FUNCTIONAL EXPRESSION OF HUMAN MUTANT PHOSPHOFRUCTOKINASE IN YEAST - GENETIC-DEFECTS IN FRENCH-CANADIAN AND SWISS PATIENTS WITH PHOSPHOFRUCTOKINASE DEFICIENCY

Human phosphofructokinase (PFK) is a tetrameric enzyme, encoded by mus cle, liver, and platelet genes. Deficiency of muscle PFK (PFK-M), glyc ogenosis type VII (Tarui disease), is an autosomal recessive disorder characterized by an exertional myopathy and hemolytic syndrome. Severa l disease-causing mutations have been identified in the PFK-M gene in Japanese, Ashkenazi Jewish, and Italian patients. We describe the gene tic defects in French Canadian and Swiss patients with the disease, an d we use a genetically well-defined yeast system devoid of endogenous PFK for structure-function studies of the mutant PFKs. A G-to-A transi tion at codon 209-in exon 8 of the PFK-M gene, changing an encoded Gly to Asp, is responsible for the disease in a homozygous French Canadia n patient. Gly-209-mutated protein is completely inactive in the yeast system. The Swiss patient is a genetic compound, carrying a G-to-A tr ansition at codon 100 in exon 6 (Arg to Gin) and a G-to-A transition a t codon 696 in exon 22 (Arg to His). The mutants expressed in yeast ge nerate functional enzyme with modest changes in thermal stability. The advantages and limitations of the yeast system for expression of huma n mutant PFKs are discussed.