Members of this family of plant pathogenic proteins adopt an elongated structure somewhat reminiscent of a mushroom that can be divided into 'stalk' and 'head' subdomains. The stalk subdomain is composed of the N-terminal helix (alpha1) and beta strands beta3-beta4. An antiparallel beta sheet (beta5, beta7-beta8) forms the base of the head subdomain that interacts with the stalk. A pair of twisted antiparallel beta sheets (beta1 and beta6; beta2 and beta9/9') supported by alpha2 form the dome of the head. The head subdomain possesses weak structural similarity with the catalytic portion of a number of ADP-ribosyltransferase toxins [1].

1: Crystal structures of the type III effector protein AvrPphF and its chaperone reveal residues required for plant pathogenesis. Singer AU, Desveaux D, Betts L, Chang JH, Nimchuk Z, Grant SR, Dangl JL, Sondek J; Structure. 2004;12:1669-1681. PMID:15341731