2B7X: Sequential reorganization of beta-sheet topology by insertion of a single strand

Insertions, duplications, and deletions of sequence segments are thought to be major evolutionary mechanisms that increase the structural and functional diversity of proteins. Alternative splicing, for example, is an intracellular editing mechanism that is thought to generate isoforms for 30%-50% of all human genes. Whereas the inserted sequences usually display only minor structural rearrangements at the insertion site, recent observations indicate that they may also cause more dramatic structural displacements of adjacent structures. In the present study we test how artificially inserted sequences change the structure of the beta-sheet region in T4 lysozyme. Copies of two different beta-strands were inserted into two different loops of the beta-sheet, and the structures were determined. Not surprisingly, one insert "loops out" at its insertion site and forms a new small beta-hairpin structure. Unexpectedly, however, the second insertion leads to displacement of adjacent strands and a sequential reorganization of the beta-sheet topology. Even though the insertions were performed at two different sites, looping out occurred at the C-terminal end of the same beta-strand. Reasons as to why a non-native sequence would be recruited to replace that which occurs in the native protein are discussed. Our results illustrate how sequence insertions can facilitate protein evolution through both local and nonlocal changes in structure.
PDB ID: 2B7XDownload
MMDB ID: 158770
PDB Deposition Date: 2005/10/5
Updated in MMDB: 2018/02
Experimental Method:
x-ray diffraction
Resolution: 3  Å
Source Organism:
Similar Structures:
Biological Unit for 2B7X: monomeric; determined by author and by software (PQS)
Molecular Components in 2B7X
Label Count Molecule
Protein (1 molecule)
Lysozyme(Gene symbol: e)
Molecule annotation
Chemicals (2 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB