title: Deletion variants of Neurospora mitochondrial porin: electrophysiological and spectroscopic analysis.
abstract: Mitochondrial porins are predicted to traverse the outer membrane as a series of beta-strands, but the precise structure of the resulting beta-barrel has remained elusive. Toward determining the positions of the membrane-spanning segments, a series of small deletions was introduced into several of the predicted beta-strands of the Neurospora crassa porin. Overall, three classes of porin variants were identified: i), those producing large, stable pores, indicating deletions likely outside of beta-strands; ii), those with minimal pore-forming ability, indicating disruptions in key beta-strands or beta-turns; and iii), those that formed small unstable pores with a variety of gating and ion-selectivity properties. The latter class presumably results from a subset of proteins that adopt an alternative barrel structure upon the loss of stabilizing residues. Some variants were not sufficiently stable in detergent for structural analysis; circular dichroism spectropolarimetry of those that were did not reveal significant differences in the overall structural composition among the detergent-solubilized porin variants and the wild-type protein. Several of the variants displayed altered tryptophan fluorescence profiles, indicative of differing microenvironments surrounding these residues. Based on these results, modifications to the existing models for porin structure are proposed.
authors.affiliation: Department of Microbiology, University of Manitoba, Winnipeg, Manitoba, R3T 2N2 Canada.
authors.forename: Greg
authors.initials: G
authors.lastname: Runke
authors.forename: Elke
authors.initials: E
authors.lastname: Maier
authors.forename: William A T
authors.initials: WA
authors.lastname: Summers
authors.forename: Denice C
authors.initials: DC
authors.lastname: Bay
authors.forename: Roland
authors.initials: R
authors.lastname: Benz
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Court
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D003902:Detergents / Q000494:pharmacology; D004594:Electrophysiology; D014644:Genetic Variation; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D008958:Models, Molecular; D009492:Neurospora crassa / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D011487:Protein Conformation / Q000187:drug effects; D017510:Protein Folding; D017384:Sequence Deletion; D013050:Spectrometry, Fluorescence; D050994:Voltage-Dependent Anion Channels / Q000737:chemistry / Q000235:genetics* / Q000502:physiology
chemical_list: D003902:Detergents; D024101:Mitochondrial Proteins; D050994:Voltage-Dependent Anion Channels