Discovery of antivirulence agents against methicillin-resistant Staphylococcus aureus.

Antivirulence agents inhibit the production of disease-causing virulence factors but are neither bacteriostatic nor bactericidal. Antivirulence agents against methicillin-resistant Staphylococcus aureus (MRSA) strain USA300, the most widespread community-associated MRSA strain in the United States, were discovered by virtual screening against the response regulator AgrA, which acts as a transcription factor for the expression of several of the most prominent S. aureus toxins and virulence factors involved in pathogenesis.

The specificity and function of the metal-binding sites in the integrin beta3 A-domain.

The A-domains within integrin beta subunits contain three metal sites termed the metal ion-dependent adhesion site (MIDAS), site adjacent to the metal ion-dependent adhesion site (ADMIDAS), and ligand-induced metal-binding site (LIMBS), and these sites are involved in ligand engagement. The selectivity of these metal sites and their role in ligand binding have been investigated by expressing a fragment corresponding to the beta3 A-domain, beta3-(109-352), and single point mutants in which each of the cation-binding sites has been disabled. Equilibrium dialysis experiments identified three Mn2+- and two Ca2+-binding sites with the LIMBS being the site that did not bind Ca2+.

Regulation of integrin alphaIIbbeta3 activation by distinct regions of its cytoplasmic tails.

The short cytoplasmic tails regulate activation of integrin adhesion receptors via clasping/unclasping of their membrane-proximal helices. Using integrin alpha(IIb)beta(3) as a model, we show that a previously reported activating mutation alpha(IIb)(R(995)D) that perturbs the electrostatic interface in the clasp only partially activates alpha(IIb)beta(3) and that extensive activation of the receptor is achieved by complete deletion of alpha(IIb) CT or triple mutations in alpha(IIb)(V(990)A/F(992)A/R(995)D) that disrupt both electrostatic and hydrophobic interfaces in the clasp. The results provide quantitative evidence for an equilibrium-based integrin activation process where shifting the equilibrium to the fully activated state requires total unclasping of the cytoplasmic tails.