Psoriasin (S100A7) associates with integrin ß6 subunit and is required for αvß6-dependent carcinoma cell invasion.

Expression of the integrin αvß6 is upregulated in a variety of carcinomas where it appears to be involved in malignant progression, although the biology of this integrin is not fully explored. We have generated oral carcinoma cells that express αvß6 composed of wild-type αv and a mutant ß6 that lacks the unique C-terminal 11 amino acids (aa). We found that these residues, although not required for αvß6-dependent adhesion or migration, are essential for αvß6-dependent invasive activity. We have used a proteomic approach to identify novel binding partners for the ß6 subunit cytoplasmic tail and report that psoriasin (Psor) (S100A7) bound preferentially to the recombinant ß6 cytoplasmic domain, though not in the absence of the unique C-terminal 11aa. Endogenous cellular Psor co-precipitated with endogenous ß6 and colocalised with αvß6 at the cell membrane and intracellular vesicles. Knockdown of Psor, with small interfering RNA, had no effect on αvß6-dependent adhesion or migration but abrogated αvß6-mediated oral carcinoma cell invasion both in Transwell and, the more physiologically relevant, organotypic invasion assays, recapitulating the behaviour of the ß6-mutant cell line. Membrane-permeant Tat-peptides encoding the unique C-terminal residues of ß6, bound directly to recombinant Psor and inhibited cellular Psor binding to ß6; this blocked αvß6-dependent, but not αvß6-independent, invasion. These data identify a novel interaction between Psor and ß6 and demonstrate that it is required for αvß6-dependent invasion by carcinoma cells. Inhibition of this interaction may represent a novel therapeutic strategy to target carcinoma invasion.

Alternate substrate binding modes to two mutant (D98N and H255N) forms of nitrite reductase from Alcaligenes faecalis S-6: structural model of a transient catalytic intermediate.

High-resolution nitrite soaked oxidized and reduced crystal structures of two active site mutants, D98N and H255N, of nitrite reductase (NIR) from Alcaligenes faecalis S-6 were determined to better than 2.0 A resolution. In the oxidized D98N nitrite-soaked structures, nitrite is coordinated to the type II copper via its oxygen atoms in an asymmetric bidentate manner; however, elevated B-factors and weak electron density indicate that both nitrite and Asn98 are less ordered than in the native enzyme. This disorder likely results from the inability of the N delta 2 atom of Asn98 to form a hydrogen bond with the bound protonated nitrite, indicating that the hydrogen bond between Asp98 and nitrite in the native NIR structure is essential in anchoring nitrite in the active site for catalysis. In the oxidized nitrite soaked H255N crystal structure, nitrite does not displace the ligand water and is instead coordinated in an alternative mode via a single oxygen to the type II copper. His255 is clearly essential in defining the nitrite binding site despite the lack of direct interaction with the substrate in the native enzyme. The resulting pentacoordinate copper site in the H255N structure also serves as a model for a proposed transient intermediate in the catalytic mechanism consisting of a hydroxyl and nitric oxide molecule coordinated to the copper. The formation of an unusual dinuclear type I copper site in the reduced nitrite soaked D98N and H255N crystal structures may represent an evolutionary link between the mononuclear type I copper centers and dinuclear Cu(A) sites.

Catalytic roles for two water bridged residues (Asp-98 and His-255) in the active site of copper-containing nitrite reductase.

Two active site residues, Asp-98 and His-255, of copper-containing nitrite reductase (NIR) from Alcaligenes faecalis have been mutated to probe the catalytic mechanism. Three mutations at these two sites (D98N, H255D, and H255N) result in large reductions in activity relative to native NIR, suggesting that both residues are involved intimately in the reaction mechanism. Crystal structures of these mutants have been determined using data collected to better than 1. 9-A resolution. In the native structure, His-255 Nepsilon2 forms a hydrogen bond through a bridging water molecule to the side chain of Asp-98, which also forms a hydrogen bond to a water or nitrite oxygen ligated to the active site copper. In the D98N mutant, reorientation of the Asn-98 side chain results in the loss of the hydrogen bond to the copper ligand water, consistent with a negatively charged Asp-98 directing the binding and protonation of nitrite in the native enzyme. An additional solvent molecule is situated between residues 255 and the bridging water in the H255N and H255D mutants and likely inhibits nitrite binding. The interaction of His-255 with the bridging water appears to be necessary for catalysis and may donate a proton to reaction intermediates in addition to Asp-98.

Occurrence of homologs of the Escherichia coli lytB gene in gram-negative bacterial species.

The Escherichia coli LytB protein regulates the activity of guanosine 3',5'-bispyrophosphate synthetase I (RelA). A Southern blot analysis of chromosomal DNA with the E. coli lytB gene as a probe revealed the presence of lytB homologs in all of the gram-negative bacterial species examined but not in gram-positive species. The lytB homologs from Enterobacter aerogenes and Pseudomonas fluorescens complemented the E. coli lytB44 mutant allele.

Human plasma fibronectin effect on serum-mediated uptake of Pseudomonas aeruginosa PA 1348A by human granulocytes.

The effect of human plasma fibronectin on human granulocyte (PMN) phagocytosis of one strain of Pseudomonas aeruginosa (PA 1348A) was examined in a previously defined optimal phagocytic assay. Normal and fibronectin-deficient serum demonstrated similar rates of bacterial uptake by PMNs. Complement depletion of both sera inhibited phagocytosis. Addition of purified fibronectin did not alter phagocytosis. These findings strongly support the conclusion that fibronectin neither promotes nor inhibits opsonization for phagocytosis of this strain of P. aeruginosa.