N,N'-dicyclohexylcarbodiimide cross-linking suggests a central core of helices II in oligomers of URF13, the pore-forming T-toxin receptor of cms-T maize mitochondria.
Published
Journal Article
URF13 is a mitochondrially encoded, integral membrane protein found only in maize carrying the cms-T cytoplasm. URF13 is associated with cytoplasmic male sterility, Texas type, and causes susceptibility to the fungal pathogens Bipolaris maydis race T and Phyllosticta maydis. URF13 is predicted to contain three transmembrane alpha-helices and is a receptor for the pathotoxins (T-toxins) produced by B. maydis race T and P. maydis. Binding of T-toxin to URF13 leads to membrane permeability. Cross-linking of URF13 oligomers with N,N'-dicyclohexylcarbodiimide (DCCD) protects Escherichia coli cells expressing URF13 and cms-T mitochondria from the permeability caused by T-toxin or methomyl. Using mutated forms of URF13 expressed in E. coli cells, we determined the molecular mechanism of DCCD protection. We separately changed Lys-37 in helix II to isoleucine (K37I-URF13) and Lys-32 in the helix I/helix II loop region to alanine (K32A-URF13). DCCD treatment of K37I-URF13-expressing cells did not protect the cells from permeability caused by T-toxin or methomyl. DCCD cross-linking was greatly reduced in K37I-URF13 and in D39V-URF13-expressing cells, but it was unaffected in K32A-URF13-expressing cells. Binding of methomyl or T-toxin decreases DCCD cross-linking of URF13 oligomers expressed in either E. coli or cms-T mitochondria. We conclude that Asp-39 in helix II is cross-linked by DCCD to Lys-37 in helix II of an adjacent URF13 molecule and that this cross-linking protects against toxin-mediated permeabilization. Our results also indicate that helices II form a central core in URF13 oligomers.
Full Text
Duke Authors
Cited Authors
- Rhoads, DM; Kaspi, CI; Levings, CS; Siedow, JN
Published Date
- August 1994
Published In
Volume / Issue
- 91 / 17
Start / End Page
- 8253 - 8257
PubMed ID
- 8058790
Pubmed Central ID
- 8058790
Electronic International Standard Serial Number (EISSN)
- 1091-6490
International Standard Serial Number (ISSN)
- 0027-8424
Digital Object Identifier (DOI)
- 10.1073/pnas.91.17.8253
Language
- eng