A “dock, lock, and latch” Structural Model for a Staphylococcal Adhesin Binding to Fibrinogen

Abstract

Gram-positive pathogens such as staphylococci contain multiple cell wall-anchored proteins that serve as an interface between the microbe and its environment. Some of these proteins act as adhesins and mediate bacterial attachment to host tissues. SdrG is a cell wall-anchored adhesin from Staphylococcus epidermidis that binds to the Bbeta chain of human fibrinogen (Fg) and is necessary and sufficient for bacterial attachment to Fg-coated biomaterials. Here, we present the crystal structures of the ligand binding region of SdrG as an apoprotein and in complex with a synthetic peptide analogous to its binding site in Fg. Analysis of the crystal structures, along with mutational studies of both the protein and of the peptide, reveals that SdrG binds to its ligand with a dynamic "dock, lock, and latch" mechanism. We propose that this mechanism represents a general mode of ligand binding for structurally related cell wall-anchored proteins of gram-positive bacteria.

Clumping Factor B, a Fibrinogen-binding MSCRAMM (Microbial Surface Components Recognizing Adhesive Matrix Molecules) Adhesin of Staphylococcus aureus, Also Binds to the Tail Region of Type I Cytokeratin 10

“…Using isothermal titration calorimetry and intrinsic tryptophan fluorescence, we confirmed that rClfB bound to the K10 tail region and measured the K D at 1.4 and 1.7 M, respectively. Leszczynski and Rose (27) The crystal structures of the minimal ligand-binding domains of ClfA, ClfB, and SdrG have been solved (28,29). 2 Each protein is composed of two domains N2 and N3 comprising variant Dev-IgG immunoglobulin folds.…”

“…Moreover, the wider Sdr family of surface proteins is predicted to have a similar modular design and Dev-IgG folds. The structure of the ligandbinding domain of SdrG both as an apoprotein and in complex with its peptide ligand showed that the protein has an open confirmation that allows access of the ligand to the binding cleft (29). A "dock lock and latch" hypothesis was proposed as the mechanism for ligand binding (29) 2 in which the ligand binds to the hydrophobic groove separating N2 and N3.…”

“…The structure of the ligandbinding domain of SdrG both as an apoprotein and in complex with its peptide ligand showed that the protein has an open confirmation that allows access of the ligand to the binding cleft (29). A "dock lock and latch" hypothesis was proposed as the mechanism for ligand binding (29) 2 in which the ligand binds to the hydrophobic groove separating N2 and N3. A structural rearrangement occurs at the C terminus of the protein such that access to and from the binding cleft is blocked and the "docked" peptide is "locked" in place (29).…”

“…A "dock lock and latch" hypothesis was proposed as the mechanism for ligand binding (29) 2 in which the ligand binds to the hydrophobic groove separating N2 and N3. A structural rearrangement occurs at the C terminus of the protein such that access to and from the binding cleft is blocked and the "docked" peptide is "locked" in place (29).…”

Structures of SdrD from Staphylococcus aureus reveal the molecular mechanism of how the cell surface receptors recognize their ligands

“…B domains share signifi cant sequence similarities, including a sequence corresponding to EF-hand motif with an identity of over 35%, and two conserved Ca 2+ binding sites with 32% and 20% identity, respectively (Josefsson et al, 1998). Previous studies into the crystal structures of ClfA, ClfB and SdrG have revealed the molecular mechanism underlying ligand-binding by A region in these MSCRAMMs (Ponnuraj et al, 2003;Ganesh et al, 2008). Typically, MSCRAMMs have been reported to bind to fi brinogen, fi bronectin, neurexin and IgGs (Hartford et al, 2001;Deivanayagam et al, 2002;Barbu et al, 2010;Ganesh et al, 2011).…”