Related Experiment Videos
A mitochondrial porin cDNA predicts the existence of multiple human porins
1Department of Microbiology, University of Alabama, Birmingham 35294.
Abstract:
Pores formed in the outer membrane of mitochondria by mitochondrial porin make it permeable to water-soluble metabolites smaller than approximately 5 kDa. We have isolated a full-length cDNA encoding a human porin. This probe detects a single approximately 1.5-kilobase mRNA species on Northern blots, but multiple hybridizing bands on genomic Southern blots. The open reading frame predicts a 38.1-kDa protein with a pI of 6.59 that is homologous but not identical to a previously reported protein sequence of a 31-kDa porin isolated from human lymphocytes (porin 31HL). The most striking difference between the two porins is that the sequence predicted by the cDNA is longer than the 31HL porin by 27 amino acids at the amino terminus and 38 amino acids at the carboxyl terminus. The porin cDNA directs the in vitro translation of two protein species of approximately 32 and approximately 36 kDa, which appear to result from alternate usage of AUG initiation codons. The 32-kDa protein is the predominant species imported into both rat and yeast mitochondria in vitro. Taken together, these results suggest that multiple porin proteins can be expressed in humans. Additionally, a porin consensus protein sequence has been identified that is conserved in eukaryotic organisms as diverse as yeast and man.
Insights
Researchers identified a human porin gene, revealing it can produce multiple porin proteins. This suggests diverse mitochondrial porin expression in humans, conserved across eukaryotes.
Area of Science:
- Mitochondrial biology
- Molecular genetics
Background:
- Mitochondrial outer membrane porins regulate metabolite transport.
- Understanding human porin diversity is crucial for mitochondrial function.
Purpose of the Study:
- To isolate and characterize a full-length cDNA encoding a human porin.
- To investigate the expression and potential diversity of human porins.
Main Methods:
- Isolation of full-length human porin cDNA.
- Northern and Southern blot analyses.
- In vitro translation and mitochondrial import assays.
Main Results:
- A human porin cDNA was isolated, predicting a 38.1-kDa protein homologous to known porins.
- Northern blots showed a single mRNA species, while Southern blots indicated multiple gene loci.
- In vitro translation produced 32-kDa and 36-kDa proteins, with the 32-kDa form preferentially imported into mitochondria.
- Sequence analysis revealed significant differences compared to a previously identified human lymphocyte porin (porin 31HL).
Conclusions:
- Human porins exhibit sequence diversity and can be expressed as multiple protein isoforms.
- Alternative initiation codon usage contributes to porin heterogeneity.
- A conserved porin consensus sequence exists across diverse eukaryotic organisms.