molecules that associate with presynaptic neurexins. Both factors form a transsynaptic connection, mediate signalling across the synapse, specify synaptic functions and play a role in synapse formation. Neuroligin dysfunction impairs synaptic transmission, disrupts neuronal networks and is thought to participate in cognitive diseases. Here we report that chemical treatment designed to induce LTP or LTD induces neuroligin 1/3 turnover, leading to either increased or decreased surface membrane protein levels, respectively. Despite its structural role at a crucial transsynaptic position, GFP-neuroligin 1 leaves synapses in hippocampal neurons over time with chemical LTD-induced neuroligin internalization depending on an intact microtubule cytoskeleton. Accordingly, neuroligin 1 and its binding partner PSD-95 associate with components of the dynein motor complex and undergo retrograde co-transport with a dynein-subunit. Transgenic depletion of dynein function in mice causes postsynaptic NLG1/3 and PSD-95 enrichment. In parallel, postsynaptic density (PSD) lengths and spine head sizes are significantly increased, a similar phenotype as observed upon transgenic overexpression of NLG1 (Dahlhaus et al., 2009). Moreover, application of a competitive PSD-95 peptide or neuroligin 1 C-terminal mutagenesis, specifically alter neuroligin 1 surface membrane expression and interfere with its internalization. Our data suggest the concept that synaptic plasticity regulates neuroligin turnover through active cytoskeleton transport.

The degradation of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) by insulin-degrading enzyme (IDE) has been investigated. As revealed by high-performance liquid chromatography, all three peptides are sequentially cleaved at a limited number of sites, the latter of which were identified by mass spectrometric analyses. The studies revealed that ANP is preferred as substrate over BNP and CNP. ANP degradation is rapidly initiated by hydrolysis at the Ser25-Phe26 bond. Three additional cleavage sites were identified in ANP after prolonged incubation with IDE; in contrast, three and two bonds were hydrolyzed in BNP and CNP, respectively. Analysis of the nine cleavage sites shows a preference for basic or hydrophobic amino acid residues on the carboxyl side of a cleaved peptide bond. In contrast to most of the peptide fragments generated by IDE activity, the initial ANP cleavage product, F-R-Y, is rapidly degraded further by cleavage of the R-Y bond. Cross-linking studies with 125I-ANP in the presence of sulfhydryl-modifying agent indicate that IDE activity is inhibited at the level of initial substrate binding whereas metal-ion chelating agents only prevent hydrolysis. On the basis of its structural and enzymatic properties, IDE exhibits striking similarity to a number of recently-described endopeptidases.