Abstract/Summary

Chlamydiapneumoniaeis a Gram-negative bacterium responsible for a number of humanrespiratory diseases and linked to some chronic inflammatory diseases. The major outer membraneprotein (MOMP) ofChlamydiais a conserved immunologically dominant protein located in the outermembrane, which, together with its surface exposure and abundance, has led to MOMP being themain focus for vaccine and antimicrobial studies in recent decades. MOMP has a major role in thechlamydial outer membrane complex through the formation of intermolecular disulphide bonds,although the exact interactions formed are currently unknown. Here, it is proposed that due to thelarge number of cysteines available for disulphide bonding, interactions occur between cysteine-richpockets as opposed to individual residues. Such pockets were identified using a MOMP homologymodel with a supporting low-resolution (~4 Å) crystal structure. The localisation of MOMP in theE. colimembrane was assessed using direct stochastic optical reconstruction microscopy (dSTORM),which showed a decrease in membrane clustering with cysteine-rich regions containing two mutations.These results indicate that disulphide bond formation was not disrupted by single mutants locatedin the cysteine-dense regions and was instead compensated by neighbouring cysteines within thepocket in support of this cysteine-rich pocket hypothesis.