title: Chaperone therapy for homocystinuria: the rescue of CBS mutations by heme arginate.
abstract: Classical homocystinuria is caused by mutations in the cystathionine β-synthase (CBS) gene. Previous experiments in bacterial and yeast cells showed that many mutant CBS enzymes misfold and that chemical chaperones enable proper folding of a number of mutations. In the present study, we tested the extent of misfolding of 27 CBS mutations previously tested in E. coli under the more folding-permissive conditions of mammalian CHO-K1 cells and the ability of chaperones to rescue the conformation of these mutations. Expression of mutations in mammalian cells increased the median activity 16-fold and the amount of tetramers 3.2-fold compared with expression in bacteria. Subsequently, we tested the responses of seven selected mutations to three compounds with chaperone-like activity. Aminooxyacetic acid and 4-phenylbutyric acid exhibited only a weak effect. In contrast, heme arginate substantially increased the formation of mutant CBS protein tetramers (up to sixfold) and rescued catalytic activity (up to ninefold) of five out of seven mutations (p.A114V, p.K102N, p.R125Q, p.R266K, and p.R369C). The greatest effect of heme arginate was observed for the mutation p.R125Q, which is non-responsive to in vivo treatment with vitamin B(6). Moreover, the heme responsiveness of the p.R125Q mutation was confirmed in fibroblasts derived from a patient homozygous for this genetic variant. Based on these data, we propose that a distinct group of heme-responsive CBS mutations may exist and that the heme pocket of CBS may become an important target for designing novel therapies for homocystinuria.
authors.affiliation: Institute of Inherited Metabolic Disorders, Charles University in Prague-First Faculty of Medicine and General University Hospital in Prague, Ke Karlovu 2, 128 08, Praha 2, Czech Republic.
authors.forename: Petra
authors.initials: P
authors.lastname: Melenovská
authors.forename: Jana
authors.initials: J
authors.lastname: Kopecká
authors.forename: Jakub
authors.initials: J
authors.lastname: Krijt
authors.forename: Aleš
authors.initials: A
authors.lastname: Hnízda
authors.forename: Kateřina
authors.initials: K
authors.lastname: Raková
authors.forename: Miroslav
authors.initials: M
authors.lastname: Janošík
authors.forename: Bridget
authors.initials: B
authors.lastname: Wilcken
authors.forename: Viktor
authors.initials: V
authors.lastname: Kožich
mesh_terms: D000818:Animals; D001120:Arginine / Q000494:pharmacology*; D016466:CHO Cells; D020134:Catalytic Domain; D003412:Cricetulus; D003541:Cystathionine beta-Synthase / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000187:drug effects* / Q000201:enzymology; D020022:Genetic Predisposition to Disease; D006418:Heme / Q000494:pharmacology*; D006712:Homocystinuria / Q000175:diagnosis / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics; D006720:Homozygote; D006801:Humans; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000494:pharmacology*; D009154:Mutation; D010641:Phenotype; D011487:Protein Conformation; D017510:Protein Folding; D057165:Proteostasis Deficiencies / Q000175:diagnosis / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014162:Transfection
chemical_list: D018832:Molecular Chaperones; D006418:Heme; D001120:Arginine; D003541:Cystathionine beta-Synthase; C048849:heme arginate