Substrate specificity of a peptidyl-aminoacyl-l/d-isomerase from frog skin

In the skin of fire-bellied toads (Bombina species), an aminoacyl-l/d-isomerase activity is present which catalyses the post-translational isomerization of the l- to the d-form of the second residue of its substrate peptides. Previously, this new type of enzyme was studied in some detail and genes potentially coding for similar polypeptides were found to exist in several vertebrate species including man. Here, we present our studies to the substrate specificity of this isomerase using fluorescence-labeled variants of the natural substrate bombinin H with different amino acids at positions 1, 2 or 3. Surprisingly, this enzyme has a rather low selectivity for residues at position 2 where the change of chirality at the alpha-carbon takes place. In contrast, a hydrophobic amino acid at position 1 and a small one at position 3 of the substrate are essential. Interestingly, some peptides containing a Phe at position 3 also were substrates. Furthermore, we investigated the role of the amino-terminus for substrate recognition. In view of the rather broad specificity of the frog isomerase, we made a databank search for potential substrates of such an enzyme. Indeed, numerous peptides of amphibia and mammals were found which fulfill the requirements determined in this study. Expression of isomerases with similar characteristics in other species can therefore be expected to catalyze the formation of peptides containing d-amino acids

Soft tissue management: flap design, incision, tissue elevation and tissue retraction

The ultimate goal in surgical endodontics is not only the eradication of periapical pathosis but also preservation of periodontal conditions using suitable surgical techniques. Acceptable treatment outcomes are no longer possible without consideration of esthetic consequences for all involved dentoalveolar structures. During surgical endodontics the cortical bone is exposed by incising, elevating, and reflecting a full-thickness tissue flap. Certain basic principles must be considered before deciding on the type of incision and flap design. Thorough knowledge of regional anatomical structures in conjunction, as well as prevailing periodontal conditions affect and must be considered when making the proper decision on how and where to reflect the mucoperiosteal tissues. Various modes of incision can be selected, including horizontal, sulcular, submarginal, and vertical releasing incisions. The variety of flaps reflects the number of variables to be considered before choosing an appropriate flap design. While many flap designs have been suggested over the years, some have become obsolete and new techniques have emerged. It is critical that incisions and tissue elevations and reflections are performed in a way that facilitates healing by primary intention. This can be obtained by complete and sharp incision avoiding severing or traumatizing the tissues during elevation; it is equally important to prevent drying of tissue remnants on the root surface and drying of the flap during the procedure. The introduction of microsurgery to surgical endodontics attempts to minimize trauma and to enhance surgical results. Because of the combination of magnification and more delicate instruments, improved and careful tissue handling has become possible. Additional improvements in flap design and soft tissue manipulation are considered key elements in enhanced biological and esthetic outcomes of marginal soft tissues

Arabidopsis MAP kinase 4 regulates gene expression through transcription factor release in the nucleus

Plant and animal perception of microbes through pathogen surveillance proteins leads to MAP kinase signalling and the expression of defence genes. However, little is known about how plant MAP kinases regulate specific gene expression. We report that, in the absence of pathogens, Arabidopsis MAP kinase 4 (MPK4) exists in nuclear complexes with the WRKY33 transcription factor. This complex depends on the MPK4 substrate MKS1. Challenge with Pseudomonas syringae or flagellin leads to the activation of MPK4 and phosphorylation of MKS1. Subsequently, complexes with MKS1 and WRKY33 are released from MPK4, and WRKY33 targets the promoter of PHYTOALEXIN DEFICIENT3 (PAD3) encoding an enzyme required for the synthesis of antimicrobial camalexin. Hence, wrky33 mutants are impaired in the accumulation of PAD3 mRNA and camalexin production upon infection. That WRKY33 is an effector of MPK4 is further supported by the suppression of PAD3 expression in mpk4–wrky33 double mutant backgrounds. Our data establish direct links between MPK4 and innate immunity and provide an example of how a plant MAP kinase can regulate gene expression by releasing transcription factors in the nucleus upon activation