SIL1

The SIL1 gene provides instructions for producing a protein located in a cell structure called the endoplasmic reticulum. Among its many functions, the endoplasmic reticulum folds and modifies newly formed proteins so they have the correct 3-dimensional shape. The SIL1 protein works with BiP, a protein that helps fold newly produced proteins into the proper shape and refold damaged proteins. To start this process, BiP attaches (binds) to a molecule called adenosine triphosphate (ATP). When BiP folds a protein, the ATP is converted to a similar molecule called adenosine diphosphate (ADP). Then SIL1 releases ADP from BiP so that it can bind to another molecule of ATP and start the protein folding process again. Because of its role in helping BiP exchange ADP for ATP, SIL1 is called a nucleotide exchange factor.

Marinesco-Sjögren syndrome - caused by mutations in the SIL1 gene

More than a dozen mutations in the SIL1 gene have been found to cause Marinesco-Sjögren syndrome. Most of these mutations result in the production of a protein that has little or no activity. Defective SIL1 cannot remove ADP from BiP. BiP is then unable to bind to ATP and re-start the protein folding process. A disruption in protein folding impairs protein transport and causes proteins to accumulate in the endoplasmic reticulum. This accumulation likely damages and destroys cells in many different tissues, leading to poor coordination, muscle weakness, and the other features of Marinesco-Sjögren syndrome.