Homology modeling of human methylmalonyl‐CoA mutase: A structural basis for point mutations causing methylmalonic aciduria

Abstract

Point mutations in the human gene encoding coenzymegive rise to an inherited disorder of propionic acid metabolism termed mut methylmalonic aciduria. Almost all such mutations alter amino acids in the homodimeric human enzyme that are identical to residues in the catalytic a-subunit of the heterodimeric methylmalonyl-CoA mutase from the bacterium Propianibacterium shermanii, to which the mature human enzyme shows an overall 65% sequence identity. To explore how specific mutations might cause the observed clinical phenotype, 12 known mutations were mapped onto a three-dimensional homology model of the subunit of the human enzyme, generated using the program MOD-

N219Y, a new frequent mutation among mut° forms of methylmalonic acidemia in Caucasian patients

“…Most of them affect a residue directly involved in catalysis, but modelling predicts that some mutations act rather by interfering with protein folding. 11 Our modelling analysis of the N219Y mutation suggests that it belongs to this second type. Indeed, substitution of Asn219 by a Tyr residue might severely influence the overall MCM conformation in different ways.…”

“…Mapping of the N219Y substitution on the three-dimensional model of human MCM 11 shows that Asn219 is located in the fourth b-strand of the N-terminal eight-stranded b/a barrel, ie, a specific Figure 2 Partial alignment of methylmalonyl-CoA mutase amino acid sequence around asparagine 219 in various species. Sequences span amino acids 181 ± 255 in Homo sapiens, Mus musculus, Propionibacterium shermanii, Mycobacterium tuberculosis and Escherichia coli enzymes (Swiss Prot accession numbers P22033, P16332, P11653, P71774 and P27253, respectively).…”

“…As notified in Thoma È and Leadlay, 11 the very high amino-acid sequence identity between human MCM and the a subunit of the P. shermanii enzyme allowed the construction of a 3D model that satisfies spatial constraints.…”

Mutation Analysis of Methylmalonyl CoA Mutase Gene Exon 2 in Egyptian Families: Identification of 25 Novel Allelic Variants

“…MCM is encoded by the MUT gene in the nucleus as a 750 amino acid precursor protein and transported then into the mitochondrial matrix, where its 32 amino acid mitochondrial leader sequence is cleaved (Jansen and Ledley, 1990). The mature enzyme, 718 amino acids in size, forms a homodimer of α and β subunits, each subunit binds 1 molecule of adenosylcobalamin (Thomä and Leadlay, 1996). MCM mitochondrial leader sequence (residues 1-32) is followed by the N-terminal extended segment (residues 33-87), which is involved in subunit interaction.…”

“…MCM mitochondrial leader sequence (residues 1-32) is followed by the N-terminal extended segment (residues 33-87), which is involved in subunit interaction. The N-terminal (βα) 8 barrel is the substrate binding domain (residues 88-422) and is attached to the C-terminal (βα) 5 domain (cobalamin binding domain, residues 578-750) by a long linker region (residues 423-577) (Thomä and Leadlay, 1996).…”