Interaction of the Curli Accessory Proteins CsgE and CsgF with the Human Islet Amyloid Polypeptide

Abstract

Gram-negative bacteria, such as E.coli and Salmonella, contain proteinaceous, hair-like, cell surface filaments known as curli. Curli serve to facilitate cell-cell interactions and are essential for host cell colonization. Curli assembly involves six proteins, CsgA, CsgB, CsgC, CsgE, CsgF, and CsgG. CsgE and CsgF are thought to act as chaperones to help prevent the premature aggregation of CsgA and/or CsgB, and to help transport these proteins, through the outer-membrane protein CsgG, to the cell surface where they assemble to form curli. We have observed that both CsgE and CsgF are able to inhibit the aggregation of CsgA, as well as human Islet Amyloid Polypeptide (hIAPP), an amyloidogenic polypeptide that is unrelated to curli. We are investigating the nature of the CsgE/CsgF interaction with hIAPP using a series of single cysteine mutants of the two proteins and fluorescence spectroscopy. Fluorescence quenching studies indicate that the C-terminal regions of CsgE/CsgF may be involved in interacting with hIAPP.