Molecular evolution of importin

I grabbed this almost at random from a dog-eared 1999 issue of Nature. It serves two purposes:

  • To document a peer-reviewed example of molecular evolution. Michael Behe’s sworn testimony in 2005 stated that this research does not exist. It does— and if you or I don’t understand it fully, that’s due only to our lack of training.
  • To show computer professionals that they might find some kinds of jargon impenetrable, just as some people find theirs difficult to understand—again, due to lack of training.

Title: Structure of importin‑β bound to the IBB domain of importin‑α
Authors: Gino Cingolani, Carlo Petosa, Karsten Weis, Christoph W. Müller
Published: Nature Volume 399, 2 May 1999, page 221


Cytosolic proteins bearing a classical nuclear localization signal enter the nucleus bound to a heterodimer of importin-α and importin-β (also called karyopherin-α and -β). The formation of this heterodimer involves the importin-β-binding (IBB) domain of importin-α, a highly basic amino-terminal region of roughly 40 amino-acid residues. Here we report the crystal structure of human importin-β bound to the IBB domain of importin-α, determined a 2.5 Å and 2.3 Å resolution in two crystal forms. Importin-β consists of 19 tandemly repeated HEAT motifs and wraps intimately around the IBB domain. The association involves two separate regions of importin-β, recognizing structurally distinct parts of the IBB domain: an amino-terminal extended moiety and a carboxyl-terminal helix. The structure indicates that significant conformational changes occur when importin-b binds or releases the IBB domain domain and suggests how dissociation of the importin-α/β heterodimer may be achieved upon nuclear entry.


…[introductory material, 5 paragraphs]

We have solved the crystal structure of human importin-β bound to the IBB domain of human importin-α. The association occurs through a combination of specific-sequence recognition and gross electrostatic complementarity. The structure provides clues as to how the binding of Ran-GTP to importin-β could lead to IBB dissociation, and supports the hypothesis that importins α and β have evolved from a common ancestor.

[Determination of the structure]
[Overview of the complex]
[Structure of importin-β]
[Structure and recognition of the IBB domain]
[Implications for conformational change]
[Comparison of the two crystal forms]
[Interactions with the NPC and with Ran]
[Importins α and β compared]
– Protein expression, purification and crystallization
– Data collection and structure determination]
– table: structure determination of the importin-β-IBB domain complex
– Structure of importin-β bound to the IBB domain of importin-α
— view down the superhelical axis (shown)
— side view
— comparison of importin-β and the protein phosphatases 2A PR65/A subunit
— final 2Fo – Fc electron-density map of the N-terminal IBB moiety in crystal form
– Primary and secondary structures of importin-β and the IBB domain
— IBB domain of human importin-α2 aligned with eight homologues, including human snurportin1
— structural alignments of the 19 HEAT repeats
— a representative HEAT repeat
– Recognition of the IBB domain by importin-β
— electrostatic surface representation of the importin β-IBB domain complex
— a summary of interactions
— interactions involving the N-terminal moiety and the C-terminal helix
— interactions involving the N-terminal moiety and the IBB domain
– Comparison of the complex in two crystal forms
— view along the superhelical axis
— beads-on-a-string representation
– A comparison of importins α and β]


One Response to “Molecular evolution of importin”

  1. JMHO Says:

    Nice Blog:)

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