Structure and plasticity of the peptidyl-prolyl isomerase Par27 of Bordetella pertussis revealed by X-ray diffraction and small-angle X-ray scattering.

Par27 from Bordetella pertussis belongs to a newly discovered class of dimeric peptidyl-prolyl isomerase (PPIase)/chaperones from the parvulin family. It is a tripartite protein with a central PPIase domain surrounded by N- and C-terminal sub-domains (NTD and CTD). Here, the Par27 structure was characterized by X-ray crystallography, small-angle X-ray scattering and template-based modeling.

Crystallization and preliminary X-ray diffraction analysis of the peptidylprolyl isomerase Par27 of Bordetella pertussis.

Proteins with both peptidylprolyl isomerase (PPIase) and chaperone activities play a crucial role in protein folding in the periplasm of Gram-negative bacteria. Few such proteins have been structurally characterized and to date only the crystal structure of SurA from Escherichia coli has been reported. Par27, the prototype of a new group of parvulins, has recently been identified.

The peptidyl-prolyl isomerase and chaperone Par27 of Bordetella pertussis as the prototype for a new group of parvulins.

Proteins that pass through the periplasm in an unfolded state are highly sensitive to proteolysis and aggregation and, therefore, often require protection by chaperone-like proteins. The periplasm of Gram-negative bacteria is well equipped with ATP-independent chaperones and folding catalysts, including peptidyl-prolyl isomerases (PPIases). The filamentous hemagglutinin of Bordetella pertussis, which is secreted by the two-partner secretion pathway, crosses the periplasm in an unfolded conformation.

Current challenges in autotransport and two-partner protein secretion pathways.

The two-partner and autotransport pathways are widely represented in Gram-negative bacteria, essentially among pathogens. Both mediate the translocation of large proteins across the outer membrane. Deciphering the molecular mechanisms of secretion machineries as well as folding of exoproteins in the course of translocation represents a current challenge.

Secretion signal of the filamentous haemagglutinin, a model two-partner secretion substrate.

The sorting of proteins to their proper subcellular compartment requires specific addressing signals that mediate interactions with ad hoc transport machineries. In Gram-negative bacteria, the widespread two-partner secretion (TPS) pathway is dedicated to the secretion of large, mostly virulence-related proteins. The secreted TpsA proteins carry a characteristic 250-residue-long N-terminal 'TPS domain' essential for secretion, while their TpsB transporters are pore-forming proteins that specifically recognize their respective TpsA partners and mediate their translocation across the outer membrane.

Channel properties of TpsB transporter FhaC point to two functional domains with a C-terminal protein-conducting pore.

Integral outer membrane transporters of the Omp85/TpsB superfamily mediate the translocation of proteins across, or their integration into, the outer membranes of Gram-negative bacteria, chloroplasts, and mitochondria. The Bordetella pertussis FhaC/FHA couple serves as a model for the two-partner secretion pathway in Gram-negative bacteria, with the TpsB protein, FhaC, being the specific transporter of its TpsA partner, FHA, across the outer membrane. In this work, we have investigated the structure/function relationship of FhaC by analyzing the ion channel properties of the wild type protein and a collection of mutants with varied FHA secretion activities.

The crystal structure of filamentous hemagglutinin secretion domain and its implications for the two-partner secretion pathway.

Filamentous hemagglutinin (FHA), the major 230-kDa adhesin of the whooping cough agent Bordetella pertussis, is one of the most efficiently secreted proteins in Gram-negative bacteria. FHA is secreted by means of the two-partner secretion (TPS) pathway. Several important human, animal, and plant pathogens also secrete adhesins and other virulence factors by using this mode of secretion.