Structure
The MT-ND4L gene is located in human mitochondrial DNA from base pair 10,469 to 10,765. The MT-ND4L gene produces an 11 kDa protein composed of 98 amino acids. MT-ND4L is one of seven mitochondrial genes encoding subunits of the enzyme NADH dehydrogenase (ubiquinone), together with MT-ND1, MT-ND2, MT-ND3, MT-ND4, MT-ND5, and MT-ND6. Also known as Complex I, this enzyme is the largest of the respiratory complexes. The structure is L-shaped with a long, hydrophobic transmembrane domain and a hydrophilic domain for the peripheral arm that includes all the known redox centres and the NADH binding site. MT-ND4L and the rest of the mitochondrially encoded subunits are the most hydrophobic of the subunits of Complex I and form the core of the transmembrane region.
An unusual feature of the human MT-ND4L gene is the 7-nucleotide gene overlap of its last three codons (5'-CAA TGC TAA-3' coding for Gln, Cys and Stop) with the first three codons of the MT-ND4 gene (5'-ATG CTA AAA-3' coding for amino acids Met-Leu-Lys). With respect to the MT-ND4L reading frame (+1), the MT-ND4 gene starts in the +3 reading frame: [CAA][TGC][TAA]AA versus CA[ATG][CTA][AAA].
Clinical significance
Mitochondrial dysfunction resulting from variants of MT-ND4L, MT-ND1 and MT-ND2 have been linked to BMI in adults and implicated in metabolic disorders including obesity, diabetes and hypertension.
A T>C mutation at position 10,663 in the mitochondrial gene MT-ND4L is known to cause Leber's Hereditary Optic Neuropathy (LHON). This mutation results in the replacement of the amino acid valine with alanine at position 65 of the protein ND4L, disrupting function of Complex I in the electron transport chain. It is unknown how this mutation leads to the loss of vision in LHON patients, but it may interrupt ATP production due to the impaired activity of Complex I. Mutations in other genes encoding subunits of Complex I, including MT-ND1, MT-ND2, MT-ND4, MT-ND5, and MT-ND6 are also known to cause LHON.
