Atomic force microscopy images suggest aggregation mechanism in cerato-platanin

Abstract Cerato-platanin (CP), the first member of the''cerato-platanin family'', is a moderately hydrophobicprotein produced by Ceratocystis fimbriata, the causalagent of a severe plant disease called ''canker stain''.The protein is localized in the cell wall of the fungusand it seems to be involved in the host-plane interactionand induces both cell necrosis and phytoalexin synthesis(one of the first plant defence-related events). Recently, ithas been determined that CP, like other fungal surfaceprotein, is able to self assemble in vitro. In this paper wecharacterize the aggregates of CP by Atomic ForceMicroscopy (AFM) images. We observe that CP tendsto form early annular-shaped oligomers that seem toconstitute the fundamental bricks of a hierarchicalaggregation process, eventually resulting in large macrofibrillarassemblies. A simple model, based on thehypothesis that the aggregation is energetically favourablewhen the exposed surface is reduced, is compatiblewith the measured aggregates' shape and size. The proposedmodel can help to understand the mechanism bywhich CP and many other fungal surface proteins exerttheir effects.