STRUCTURAL STUDIES OF CALRETICULIN AND SACSIN

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The calnexin cycle is a cellular process when secretory proteins are translocated into the lumen of the endoplasmic reticulum (ER) to become N-glycosylated and folded. The control components of the process are the membrane protein calnexin (CNX) and its soluble homologue calreticulin (CRT) that selectively recognize glycoproteins. CRT consists of a globular lectin-like domain, a hairpin-like proline-rich domain and an unstructured C-terminus rich in acidic residues. Recent studies suggest that CRT also functions as a chaperone by directly binding hydrophobic polypeptides via binding site in the globular domain. Here, we crystallized the globular domain of calreticulin. The structure will help to identify residues involved in glycoprotein binding and chaperoning activities. Autosomal recessive spastic ataxia of Charlevoix¿¿"Saguenay (SACS) is an early-onset neurodegenerative disease with high prevalence in the Charlevoix¿¿"Saguenay¿¿"Lac-Saint-Jean region of Quebec (Canada). The gene responsible for ARSACS produces a single protein SACSIN (4579 aa, MW=520 kDa). The function of the protein is unknown. The N-terminal part of the protein contains a domain with weak sequence similarity to ubiquitin-like (UBL) domains. The structure will provide insights into functional role of SACSIN.