Pore network geometries of intra‐aggregate pore spaces are of great importance for water and ion flux rates controlling C sequestration and bioremediation. Advances in non‐invasive three‐dimensional imaging techniques such as synchrotron‐radiation‐based x‐ray microtomography (SR‐μCT), offer excellent opportunities to study the interrelationships between pore network geometry and physical processes at spatial resolutions of a few micrometers. In this paper we present quantitative three‐dimensional pore‐space geometry analyses of small scale (∼5 mm across) soil aggregates from different soil management systems (conventionally tilled vs. grassland). Reconstructed three‐dimensional microtomography images at approximate isotropic voxel resolutions between 3.2 and 5.4 μm were analyzed for pore‐space morphologies using a suite of image processing algorithms associated with the software published by Lindquist et al. Among the features quantified were pore‐size distributions (PSDs), throat‐area distributions, effective throat/pore radii ratios as well as frequency distributions of pore channel lengths, widths, and flow path tortuosities. We observed differences in storage and transport relevant pore‐space morphological features between the two aggregates. Nodal pore volumes and throat surface areas were significantly smaller for the conventionally tilled (Conv.T.) aggregate (mode ≈ 7.9 × 10−7 mm3/≈ 63 μm2) than for the grassland aggregate (mode ≈ 5.0 × 10−6 mm3/≈ 400 μm2), respectively. Path lengths were shorter for the Conv.T. aggregate (maximum lengths < 200 μm) compared with the grassland aggregate (maximum lengths > 600 μm). In summary, the soil aggregate from the Conv.T site showed more gas and water transport limiting micromorphological features compared with the aggregate from the grassland management system.

The histidine protein kinase DcuS of Escherichia coli senses C 4 -dicarboxylates and citrate by a periplasmic domain. The closely related sensor kinase CitA binds citrate, but no C 4 -dicarboxylates, by a homologous periplasmic domain. CitA is known to bind the three carboxylate and the hydroxyl groups of citrate by sites C1, C2, C3, and H. DcuS requires the same sites for C 4 -dicarboxylate sensing, but only C2 and C3 are highly conserved. It is shown here that sensing of citrate by DcuS required the same sites. Binding of citrate to DcuS, therefore, was similar to binding of C 4 -dicarboxylates but different from that of citrate binding in CitA. DcuS could be converted to a C 4 -dicarboxylate-specific sensor (DcuS DC ) by mutating residues of sites C1 and C3 or of some DcuS-subtype specific residues. Mutations around site C1 aimed at increasing the size and accessibility of the site converted DcuS to a citrate-specific sensor (DcuS Cit ). DcuS DC and DcuS Cit had complementary effector specificities and responded either to C 4 -dicarboxylates or to citrate and mesaconate. The results imply that DcuS binds citrate (similar to the C 4 -dicarboxylates) via the C 4 -dicarboxylate part of the molecule. Sites C2 and C3 are essential for binding of two carboxylic groups of citrate or of C 4 -dicarboxylates; sites C1 and H are required for other essential purposes.Escherichia coli is able to use C 4 -dicarboxylates as substrates for anaerobic growth by fumarate respiration, which requires the synthesis of fumarate reductase (frdABCD genes) and the fumarate/succinate antiporter DcuB (dcuB gene) (for reviews, see references 6, 15, and 28). Expression of the frdABCD and dcuB genes is stimulated by the DcuSR two-component system (12,14,15,29). DcuS responds to C 4 -dicarboxylates and related compounds through a periplasmic sensing domain (19). The two carboxylic groups of the C 4 -dicarboxylates are crucial for stimulus perception, whereas other parts of the C 4 -dicarboxylates such as ligands at position C2 or C3 are of minor significance. The apparent K D values of C 4 -dicarboxylates for stimulating the expression of DcuS-regulated genes are in the range of 0.45 to 3 mM.DcuS is a member of the CitA/DcuS family of sensory histidine kinases and shares significant sequence similarities with CitA (4,5,15,17,18). CitA is the highly specific and highaffinity citrate sensor kinase of the CitAB two-component system that controls expression of the citrate fermentation genes in Klebsiella pneumoniae and E. coli. The CitA and DcuS sensors have similar membrane topologies, with a periplasmic sensory domain and a cytoplasmic kinase domain (15,18,29). CitA and DcuS are typical members of the periplasmic sensing histidine kinases (20). The structure of the periplasmic domain of DcuS has been solved by nuclear magnetic resonance (NMR) spectroscopy, and that of CitA from K. pneumoniae has been solved by crystallography and X-ray analysis (23, 25).The overall structures for the two domains are similar and resemble the PAS (Per-Arnt-Sim)...

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SummaryKallikrein-related peptidases (KLKs) constitute a family of 15 highly conserved serine proteases, which show a tissue-specific expression profile. This made them valuable tumour expression markers. It became evident that KLKs are involved in many physiological processes like semen liquefaction and skin desquamation. More recently, we have learnt that they are involved in many pathophysiological conditions and diseases making them promising target of therapeutic intervention. Therefore, regulation of KLKs raised the interest of numerous reports. Herein, we summarise the current knowledge on KLKs regulation with an emphasis on skin-relevant KLKs regulation processes.Regulation of KLKs takes place on the level of transcription, on protease activation and on protease inactivation. A variety of protease inhibitors has been described to interact with KLKs including the irreversible serine protease inhibitors (SERPINs) and the reversible serine protease inhibitors of Kazal-type (SPINKs). In an attempt to integrate current knowledge, we propose that KLK regulation has credentials as targets for therapeutic intervention.

Kallikrein-related peptidases (KLKs) play a central role in skin desquamation. They are tightly controlled by specific inhibitors, including the lymphoepithelial Kazal-type inhibitor (LEKTI) encoded by SPINK5 and LEKTI-2 encoded by SPINK9. Herein, we identify SPINK6 as a selective inhibitor of KLKs in the skin. Unlike LEKTI but similar to LEKTI-2, SPINK6 possesses only one typical Kazal domain. Its mRNA was detected to be expressed at low levels in several tissues and was induced during keratinocyte differentiation. Natural SPINK6 was purified from human plantar stratum corneum extracts. Immunohistochemical analyses revealed SPINK6 expression in the stratum granulosum of human skin at various anatomical localizations and in the skin appendages, including sebaceous glands and sweat glands. SPINK6 expression was decreased in lesions of atopic dermatitis. Using KLK5, KLK7, KLK8, KLK14, thrombin, trypsin, plasmin, matriptase, prostasin, mast cell chymase, cathepsin G, neutrophil elastase, and chymotrypsin, inhibition with recombinant SPINK6 was detected only for KLK5, KLK7, and KLK14, with apparent K i values of 1.33, 1070, and 0.5 nM, respectively. SPINK6 inhibited desquamation of human plantar callus in an ex vivo model. Our findings suggest that SPINK6 plays a role in modulating the activity of KLKs in human skin. A selective inhibition of KLKs by SPINK6 might have therapeutic potential when KLK activity is elevated.The skin protects us from water loss and mechanical damage. The surface-exposed epidermis, a self-renewing stratified squamous epithelium composed of several layers of keratinocytes, is most important for the barrier defense against these challenges. Recent discoveries have highlighted the balance of proteases and protease inhibitors as key players in both desquamation processes and epidermal barrier functions (1).Human tissue kallikreins, or kallikrein-related peptidases (KLKs), 3 are the largest family of trypsin-or chymotrypsin-like secreted serine proteases, which are encoded by 15 genes on chromosome region 19q13.4 (2). At least eight KLKs are expressed in normal skin, among which KLK5, KLK7, KLK8, and KLK14 have been reported to be most important (3-6). KLKs are capable of cleaving corneodesmosomes (7-10) and are thought to be key regulators of the desquamation process. The activity of KLKs is regulated by pH and specific protease inhibitors. The importance of epithelial protease inhibitors has been revealed impressively in Netherton syndrome (OMIM 256500), an autosomal recessive disorder caused by mutations in the gene SPINK5 (serine protease inhibitor Kazal-type 5) (11). Netherton syndrome presents as an ichthyosiform dermatosis with variable erythroderma, hair shaft defects (bamboo hair), atopic features, and growth retardation (12). Lymphoepithelial Kazal-type inhibitor (LEKTI) (13), the product of SPINK5, includes in its primary structure 15 different serine protease inhibitory domains (13). Domains 15 and 2 each comprise a typical Kazal-type structure, whereas the other domains lack a disu...