Neisserial Opa Protein Loop Dynamics and Mechanism of Interaction with Host CEACAM Receptors

Abstract

Neisseria gonorrhoeae and N. meningitides are human pathogens which infect millions each year and are becoming increasingly antibiotic resistant. These bacteria utilize opacity-associated (Opa) proteins to mediate bacterial uptake into non-phagocytic and phagocytic cells as a means of infection. Opa proteins primarily engage carcinoembryonic antigen-related cellular adhesion molecules (CEACAMs), hijacking host cellular mechanisms to induce bacterial engulfment. The Opa family of proteins are outer membrane β-barrels with eight transmembrane strands and four extracellular loops. Opa proteins bind CEACAMs with high affinity and specificity, yet the loops important to receptor engagement are highly diverse in sequence among Opa variants. We aim to determine how sequence diversity in the receptor-interacting domains of Opa loops facilitates engagement of CEACAM receptors. Results from CW-EPR and NMR relaxation experiments indicate the Opa loops are dynamic on the nanosecond timescale in lipid and detergent environments. Such flexibility may enable sampling of transient structures and interactions that promote receptor engagement. To determine if the conformation of the bound loops is sampled, the structure of the Opa-CEACAM complex is needed. Towards this end, a model of the Opa60-CEACAM1 binding complex will be determined using a hybrid Double Electron Electron Resonance (DEER) and molecular dynamics (MD) approach. DEER distances between Opa60 and CEACAM1 provide spatial restraints for MD simulations of the complex, and preliminary models will be presented. Elucidating the mechanism of Opa-receptor interactions will augment our understanding of the determinants promoting the entry of a foreign body into non-phagocytic cells.