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Evolutionary specialization of the nuclear targeting apparatus
H S Malik1, T H Eickbush, D S Goldfarb
1Department of Biology, University of Rochester, Rochester, NY 14627, USA.
Summary
Alpha- and beta-karyopherins (Kaps) are crucial for nuclear transport. This study reveals structural similarities between their repeat domains, suggesting they belong to the same protein superfamily and evolved from a common ancestor.
Area of Science:
- Molecular Biology
- Evolutionary Biology
- Cell Biology
Background:
- Nuclear transport of proteins is mediated by alpha- and beta-karyopherins (Kaps), also known as importins.
- Alpha-Kaps possess a conserved domain of eight tandemly arranged armadillo-like (Arm) repeats.
- Beta-Kaps are characterized by 14-15 tandemly arranged HEAT motifs.
Purpose of the Study:
- To investigate the evolutionary relationship and structural similarities between alpha- and beta-karyopherins.
- To explore the phylogenetic distribution and potential functional divergence of Kaps across different species.
Main Methods:
- Phylogenetic analysis of alpha- and beta-karyopherin sequences.
- Comparative structural analysis of Arm repeats and HEAT motifs.
Main Results:
- The Arm repeats of alpha-Kaps and HEAT motifs of beta-Kaps exhibit significant structural similarity.
- Phylogenetic analysis reveals two main groups of alpha-Kaps (alpha1 and alpha2) and at least three groups of beta-Kaps.
- A model is proposed where alpha-independent beta-Kap progenitors evolved into alpha-dependent beta-Kaps and alpha-Kaps.
Conclusions:
- Alpha- and beta-Kaps, along with other repeat-containing proteins, likely belong to the same superfamily, indicating a shared evolutionary origin.
- The findings provide insights into the diversification of karyopherins and their roles in nuclear transport across eukaryotes.