The role of ClpX in erythropoietic protoporphyria

Abstract

Hemoglobin is an essential biological component of human physiology and its production in red blood cells relies upon proper biosynthesis of heme and globin protein. Disruption in the synthesis of these precursors accounts for a number of human blood disorders found in patients. Mutations in genes encoding heme biosynthesis enzymes are associated with a broad class of metabolic disorders called porphyrias. In particular, one subtype – erythropoietic protoporphyria – is caused by the accumulation of protoporphyrin IX. Erythropoietic protoporphyria patients suffer from photosensitivity and a higher risk of liver failure, which is the principle cause of morbidity and mortality. Approximately 90% of these patients carry loss-of-function mutations in the enzyme ferrochelatase (FECH), while 5% of cases are associated with activating mutations in the C-terminus of ALAS2. Recent work has begun to uncover novel mechanisms of heme regulation that may account for the remaining 5% of cases with previously unknown genetic basis. One erythropoietic protoporphyria family has been identified with inherited mutations in the AAA+ protease ClpXP that regulates ALAS activity. In this review article, recent findings on the role of ClpXP as both an activating unfoldase and degrading protease and its impact on heme synthesis will be discussed. This review will also highlight the role of ClpX dysfunction in erythropoietic protoporphyria.

Dimeric ferrochelatase bridges ABCB7 and ABCB10 homodimers in an architecturally defined molecular complex required for heme biosynthesis

“…Alas2, Fech and Alad protein levels decreased in cells lacking Abcb7 (Figure 3B and Online Supplementary Figure S7A ), whereas levels of the heme biosynthetic enzyme Cpox, 25 of Sucla2 and Suclg2, which provide succinyl-CoA to the first rate-limiting step of the pathway. 26 and of the unfoldase Clpx, required for the pyridoxal-phosphate-dependent activation of Alas2, 27 did not change ( Online Supplementary Figure S7A ). Abcb7-KD cells exhibited impaired hemoglobinization (Figure 3C).…”

A mutation in the iron-responsive element of <i>ALAS2</i> is a modifier of disease severity in a patient suffering from <i>CLPX</i> associated erythropoietic protoporphyria

“…Previously we and others described the important role of CLPX in heme biosynthesis through its regulation of ALAS2 turnover and enzyme activity. 11,15 The G298D mutation in the CLPX gene, present in heterozygosity in this family (proband, father and paternal uncle), decreases the proteolytic activity of the CLPXP protease, causing accumulation of ALAS2. 11 However, in comparison to the mild photosensitivity presented by the paternal family, the proband presents with a full and severe EPP phenotype due to the combination of the paternal CLPX G298D mutation and the maternal ALAS2 -38T>C mutation present in the 5' IRE of ALAS2 gene.…”

Controlled movement of ssDNA conjugated peptide through Mycobacterium smegmatis porin A (MspA) nanopore by a helicase motor for peptide sequencing application

“…Compared to well-studied nucleic acid motors, such as polymerases, helicases and translocases, motor proteins that bind to and transport polypeptides have not been extensively characterized. 18,19 To address the poor availability of reliable peptide motor proteins, we hypothesized that nanopore-based peptide transport could be controlled by conjugating the peptide to a single-stranded DNA (ssDNA) handle under the regulation of a DNA helicase. In fact, similar strategies have previously been employed in the investigation of enzyme dynamics, 20 direct microRNA sequencing, and epigenetic analysis.…”