Structural basis for vinculin activation at sites of cell adhesion

Vinculin is a highly conserved intracellular protein with a crucial role in the maintenance and regulation of cell adhesion and migration. In the cytosol, vinculin adopts a default autoinhibited conformation. On recruitment to cell-cell and cell-matrix adherens-type junctions, vinculin becomes activated and mediates various protein-protein interactions that regulate the links between F-actin and the cadherin and integrin families of cell-adhesion molecules. Here we describe the crystal structure of the full-length vinculin molecule (1,066 amino acids), which shows a five-domain autoinhibited conformation in which the carboxy-terminal tail domain is held pincer-like by the vinculin head, and ligand binding is regulated both sterically and allosterically. We show that conformational changes in the head, tail and proline-rich domains are linked structurally and thermodynamically, and propose a combinatorial pathway to activation that ensures that vinculin is activated only at sites of cell adhesion when two or more of its binding partners are brought into apposition.     

Pervasive alteration of tree communities in undisturbed Amazonian forests

Amazonian rainforests are some of the most species-rich tree communities on earth. Here we show that, over the past two decades, forests in a central Amazonian landscape have experienced highly nonrandom changes in dynamics and composition. Our analyses are based on a network of 18 permanent plots unaffected by any detectable disturbance. Within these plots, rates of tree mortality, recruitment and growth have increased over time. Of 115 relatively abundant tree genera, 27 changed significantly in population density or basal area--a value nearly 14 times greater than that expected by chance. An independent, eight-year study in nearby forests corroborates these shifts in composition. Contrary to recent predictions, we observed no increase in pioneer trees. However, genera of faster-growing trees, including many canopy and emergent species, are increasing in dominance or density, whereas genera of slower-growing trees, including many subcanopy species, are declining. Rising atmospheric CO2 concentrations may explain these changes, although the effects of this and other large-scale environmental alterations remain uncertain. These compositional changes could have important impacts on the carbon storage, dynamics and biota of Amazonian forests.     

Comparative analysis of the genome sequences of Bordetella pertussis,Bordetella parapertussis and Bordetella bronchiseptica

Bordetella pertussis, Bordetella parapertussis and Bordetella bronchiseptica are closely related Gram-negative beta-proteobacteria that colonize the respiratory tracts of mammals. B. pertussis is a strict human pathogen of recent evolutionary origin and is the primary etiologic agent of whooping cough. B. parapertussis can also cause whooping cough, and B. bronchiseptica causes chronic respiratory infections in a wide range of animals. We sequenced the genomes of B. bronchiseptica RB50 (5,338,400 bp; 5,007 predicted genes), B. parapertussis 12822 (4,773,551 bp; 4,404 genes) and B. pertussis Tohama I (4,086,186 bp; 3,816 genes). Our analysis indicates that B. parapertussis and B. pertussis are independent derivatives of B. bronchiseptica-like ancestors. During the evolution of these two host-restricted species there was large-scale gene loss and inactivation; host adaptation seems to be a consequence of loss, not gain, of function, and differences in virulence may be related to loss of regulatory or control functions.     

Hidden complexity in the mechanical properties of titin

Individual molecules of the giant protein titin span the A-bands and I-bands that make up striated muscle. The I-band region of titin is responsible for passive elasticity in such muscle, and contains tandem arrays of immunoglobulin domains. One such domain (I27) has been investigated extensively, using dynamic force spectroscopy and simulation. However, the relevance of these studies to the behaviour of the protein under physiological conditions was not established. Force studies reveal a lengthening of I27 without complete unfolding, forming a stable intermediate that has been suggested to be an important component of titin elasticity. To develop a more complete picture of the forced unfolding pathway, we use mutant titins--certain mutations allow the role of the partly unfolded intermediate to be investigated in more depth. Here we show that, under physiological forces, the partly unfolded intermediate does not contribute to mechanical strength. We also propose a unified forced unfolding model of all I27 analogues studied, and conclude that I27 can withstand higher forces in muscle than was predicted previously.