Cholesterol Dependent Cytolysins (CDCs) are a family of pore forming toxins produced by a broad range of bacteria.  These toxins are secreted as soluble monomers, which bind to target membranes, oligermerize, and undergo a large conformational change, partially inserting into the host membranes to form a large transmembrane pores.

For membrane binding CDCs have a strict requirement and specifically interact with cholesterol, although the structural requirements of the CDC-Cholesterol interaction are unknown. We are investigating interactions between the CDC monomers and host membrane lipids, specifically cholesterol.  Difficulties studying this interaction arise due to the conformational change that occurs upon membrane binding.  Bioinformatic analyses have identified a protein, Alr1329, produced by the cyanobacteria Nostocaceae with partial homology to the CDC family.  Alr1329 appears to contain a CDC-like membrane binding domain, but has a metallophosphatase domain in place of the membrane inserting domain.  It is anticipated that without the insertion domain, this protein will be more amenable to characterization of membrane interaction. We have performed preliminary characterization including membrane binding assays, phosphatase activity assays and crystallography studies; results from these will be presented. Analysis of Alr1329 will shed light on how CDCs interact with host membranes.