Energetic communication between functional sites of the gene-3-protein during infection by phage fd.

To initiate infection of Escherichia coli, phage fd uses its gene-3-protein (G3P) to bind first to an F pilus and then to the TolA protein at the cell surface. G3P is normally auto-inhibited because a tight interaction between the two N-terminal domains N1 and N2 buries the TolA binding site. Binding of N2 to the pilus activates G3P by initiating long-range conformational changes that are relayed to the domain interface and to a proline timer.

Initiation of phage infection by partial unfolding and prolyl isomerization.

Infection of Escherichia coli by the filamentous phage fd starts with the binding of the N2 domain of the phage gene-3-protein to an F pilus. This interaction triggers partial unfolding of the gene-3-protein, cis → trans isomerization at Pro-213, and domain disassembly, thereby exposing its binding site for the ultimate receptor TolA. The trans-proline sets a molecular timer to maintain the binding-active state long enough for the phage to interact with TolA.

Yersinia enterocolitica and Photorhabdus asymbiotica β-lactamases BlaA are exported by the twin-arginine translocation pathway.

In general, β-lactamases of medically important Gram-negative bacteria are Sec-dependently translocated into the periplasm. In contrast, β-lactamases of Mycobacteria spp. (BlaC, BlaS) and the Gram-negative environmental bacteria Stenotrophomonas maltophilia (L2) and Xanthomonas campestris (Bla(XCC-1)) have been reported to be secreted by the twin-arginine translocation (Tat) system.

A kinetic approach to determining the conformational stability of a protein that dimerizes after folding.

A strongly stabilized form of the β1 domain of the streptococcal protein G, termed Gβ1-M2, was previously obtained by an in vitro selection method for stabilized protein variants. It contains four substitutions, but how they contribute to the Gibbs free energy of denaturation (ΔG(D)) could not be determined, because, unlike the wild-type protein, Gβ1-M2 dimerizes in a spectroscopically silent reaction. Here we determined the ΔG(D) of the folded Gβ1-M2 monomer by using a kinetic approach that uncouples the folding of the monomer from dimerization.