Structural and functional analysis of mutations in alkaptonuria

Abstract

Alkaptonuria (AKU), the prototypic inborn error of metabolism, was the first human disease to be interpreted as a Mendelian trait by Garrod and Bateson at the beginning of last century. AKU results from impaired function of homogentisate dioxygenase (HGO), an enzyme required for the catabolism of phenylalanine and tyrosine. With the novel 7 AKU and 22 fungal mutations reported here, a total of 84 mutations impairing this enzyme have been found in the HGO gene from humans and model organisms. Forty-three of these mutations result in single amino acid substitutions. This mutational information is analysed here in the context of the HGO structure and function using kinetic assays performed using purified AKU mutant enzymes and the crystal structure of human HGO. HGO is a topologically complex structure which assembles as a functional hexamer arranged as a dimer of trimers. We show how the intricate pattern of intra- and inter-subunit interactions and the extensive surfaces required for subunit folding and association of this oligomeric enzyme can be inactivated at multiple levels by single-residue substitutions. This explains, in part, the predominance of missense mutations (67%) in AKU.

Twelve novel HGD gene variants identified in 99 alkaptonuria patients: focus on ‘black bone disease’ in Italy

“…36 So far, observed absence of a clear correlation between genotype and phenotype may be explained by the variability in residual HGD enzymatic activities caused by different mutations. 19 Owing to the complex hexameric structure of the HGD enzyme, genotype-phenotype correlation studies are even more complicated when in the patients two different mutations are to be considered.…”

Alkaptonuric Ochronosis with Aortic Valve and Joint Replacements and Femoral Fracture: A Case Report and Literature Review

“…17,18 A total of 84 mutations impairing this enzyme have been found in the HGO gene from humans and model organisms, and 43 of these mutations result in single amino acid substitutions. 19 More than 40 different mutations have been identified in approximately 100 unrelated patients with alkaptonuria from many different countries. 20 The most widespread HGO mutations are probably old mutations that have spread throughout Europe and Asia during human migration.…”

A Fungal Perspective on Human Inborn Errors of Metabolism: Alkaptonuria and Beyond

“…Forty causative mutations (representing a remarkably high allelic heterogeneity for a rare disease) have been identified in patients, mostly thanks to the efforts of S. Rodriguez de Có rdoba and colleagues (see a complete reference list in Rodriguez et al (2000)). Of these, 67% represent missense mutations.…”