In silico and in vivo models for Qatari-specific classical homocystinuria as basis for development of novel therapies.

Valeria Di Giacomo, Senior R&D Researcher in ZeClinics, presents a new paper in collaboration with Qatar University.

Hesham M Ismail ^1 2, Navaneethakrishnan Krishnamoorthy ^3 4, Nader Al-Dewik ⁵, Hatem Zayed ¹, Nura A Mohamed ², Valeria Di Giacomo ⁶, Sapna Gupta ⁷, Johannes Häberle ⁸, Beat Thöny ⁸, Henk J Blom ⁹, Waren D Kruger ⁷, Tawfeg Ben-Omran ⁵, Gheyath K Nasrallah ^1 2

¹Department of Biomedical Sciences, College of Health Sciences, Qatar University, Doha, Qatar.

²Biomedical Research Center, Qatar University, Doha, Qatar.

³Systems Biology Department, Sidra Medical and Research Centre, Doha, Qatar.

⁴Heart Science Centre, National Heart and Lung Institute, Imperial College London, London, UK.

⁵Clinical and Metabolic Genetics, Department of Pediatrics, Hamad Medical Corporation, Doha, Qatar.

⁶ZeClinics SL, PRBB (Barcelona Biomedical Research Park), Barcelona, Spain.

⁷Cancer Biology Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania.

⁸University Children's Hospital and Children's Research Center, Division of Metabolism, Zurich, Switzerland.

⁹Laboratory of Clinical Biochemistry and Metabolism, Department of General Pediatrics, Adolescent Medicine and Neonatology, University Medical Centre Freiburg, Freiburg, Germany.

ABSTRACT

Homocystinuria is a rare inborn error of methionine metabolism caused by cystathionine β-synthase (CBS) deficiency. The prevalence of homocystinuria in Qatar is 1:1,800 births, mainly due to a founder Qatari missense mutation, c.1006C>T; p.R336C (p.Arg336Cys). We characterized the structure-function relationship of the p.R336C-mutant protein and investigated the effect of different chemical chaperones to restore p.R336C-CBS activity using three models: in silico, ΔCBS yeast, and CRISPR/Cas9 p.R336C knock-in HEK293T and HepG2 cell lines. Protein modeling suggested that the p.R336C induces severe conformational and structural changes, perhaps influencing CBS activity. Wild-type CBS, but not the p.R336C mutant, was able to restore the yeast growth in ΔCBS-deficient yeast in a complementation assay. The p.R336C knock-in HEK293T and HepG2 cells decreased the level of CBS expression and reduced its structural stability; however, treatment of the p.R336C knock-in HEK293T cells with betaine, a chemical chaperone, restored the stability and tetrameric conformation of CBS, but not its activity. Collectively, these results indicate that the p.R336C mutation has a deleterious effect on CBS structure, stability, and activity, and using the chemical chaperones approach for treatment could be ineffective in restoring p.R336C CBS activity.

View full article HUMAN MUTATION