1H, 15N, and 13C backbone resonance assignments of the C4b-binding region from the S. aureus extracellular adherence protein.

The Extracellular Adherence Protein (Eap) from Staphylococcus aureus is a potent inhibitor of the classical and lectin pathways of the complement system. Previous studies have shown that Eap binds with nanomolar affinity to complement component C4b and prevents C4b binding the pro-protease, C2, thereby inhibiting formation of the pro-C3 convertase shared by the classical and lectin pathways (Woehl et al. in J Immunol 193:6161-6171, 2014). The C4b-binding and complement-inhibitory properties of Eap from S. aureus strain Mu50 lie within the two C terminal-most Eap domains (i.e. Eap34) (Woehl et al. J Immunol 193:6161-6171, 2014). Interestingly, Eap34 binds C4b with an apparent KD that is nearly 100-fold tighter than that of either Eap3 or Eap4 alone (Woehl et al. in Protein Sci 26:1595-1608, 2017). This suggests that linking these two domains into a single molecule is a significant determinant of Eap function. To better understand this property at the structural level, we undertook a solution NMR study of the ~ 23 kDa Eap34 protein. In this communication, we report that greater than 98% of the total non-proline backbone residues have been assigned. These data have been deposited in the BMRB database under the accession number 50210.