One gene, many proteins

Structural consequences of genetic editing.

Structural analysis of a molecule key to the interaction between muscle and nerve cells has led Swiss researchers to a novel insight on the genetic cut-and-paste process of alternative splicing, whereby one gene encodes several different gene products.

J?rg Stetefeld at the University of Basel, Switzerland, and colleagues are interested in the modular proteoglycan agrin, which exists in several isoforms. The name agrin comes from the Greek ’to connect’, and the molecule is an essential component of the neuromuscular junction.

The researchers analysed four so-called splice variants of the protein’s globular C-terminal domain, G3. Splicing refers to the rearrangements (insertions or deletions) that occur when a DNA sequence is transcribed into the messenger RNA template, which then encodes the final protein.

The four protein variants analysed contain insertions of 8, 11, 19 (a combination of 8 and 11) or 0 amino acids. The structures of the first two of these (called B8 and B11) were determined by X-ray crystallography, and the structure without inserts (B0) was determined by nuclear magnetic resonance. The team is still working on B19.

As far as the researchers are aware, this is the first study to have resolved the structures of several splice variants of one gene.

Resolving these structure will help determine the protein’s functions (which are essential, since mice without the gene die at birth), and could lead researchers to the elusive agrin receptor, which has remained a mystery for years. Finding it would be worthy of a Nobel prize, says Stetefeld.

Co-author Andrei Alexandrescu of the University of Connecticut, US, thinks they’re a step closer. ’An obvious direction for the future is to structurally characterise the interactions between agrin and some of its binding partners, such as the putative agrin receptor.’

Bea Perks