PapD chaperone

Fig. 2. Ribbon model of the three-dimensional structure of the PapD chaperone. The consensus sequence for twelve members of the family was superimposed on the tertiary structure of PapD. The position of the invariant amino acid residues is shown in black, and that of the residues conserved in at least eight of the sequences, in gray.

Fig. 3. Periplasmic pilus chaperone consensus sequence. Amino acid sequence of the PapD chaperone (top line) and consensus sequence derived from the comparison of twelve chaperones (second line). Amino acids are indicated using the one-letter code. In the consensus sequence, a letter shows a residue that is present in at least eight out of twelve sequences, an asterisk designates an invariant residue, and a box shows a position with a hydrophobic residue in all twelve periplasmic chaperones. The arrows underneath the sequence represent the /3 strands found in the PapD structure.

Fig. 4. (A) Space-filling model of the PapD chaperone. The solvent-exposed conserved...

Fig. 7. Three different binding sites used by the immunoglobulin-like proteins tbe PapD chaperone, the antigen-binding fragment of an immunoglobulin (Fab ), and the human growth hormone-binding protein (hCHbp). Each immunoglobulin-like domain is...

The ability of the PapD chaperone to bind transiently to pilus subunits and cap interactive surfaces allows the subunits to pass through the periplasm without aggregation. The uncapping of PapD at the outer membrane seems to expose polymerization sites and drive assembly. The mechanism of chaperone uncapping is unknown but is seemingly ATP independent and may involve PapC. 

The three-dimensional structure of the PapD periplasmic chaperone that forms transient complexes with pilus subunit proteins has been solved by Holmgren and Branden (1989). PapD consists of two globular domains oriented in the shape of a boomerang (Fig. 2). Each domain is a /3-barrel structure formed by two antiparallel /8-pleated sheets that have a topology similar to an immunoglobulin fold. The relationship between PapD and other immunoglobulin-like proteins is discussed in Section IV,C. 

Recent studies have shown that the recognition of pilus subunit proteins by PapD involves the conserved cleft of the chaperone (Slonim et... 

PapD and PapC appear to act as molecular escorts, regulating the interactions of each pilus protein. As a molecular chaperone, PapD prevents nonproductive interactions of the subunits and allows the subunits to fold properly. We propose that PapC is a member of a new class of proteins that we have named molecular ushers. The PapC usher acts as... 

PapD and Superfamily of Periplasmic Immunoglobulin-like Pilus Chaperones... 

PapD Membrane chaperones Absent from Eukarya Shr3p Gsf2p Pho68p Chs7p Present in some Prevention of aggregation of subunits of pUi Prevent aggregation of some integral polytopic membrane proteins... 

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