Deconstructing woronin body formation

Abstract

The Woronin body is a peroxisomally derived organelle unique to Euascomycetes. These are colonial coenocytes, with multinuclear septate tubular hyphae with central pores permitting unrestricted movement of cellular organelles. Following hyphal damage, cytoplasmic pressure distorts cellular components out of hyphae. The Woronin body with its dense central core of HEX-1, functions by occluding septal pores of injured hyphae and preventing loss of cellular components. The assembly of HEX-1 is mediated by the intermolecular interfaces between three distinct groups comprising its crystal lattice. The significance of these residues was highlighted by previous research on the H39G mutant, which displays a complete failure of HEX-1 self-assembly and function and loss of the characteristic peroxisomal dimorphism observed in the wild type. Based on the hypothesis that feedback involving a structural component of the HEX-1 matrix proteins controls peroxisomal size and Woronin body function, mutations disrupting group interfaces were introduced into HEX-1. Group I and II mutants displayed minor effects on self-assembly while continuing to generate larger peroxisomes. In contrast a Group III mutant possessed neither larger peroxisomes nor visible Woronin bodies and displayed kinetic defects in the import of a peroxisomally tagged GFP. These results are consistent with the Group III interface playing a key role in mediating Woronin body assembly.