The Protein S Erlangen Mutation PROS1c.1904T>C (F635S) Suppresses Secretion.

BACKGROUND: The recently identified PROS1 mutation Protein S Erlangen c.1904T>C, resulting in amino acid exchange F635S, is associated with severe quantitative protein S (PS) deficiency and clinical thrombosis. It was hypothesized that this deficiency is due to a secretion defect [1]. This report aims to further elucidate the potential secretion defect of PS Erlangen. METHODS: Coding sequences (CDS) of wild type (WT) PROS1 (encoding PS) and mutated PROS1c.1904T>C (encoding PSF635S) were cloned in front of the CDS of green fluorescent protein (GFP), and the respective plasmids were introduced into HEK293T cells. PROS1-GFP and PROS1c.1904T>C-GFP expressing HEK293T cell lines were analyzed by confocal laser scanning microscopy and western blot for cellular proteins and proteins secreted to the growth medium. RESULTS: Western blot analysis revealed a significantly reduced secretion of PSF635S compared to WT PS. This observation was confirmed by the detection of mutant PSF635S-GFP fusion exclusively in the endoplasmic reticulum (ER), while PS-GFP passed through the entire secretory pathway, as indicated by the localization within both the ER and Golgi apparatus. CONCLUSIONS: The Protein S Erlangen mutation results in type I PS deficiency caused by a secretion defect.

Protein S Erlangen: a novel PROS1 gene mutation associated with quantitative protein S deficiency.

The members of a Caucasian family were genetically analyzed on suspicion of hereditary protein S deficiency. A novel mutation, c.1904T>C, associated with severe quantitative protein S deficiency was found. The novel PROS1 mutation was identified by sequencing of the PROS1 gene coding sequence. The identified c.1904T>C point mutation results in p.Phe635Ser amino acid exchange, which is located in the Laminin G-like 2 domain of protein S. Computational analysis indicates that this amino acid exchange affects the correct folding of the protein S antigen. Furthermore, this mutation is located in a region of the Laminin G-like 2 domain where changes in the amino acid sequence often result in decreased secretion. We postulate that the novel p.Phe635Ser mutation might lead to an incorrect folding, and thus, to a strongly impaired secretion of this protein S variant. We named this novel variant protein.