The Molecular Basis Underlying Heme Biosynthesis Dysfunction and Disease Originating from C-Terminal Mutations in Aminolevulinic Acid Synthase
Taylor, Jessica
0000-0003-4083-7545
:
2024-07-05
Abstract
Aminolevulinic acid synthase (ALAS) is a conserved heme biosynthetic enzyme that catalyzes the first, rate-limiting step of heme biosynthesis in non-plant eukaryotes and alphaproteobacteria. Vertebrates evolved to have two isoforms of ALAS that include the ubiquitously expressed isoform, ALAS1, and the erythroid-specific isoform, ALAS2. ALAS2 takes on the heavy heme requirement that accompanies erythropoiesis. Because of the critical role that ALAS2 plays in developing red blood cells, mutations in ALAS2 lead to functional implications in the heme biosynthesis pathway and result in blood disease. Mutations in ALAS2 lead to a gain-of-function disease, X-linked protoporphyria (XLP), or a loss-of-function disease, X-linked sideroblastic anemia (XLSA). Interestingly, mutations in the ALAS2 C-terminal extension can be implicated in both diseases. The molecular basis for ALAS2 dysfunction mediated by two C-terminal loss-of-function variants, hALAS2 V562A and M567I, was investigated. Two distinct mechanisms of loss-of-function were found to underlie the pathogenesis of XLSA from V562A and M567I. V562A results in decreased enzyme stability and reduced enzyme efficiency concerning succinyl-CoA substrate binding. M567I was found to significantly alter the cooperativity of both glycine and succinyl-CoA substrate binding which coincided with decreased enzyme activity. Together, these data provide the first molecular explanation for loss-of-function underlying XLSA in V562A and M567I. ALAS2 protein interactors were also explored, and it was established that further investigations are needed to dissect the interaction between ALAS2 and its putative binding partner succinyl-CoA synthetase.