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Ferrata Storti Foundation
Molecular heterogeneity of pyruvate kinase deficiency
Paola Bianchi and Elisa Fermo
Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico Milano, UOC Ematologia, UOS Fisiopatologia delle Anemie, Milan, Italy
Haematologica 2020 Volume 105(9):2218-2228
ABSTRACT
Red cell pyruvate kinase (PK) deficiency is the most common glycolytic defect associated with congenital non-spherocytic hemolytic anemia. The disease, transmitted as an autosomal recessive trait, is caused by mutations in the PKLR gene and is characterized by molecular and clinical heterogeneity; anemia ranges from mild or fully compensated hemolysis to life-threatening forms necessitating neonatal exchange transfusions and/or subsequent regular transfusion support; complications include gallstones, pulmonary hypertension, extramedullary hematopoiesis and iron overload. Since identification of the first pathogenic variants responsible for PK defi- ciency in 1991, more than 300 different variants have been reported, and the study of molecular mechanisms and the existence of genotype-phenotype correlations have been investigated in-depth. In recent years, during which progress in genetic analysis, next-generation sequencing technologies and personalized medicine have opened up important landscapes for diagnosis and study of molecular mechanisms of congenital hemolytic anemias, geno- typing has become a prerequisite for accessing new treatments and for eval- uating disease state and progression. This review examines the extensive molecular heterogeneity of PK deficiency, focusing on the diagnostic impact of genotypes and new acquisitions on pathogenic non-canonical variants. The recent progress and the weakness in understanding the genotype-phe- notype correlation, and its practical usefulness in light of new therapeutic opportunities for PK deficiency are also discussed.
Pyruvate kinase enzyme
Pyruvate kinase (PK) is an allosterically regulated glycolytic enzyme that cat- alyzes the irreversible conversion of phosphoenolpyruvate to pyruvate, with the synthesis of one molecule of ATP. Since mature red blood cells totally depend on the ATP generated by glycolysis for maintaining cell integrity and function, PK plays a crucial role in erythrocyte metabolism; insufficient energy production may impair red blood cell homeostasis, leading to premature removal of PK-deficient erythrocytes from the circulation by the spleen.1,2 A secondary decrease in PK activ- ity has been observed in the presence of reduced red cell membrane surface (as in hereditary spherocytosis3) or in acquired hematologic conditions (e.g., acute myeloid leukemias, or myelodysplastic syndromes),4,5 suggesting a functional rela- tionship between structural membrane integrity and PK activity, and a wider involvement of glycolytic enzymes in cell control.4,5
The three-dimensional structures of a number of prokaryotic and eukaryotic PK have been solved to a high resolution, showing that in almost all organisms, func- tional PK is a homotetramer of approximately 200-240 kDa.6-9 Each subunit con- tains four domains, namely a small N-terminal helical domain (residues 1-84); an A domain with (β/a)8 barrel topology (residues 85-159 and 263-431); a β-stranded B domain (residues 160-262), inserted between helix a3 and strand β of the A domain, and a C domain with a+β topology (residues 432-574)10,11 (Figure 1A, B). The active site is located between the A and B domains, whereas the C domain contains the binding site for fructose 1,6 bisphosphate.12 Subunit interactions at the interfaces between the A domains and the C domains, as well as A/B and A/C interdomain interactions within one subunit are considered to be key determinants of the allosteric response of the enzyme. PK is quite a stable protein, and can last
Correspondence:
PAOLA BIANCHI,
paola.bianchi@policlinico.mi.it
Received: May 7, 2020. Accepted: July 3, 2020. Pre-published: July 23, 2020.
doi:10.3324/haematol.2019.241141 ©2020 Ferrata Storti Foundation
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