Preface. Developmental Morphodynamics - bridging the gap between the genome and embryo physics.

We, the Guest Editors of this Special Issue of The International Journal of Developmental Biology, are two older embryologists, who are trying to bridge the current chasm between Entwicklungsmechanic, the developmental mechanics of our embryogenesis forefathers, and the modern movement of molecular developmental biology. Our rallying cry is that of Wilhelm His: "To think that heredity will build organic beings without mechanical means is a piece of unscientific mysticism" (His, 1888). Until recently, this claim appeared to us to fall on the somewhat deaf ears of molecular developmental biologists. Yet, the world is still one, and both physics and chemistry obviously have their place in embryogenesis. Indeed, at the molecular level, membrane proteins which are mechanoreceptors and motor molecules may begin to point the way. Here, we and our colleagues will make the case for a more equitable consideration of molecules and mechanics.     

Structural and dynamic characterization of a vinculin binding site in the talin rod

Talin is a key protein involved in linking integrins to the actin cytoskeleton. The long flexible talin rod domain contains a number of binding sites for vinculin, a cytoskeletal protein important in stabilizing integrin-mediated cell-matrix junctions. Here we report the solution structure of a talin rod polypeptide (residues 1843-1973) which contains a single vinculin binding site (VBS; residues 1944-1969). Like other talin rod polypeptides, it consists of a helical bundle, in this case a four-helix bundle with a right-handed topology. The residues in the VBS important for vinculin binding were identified by studying the binding of a series of VBS-related peptides to the vinculin Vd1 domain. The key binding determinants are buried in the interior of the helical bundle, suggesting that a substantial structural change in the talin polypeptide is required for vinculin binding. Direct evidence for this was obtained by NMR and EPR spectroscopy. [1H,15N]-HSQC spectra of the talin fragment indicate that vinculin binding caused approximately two-thirds of the protein to adopt a flexible random coil. For EPR spectroscopy, nitroxide spin labels were attached to the talin polypeptide via appropriately located cysteine residues. Measurements of inter-nitroxide distances in doubly spin-labeled protein showed clearly that the helical bundle is disrupted and the mobility of the helices, except for the VBS helix, is markedly increased. Binding of vinculin to talin is thus a clear example of the unusual phenomenon of protein unfolding being required for protein/protein interaction.     

Pyrrolidine-5,5-trans-lactams as novel mechanism-based inhibitors of human cytomegalovirus protease. Part 3: potency and plasma stability

Mechanism-based inhibitors of HCMV protease, which are stable to human plasma (> or = 20 h) and have single-figure potency in the microM range against HCMV protease, have been developed based on the dansylproline alpha-methyl pyrrolidine-5,5-trans-lactam nucleus.     

Protein stability: the COP9 signalosome gets in on the act

The COP9 signalosome is a multiprotein complex somewhat similar to the lid component of the 26S proteasome. Recent studies suggest that it regulates the stability of proteins by interfering with the ubiquitin-proteasome pathway via deneddylation and phosphorylation.     

The mouse: An “average” homeotherm

Mice, rats, and nearly all mammals and birds are classified as homeothermic, meaning that their core temperature is regulated at a constant level over a relatively wide range of ambient temperatures. In one sense, this homeothermic designation has been confirmed by the advent of radiotelemetry and other techniques that allow for the remote monitoring of awake, unrestrained animals in laboratory or natural settings. This technology confirmed that, when averaged over many hours, core temperature of mammals is regulated at a nearly constant level. On the other hand, telemetric sampling in relatively small mammals such as mice and rats also revealed that their core temperature often varies markedly from hour to hour. In other words, the mouse could be defined as a homeotherm only when core temperature is averaged over a relatively long period. Many researchers ascribe equal homeothermic capabilities to mice and other small rodents as they do to humans. Such an assumption could lead to errors in extrapolating physiological, pharmacological, and toxicological findings from experimental test species to humans.     

Activation of myeloid cell-specific adhesion class G protein-coupled receptor EMR2 via ligation-induced translocation and interaction of receptor subunits in lipid raft microdomains

The adhesion class G protein-coupled receptors (adhesion-GPCRs) play important roles in diverse biological processes ranging from immunoregulation to tissue polarity, angiogenesis, and brain development. These receptors are uniquely modified by self-catalytic cleavage at a highly conserved GPCR proteolysis site (GPS) dissecting the receptor into an extracellular subunit (α) and a seven-pass transmembrane subunit (β) with cellular adhesion and signaling functions, respectively. Using the myeloid cell-restricted EMR2 receptor as a paradigm, we exam the mechanistic relevance of the subunit interaction and demonstrate a critical role for GPS autoproteolysis in mediating receptor signaling and cell activation. Interestingly, two distinct receptor complexes are identified as a result of GPS proteolysis: one consisting of a noncovalent α-β heterodimer and the other comprising two completely independent receptor subunits which distribute differentially in membrane raft microdomains. Finally, we show that receptor ligation induces subunit translocation and colocalization within lipid rafts, leading to receptor signaling and inflammatory cytokine production by macrophages. Our present data resolve earlier conflicting results and provide a new mechanism of receptor signaling, as well as providing a paradigm for signal transduction within the adhesion-GPCR family.