: During the past funding period, we have solved the structures of the ligand binding domains of several MSCRAMMs both as apo-proteins and in complex with synthetic peptides mimicking their ligands. These studies have revealed that staphylococcal MSCRAMMs have very similar structures where the ligand binding A domains are composed of three subdomains each adopting an IgG-like fold. By examining different genomic databases, we have come to realize that up to 50% of the Cell Wall Anchored proteins of different Gram-positive pathogens can be identified as orphan MSCRAMMs. Analyses of MSCRAMM crystal structures also allowed us to postulate a unique ligand binding mechanism for the interaction of SdrG with fibrinogen that we called """"""""Dock, Lock and Latch"""""""" (D, L & L). The now proposed study is focused around the """"""""D, L, & L model of ligand binding and in specific aim 1) we will analyse this binding model in detail. Preliminary data indicate that other staphylococcal fibrinogen binding MSCRAMMs may use distinct variants of the D, L & L mechanism for ligand binding and in specific aim 2) we will explore these ideas. A different but related ligand binding mechanism (Wrap and Latch) is proposed for the collagen binding MSCRAMMs CNA and ACE and is based on prelimarily analyses of a crystal structure of CNA in complex with a synthetic collagen-like triple helix peptide (specific aim 3). We will use very similar biochemical techniques in the analyses of the different ligand binding models which will allow us the best base for comparisons. Finally in specific aim 4 we will use the data generated in the previous aims to develop a molecular modeling strategy to identify new ligands for orphan MSCRAMMs.
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