Residual activity and proteasomal degradation of p.Ser298Pro sulfamidase identified in patients with a mild clinical phenotype of Sanfilippo A syndrome

Abstract

Mucopolysaccharidosis type IIIA (MPS IIIA, Sanfilippo syndrome) is a fatal inherited lysosomal storage disease accompanied by progressive neurologic degeneration. The gene underlying MPS IIIA, SGSH, encodes a lysosomal enzyme, N-sulfoglucosamine sulfohydrolase (sulfamidase). Mutational analysis of a large cohort of MPS IIIA patients showed a correlation of the missense mutation p.Ser298Pro and a slowly progressive course of the disease. We report here on the expression of the mutant p.Ser298Pro sulfamidase in BHK cells retaining low residual activity. Pulse-chase experiments showed that rapid degradation is responsible for the low steady state level of the mutant protein. Processing and secretion of p.Ser298Pro sulfamidase suggests that small amounts of the newly synthesized enzyme are transported to lysosomes. Most of the mutant sulfamidase exits the endoplasmic reticulum for proteasomal degradation. The ability to predict the clinical course of MPS IIIA in patients with the p.Ser298Pro mutation, as well as the residual enzymatic activity, and the reduced stability of the mutant sulfamidase suggest that this subgroup of patients is especially well suited to early sulfamidase replacement therapy or treatment with selective pharmacological chaperones.

Proteasome Composition and Activity Changes in Cultured Fibroblasts Derived From Mucopolysaccharidoses Patients and Their Modulation by Genistein

“…These results are compatible with previous reports (describing results of studies on single MPS types) which indicated enhanced expression of genes coding for proteasomal proteins in MPS I (Khalid et al, 2016), rapid proteasomal degradation of mutant forms of iduronate-2-sulfatase in MPS II (Osaki et al, 2018;Marazza et al, 2020), rapid proteasomal degradation of mutant N-sulfoglucosamine sulfhydrolase (Muschol et al, 2011) and cysteine string protein α (CSPα) (Sambri et al, 2017), as well as elevated levels of the 19S proteasomal subunit (Beard et al, 2017) in MPS IIIA, and rapid proteasomal degradation of synaptophysin in MPS IIIB (Vitry et al, 2009). Nevertheless, results presented in this report provided global picture of proteasomal changes in all MPS types.…”

Recommendations on clinical trial design for treatment of Mucopolysaccharidosis Type III

“…However, there is a great degree of variability both within and between subtypes [25, 27]. Very attenuated phenotypes have been reported, usually in association with specific mutations [30–34]. Specific mutations associated with severe or attenuated phenotypes are well recognised in MPS IIIA [30] but not MPS IIIB.…”

Structure of sulfamidase provides insight into the molecular pathology of mucopolysaccharidosis IIIA

“…Phenotype Blanch et al (1997), Weber et al (1997), Di Natale et al (1998), Montfort et al (1998) Di Natale et al (1998Natale et al ( , 2003 V131M et al (1997), Bunge et al (1997), Weber et al (1997Weber et al ( , 1998, Beesley et al (2000), Muschol et al (2004Muschol et al ( , 2011, Meyer et al (2008) but also lie in close proximity to the C-terminus, including Leu487, Glu488, Pro497, Leu498 and the third-last residue Asn500. Nonsense mutations where even a relatively minor part of domain 2 is missing may be predicted to be destabilizing to the dimer interface.…”