A HEX-1 crystal lattice required for Woronin body function in Neurospora crassa.
The Woronin body is a dense-core vesicle specific to filamentous ascomycetes (Euascomycetes), where it functions to seal the septal pore in response to cellular damage. The HEX-1 protein self-assembles to form this solid core of the vesicle. Here, we solve the crystal structure of HEX-1 at 1.8 A, which provides the structural basis of its self-assembly. The structure reveals the existence of three intermolecular interfaces that promote the formation of a three-dimensional protein lattice. Consistent with these data, self-assembly is disrupted by mutations in intermolecular contact residues and expression of an assembly-defective HEX-1 mutant results in the production of aberrant Woronin bodies, which possess a soluble noncrystalline core. This mutant also fails to complement a hex-1 deletion in Neurospora crassa, demonstrating that the HEX-1 protein lattice is required for Woronin body function. Although both the sequence and the tertiary structure of HEX-1 are similar to those of eukaryotic initiation factor 5A (eIF-5A), the amino acids required for HEX-1 self-assembly and peroxisomal targeting are absent in eIF-5A. Thus, we propose that a new function has evolved following duplication of an ancestral eIF-5A gene and that this may define an important step in fungal evolution.
Yuan
Ping
P
Institute of Molecular and Cell Biology, 30 Medical Drive, The National University of Singapore, Singapore, 117609.
Jedd
Gregory
G
Kumaran
Desigan
D
Swaminathan
Subramanyam
S
Shio
Helen
H
Hewitt
David
D
Chua
Nam-Hai
NH
Swaminathan
Kunchithapadam
K
D000595:Amino Acid Sequence; D001483:Base Sequence; D018360:Crystallography, X-Ray; D004271:DNA, Fungal / Q000235:genetics; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002479:Inclusion Bodies / Q000737:chemistry / Q000648:ultrastructure; D008854:Microscopy, Electron; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009492:Neurospora crassa / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D010448:Peptide Initiation Factors / Q000737:chemistry / Q000235:genetics; D017433:Protein Structure, Secondary; D016601:RNA-Binding Proteins; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D000097574:Eukaryotic Translation Initiation Factor 5A
D004271:DNA, Fungal; D005656:Fungal Proteins; D010448:Peptide Initiation Factors; D016601:RNA-Binding Proteins; D000097574:Eukaryotic Translation Initiation Factor 5A; C426803:Woronin body major protein, Neurospora crassa